Fire Protection

The following technical information is from FireFly and PROdetec:

How to Protect Industrial Processes from Fire and Dust Explosions - Anything that has been transformed into fine particles can explode. Unfortunately, all too often it does. Every year, many serious fires and explosions occur in industrial plants as a result of dust. Yes, dust. Fine inflammable material is explosive! The statistics speak for themselves. Dust explosions lead to considerable material damage and long production shutdowns. Every year there are also accidents with fatal consequences.

Extinguishing is as Important as Detection - This technical bulletin covers;

• Water Extinguishing - Different applications and problems of fire require totally different types of water extinguishing methods. Large water droplets with powerful full cone water spray is needed to penetrate material flows in chutes or pneumatic conveying systems. For extinguishing of flames in enclosed volumes or open areas, smaller droplet sizes are an advantage due to their high evaporation rate, efficient heat absorption and its ability to displace oxygen. Designing a superior extinguishing system is a well-defined science.
• Isolation and Inerting - In some processes, gas may be more suitable as an extinguishing agent. Carbon dioxide and nitrogen are excellent extinguishing agents provided that the affected section of the process can be isolated. This requires extremely fast acting valves.
• Diverting - Another extinguishing method used in the Firefly system is mechanical diverting. When an ignition source has been detected, a divert valve is opened which redirects the material flow out of the process line. The process itself need not even be stopped.
• Steam Extinquishing - The choice of extinguishing agent is generally determined by the products handled in the process. Another factor is the availability of an extinguishing agent.

Other Links

Fire Protection adds Value to Offshore Project Planning - Larry Watrous - The importance of fire protection in the design and construction of offshore structures can be a critical factor in the success of today’s offshore oil and gas projects. Integrating this component into the planning of a production facility is taking on increasing importance. This article addresses the changing needs and expectations, scope of equipment and services, and regulation in the fire protection discipline, as well as the capabilities and roles of the fire protection professional. The article further emphasizes the timing necessary for implementing a formal fire protection program in the design and construction of new offshore structures or the revamping of existing facilities, and the need for the expertise of a trained fire protection engineer to be involved with the development of all phases of these projects - from Mustang Engineering.

Design Engineering Key to Adequate Fire Protection - Larry Watrous - This article has useful tips on the skills required of a Fire Protection Engineer - from Mustang Engineering.

Fire and Explosion Guidance Part 2: Avoidance and Mitigation of Fires - The primary objective of this document is to offer guidance on practices and methodologies which can lead to a reduction in risk to life, the environment and the integrity of offshore facilities exposed to fire hazards - from Logical Software.

Fire Systems Integrity Assurance - Experience has shown that fire detection and protection systems are not always designed or specified in sufficient detail to ensure that they meet the performance criteria necessary to reliably achieve their intended role; this can result in fire systems not providing the performance required when called upon to do so. The OGP has produced a Fire System Integrity Assurance report, which provides guidance on issues involved in the assurance of fire system integrity from development of appropriate performance criteria through to routine system testing and inspection, in order to assess ongoing performance against the original criteria. The objective of the report is to provide a high level model of the steps to be addressed in assuring fire system integrity and to give guidance on technical points to be considered at each stage, drawing on practical experience from oil and gas installations - from OGP.

Fire Prevention Requirements for Information and Communication Technology (ICT) rooms - Best Practice Document - This document provides specification of the Norwegian HE sector’s recommended fire protection requirements for ICT rooms. The aim of this document is to raise personnel awareness concerning the fire protection issue, and to enhance the quality of fire protection measures within the sector. Furthermore, it is intended that the recommendations in this document will form the basis of expansion, renovation and new building projects, and that they will be applied in everyday work contexts - from Terena.

The Fire Industry Association (FIA) is a not-for-profit trade association with the aim of promoting the professional status of the UK fire safety industry. The FIA's main objective is to promote the professional standards of the fire industry. They provide technical knowledge and advice to anyone who needs it regarding fire safety in the UK. This site is an excellent Fire Detection and Protection resource. It provides:

• Technical Updates - General technical information of interest. This includes consultation requests from UK Government on new or proposed legislation, public comment drafts of Standards, and comment drafts of FIA technical documents as well as the notification of publication of new standards and legislation.
• Fact Files - Fact Files are a collation of technical, legislative or procedural facts on a single subject or closely associated group.
• Guidance Notes - These are recommendations and interpretations by the FIA (written by Council, Committee, and Secretariat etc) to give help and guidance to members and non-members on technical subjects, legislative matters, FIA processes/procedures etc.
• Codes of Practice - These are ‘how to’ documents that are drafted and formatted in a similar fashion to a national standard by the FIA (written by Council, Committee, and Secretariat etc) to give help and guidance to members and non-members, primarily on technical subjects.

Protection of Piping Systems Subject To Fires and Explosions - This document aims to fill this gap by providing guidance on the protection and response of piping systems and piping supports subject to fires and explosions. The guidance covers the methods used to carry out both simplified design checks and advanced non linear analysis - from HSE (UK).

Please Scroll Down to see the Various Fire Protection Methods

Enclosure Fire Protection

Enclosure Passive Fire Protection

Innovative Passive Fire Protection Cabinets Extend Margin of Safety for Critical Plant Shutdown Equipment - The cabinets ensure that equipment such as emergency shutdown valves remain operational by keeping them below 60 degrees Centigrade for periods of up to 64 minutes in the event of a hydrocarbon-based fire, to allow time for controlled shutdown - from Intertek.

Enclosures Protected by Gaseous Fire Fighting Systems

Guidance on the Pressure Relief and Post Discharge Venting of Enclosures Protected by Gaseous Fire Fighting Systems - This document provides guidance on fulfilling the requirements contained in BS EN15004-1 and BS 5306-4, in respect to over and under pressurisation venting - clauses 7.4.1 and 10.3.3. respectively and post discharge extract - clauses 5.3 h) and 15.9 respectively. It considers the design, selection and installation of vents to safeguard the structural integrity of enclosures protected by fixed gaseous fire fighting systems and the post discharge venting provisions where used - from the FIA.

Carbon Dioxide

Carbon Dioxide is a tried and trusted fire Protection concept, which basically dumps C02 into an area limiting any oxygen and suffocating any fire. The major disadvantage with this is the risk to human life, hence considerable effort has to be ensured in ensuring human evacuation before the dump occurs.

Why are HALONS no longer used as Fire suppression systems?

Halon fire-fighting systems were banned on new buildings from July 1992 because of the detrimental effects of CFC-based products on the ozone layer.

 

Hi-Fog Systems

The principle of operation of the Hi-fog system is that the spray heads are all activated simultaneously to propel the small water droplets which have a greater surface area at very high momentum into the whole space which act to absorb the fire’s energy. The droplets vaporise almost completely, cooling the flames and forming steam that displaces the oxygen. The result is rapid and efficient and the extinguishing effect is combined with the cooling of the surrounding air, flue gases and surfaces to prevent re-ignition. Hi-fog’s sprinklers have a suction effect that draws in the gases, cools them and washes particles to the floor. The suction in the small sprinkler is 10m³/min and can be up to 25m³/min in the large.

Advantages of the Hi-fog system are:

• Uses small amounts of fresh water, with no additives, stored in high – integrity cylinders.
• It is highly effective against all types of hydrocarbon fires.
• The small quantity of water used means that water damage is negligible.
• It does not damage the environment.
• Superior fire suppression.
• Reduced smoke damage.
• Lightweight.
• Small pipe sizes.
• Fast and easy installation.
• Fast extinguishing.
• Effective cooling and cleaning of smoke.
• Electric power not required.

Disadvantages of the Hi-fog system are:

• It has not been proven in enclosures of more than 1000 cubic metres volume.
• The article "Low and High Pressure Water Mist for critical areas" gives a good overview.

Code of Practice for the Design and Installation of Commercial and Industrial Watermist Systems - This Code of Practice gives recommendations for the design, installation, commissioning and maintenance of watermist systems, and gives performance criteria for fixed watermist systems for specific commercial and industrial hazards. Annex A of this Code provides a template for the testing and validation of watermist system applications by qualified fire testing laboratories. The Code of Practice does not cover watermist systems on ships, in aircraft, on vehicles and mobile fire appliances or for below ground systems in the mining industry. It does not cover the use of watermist for explosion protection.

Using High Pressure Water Mist Fire Protection Systems for Offshore Oil Drilling and Producing Facilities - Larry W Owen - Almost every portion of the platform requires some form of fire protection. Many of the spaces found on offshore oil drilling and production facilities can be protected with water mist systems. Water mist systems have tremendous fire suppression and extinguishing capabilities whether the area protected contains flammable liquids or ordinary combustibles. System testing protocols developed by the International Maritime Organization (IMO) have set the standard for water mist design requirements. Coupled with the National Fire Protection Association (NFPA) 750 Standard on Water Mist Fire Protection, these global guidelines set the benchmark for fire protection engineering companies to use when designing water mist systems. Water mist systems provide suppression and extinguishment of fires through the use of three primary mechanisms, cooling, oxygen depletion (inerting) and radiant heat blocking - from touch briefings.

Water Mist for Fire Protection of Heritage - This is an excellent technical paper which provides a vast amount of information on water mist systems. Water mist application is the most subtle way of water extinguishing. It provides safe and practical environment for rescue work, it protects visitors and staff, it incur minimal secondary damage in valid or unintentional activations and substantially remove harmful particles from smoke. Apart from the above and general extinguishing capabilities of water, mist applications add several advantages over standard sprinkler systems, which often justifies a moderate extra cost. Mist systems discharge less water and use small-diameter pipes. Water supply may not run empty, as does limited gas supplies or other extinguishing media. Water mist may be turned off and on again. Water mist can be used where water was not previously considered practical. Water mist is used in hand held extinguishers, fire hose nozzles, small standalone units, object protection systems, room filling systems, hand held impact guns and large water mist impact monitors. Applications include museum vaults, heritage buildings, hotels, churches and art galleries - from heritagefire.net.

 

Inergen Fire Suppressent Systems

The name INERGEN is derived from a combination of INERTgas and nitrogen.

The composition of the gas "Inergen" (IG-541 or 52.40.08) is Nitrogen (52+/-4%), Argon (40+/-4%) and Carbon Dioxide (8+/1%) of which the concentration used is 35-50%.

The atmosphere consists of 21% Oxygen, 78% Nitrogen, 0.02% Carbon Dioxide and a variety of other gases.

When INERGEN is introduced into the atmosphere the resulting compositions are as follows:

• 66.5 to 70% Nitrogen
• 11.5 to 16.4% Oxygen
• 3.1 to 4.3% Carbon Dioxide

This resulting composition can extinguish fires caused by a wide range of flammable liquids, gases and solids. It achieves its effect by reducing the oxygen level.

The volume calculations of the protected areas are critical and hence it is recommended that they be double-checked to ensure accuracy.

INERGEN SYSTEMS are environmentally friendly and are very safe when sized correctly. People are still able to breathe in the reduced levels of Oxygen and exit the area without risk to their health. The reduced Oxygen level does not support combustion.

The disadvantages of INERGEN include that it should only be used for total flooding applications and that the enclosure around the fire hazard should be tight enough to hold the required concentration of Inergen for a period sufficient to extinguish a fire. In addition if a Halon system is being replaced the volume required is larger, hence the bottle storage area may become a problem.

FM200 - Fire Suppressent Agent

FM-200 is chemically known as heptafluropropane and is sometimes referred to as HFC-227ea. It is a colourless, liquefied compressed gas. It is stored as a liquid and dispensed into the hazard as an electrically non-conductive vapour. FM200 extinguishes fire by both its chemical effect (80%) and its physical effect (20%). It has been classified as being suitable for use as a total flooding agent in occupied areas.

FM200 is effective as a fire extinguishing agent for use on Class A surface fires, Class B flammable liquid fires and Class E electrical fires.

Although FM200 is considered non-toxic to humans in concentrations used for fighting fires certain safety considerations should be considered when handling and applying the agent.

The major disadvantage of FM200 is that it decomposes to form halogen acids when exposed to open flames. The discharge from FM200 may create a hazard to personnel from the natural agent itself and from these products of decomposition that result when the agent is exposed to fire or other hot surfaces. Exposure to the agent is generally of less concern than the exposure to decomposition products, however both should be avoided. The formation of these acids is minimised by using early warning detection systems and proper system installation.

Pyrogen

Pyrogen is described as being the world's first commercially available Aerosol Fire Extinquishing System get more information from: http://www.pyrogen.co.uk/downloads/PyroGen%20(2008)%20brochure.pdf

Very Early Smoke Detection

Very early smoke detection systems are used for the sensitive electronic detection of smoke. They are used as an early warning system.

A typical very early smoke detection system consists of five major components:

1. The air sample transport system (usually small diameter PVC pipes).
2. A filtering arrangement to remove large dust particles.
3. An optical detector that carries out the actual examination of the air sample.
4. An air pump that keeps the air samples moving through the system.
5. The controller electronics that interprets the detector's results.

The sampling pipe or pipes are connected directly to a dust filter designed to remove particles greater than 25 microns in diameter. Dust particles greater than this size have been proved to be potentially troublesome and eliminated by filtering. When the air sample enters the detector chamber, it is exposed to an intense light flash from a Xenon lamp. An extremely sensitive photoelectronic receiver detects light scattered off particles suspended in the air stream. The resulting signal is amplified and processed to produce an analog reading of the smoke intensity. The steam of air is continuously refreshed.

Systems that use broad-spectrum light sources such as Xenon are much more sensitive in a much broader spectral bandwidth than those that rely on light emitting diodes. Xenon closely emulates the spectrum, the intensity of sunlight and it covers the complete spectrum. It extends well into the ultraviolet and deeply into the infrared. Therefore the detector can respond to particles of all sizes and it performs well for a wide range of possible fuels and throughout the stages of fire growth.

Gas Detection

There is a Massive amount of Technical Engineering Information for Instrument and Fire & Gas Engineers on this page - so make life easy and Go the Subject Area that you are interested in:- Principles of Gas Detection | Gas Detection Technical References | Comparison of Gas Detection Technologies | Maintenance of Gas Detection Systems | Planning and Designing Gas Detection Systems | Addressable Gas Detectors | Air Duct Gas Detection | Catalytic Combustible Gas Detectors | Calibrating Gas Sensors | Calibration Gas for Gas Detectors | Open Path Infra Red Gas Detectors | Gas Detection Certification | Gas Detection using Laser Technology | Gas Detection using Photoacoustic Infrared Technology | Gas Detection in Gas Turbines and Compressor Stations | Gas Detection Standards | Portable Gas Detection | Portable Gas Detection Bump Testing | Photoionization Detectors | Toxic Gas Monitors | Ultrasonic Gas Leak Detection

 

Principles of Gas Detection

The following excellent text is provided by Honeywell Analytics - ICEweb is a Free Technical Information Website for Instrument, Control, Fire & Gas and SIS Engineers. 

Combustible Gas Sensors

Many people have probably seen a flame safety lamp at some time and know something about its use as an early form of ‘firedamp’ gas detector in underground coal mines and sewers.

Although originally intended as a source of light, the device could also be used to estimate the level of combustible gases - to an accuracy of about 25-50%, depending on the user’s experience, training, age, colour perception etc. Modern combustible gas detectors have to be much more accurate, reliable and repeatable than this and although various attempts were made to overcome the safety lamp’s subjectiveness of measurement (by using a flame temperature sensor for instance), it has now been almost entirely superseded by more modern, electronic devices.

Nevertheless, today’s most commonly used device, the catalytic detector, is in some respects a modern development of the early flame safety lamp, since it also relies for its operation on the combustion of a gas and its conversion to Carbon Dioxide and water.

Catalytic Sensor

Nearly all modern, low-cost, combustible gas detection sensors are of the electro-catalytic type. They consist of a very small sensing element sometimes called a ‘bead’, a ‘Pellistor’, or a ‘Siegistor’ - the last two being registered trade names for commercial devices. They are made of an electrically heated platinum wire coil, covered first with a ceramic base such as Alumina and then with a final outer coating of Palladium or Rhodium catalyst dispersed in a substrate of Thoria.

This type of sensor operates on the principle that when a combustible gas/air mixture passes over the hot catalyst surface, combustion occurs and the heat evolved increases the temperature of the ‘bead’. This in turn alters the resistance of the platinum coil and can be measured by using the coil as a temperature thermometer in a standard electrical bridge circuit. The resistance change is then directly related to the gas concentration in the surrounding atmosphere and can be displayed on a meter or some similar indicating device.

Sensor Output

To ensure temperature stability under varying ambient conditions, the best catalytic sensors use thermally matched beads. They are located in opposing arms of a Wheatstone bridge electrical circuit, where the ‘sensitive’ sensor (usually known as the ‘s’ sensor) will react to any combustible gases present, whilst a balancing, ‘inactive’ or ‘non-sensitive’ (n-s) sensor will not. Inactive operation is achieved by either coating the bead with a film of glass or de-activating the catalyst so that it will act only as a compensator for any external temperature or humidity changes.

A further improvement in stable operation can be achieved by the use of poison resistant sensors. These have better resistance to degradation by substances such as Silicones, Sulphur and Lead compounds which can rapidly de-activate (or ‘poison’) other types of catalytic sensor.

Speed of Response

To achieve the necessary requirements of design safety, the catalytic type of sensor has to be mounted in a strong metal housing behind a flame arrestor. This allows the gas/air mixture to diffuse into the housing and on to the hot sensor element, but will prevent the propagation of any flame to the outside atmosphere. The flame arrestor slightly reduces the speed of response of the sensor but, in most cases the electrical output will give a reading in a matter of seconds after gas has been detected. However, because the response curve is considerably flattened as it approaches the final reading, the response time is often specified in terms of the time to reach 90 percent of its final reading and is therefore known as the T90 value. T90 values for catalytic sensors are typically between 20 and 30 seconds.

(N.B. In the USA and some other countries, this value is often quoted as the lower T60 reading and care should therefore be taken when comparing the performance of different sensors).

Calibration

The most common failure in catalytic sensors is performance degradation caused by exposure to certain poisons’. It is therefore essential that any gas monitoring system should not only be calibrated at the time of installation, but also checked regularly and re-calibrated as necessary. Checks must be made using an accurately calibrated standard gas mixture so that the zero and ‘span’ levels can be set correctly on the controller.

Codes of practice such as EN50073:1999 can provide some guidance about the calibration checking frequency and the alarm level settings. Typically, checks should initially be made at weekly intervals but the periods can be extended as operational experience is gained. Where two alarm levels are required, these are normally set at 20-25% LEL for the lower level and 50-55% LEL for the upper level.

Older (and lower cost) systems require two people to check and calibrate, one to expose the sensor to a flow of gas and the other to check the reading shown on the scale of its control unit. Adjustments are then made at the controller to the zero and span potentiometers until the reading exactly matches that of the gas mixture concentration.

Remember that where adjustments have to be made within a flameproof enclosure, the power must first be disconnected and a permit obtained to open the enclosure.

Today, there are a number of ‘one-man’ calibration systems available which allow the calibration procedures to be carried out at the sensor itself. This considerably reduces the time and cost of maintenance, particularly where the sensors are in difficult to get to locations, such as an offshore oil or gas platform. Alternatively, there are now some sensors available which are designed to intrinsically safe standards, and with these it is possible to calibrate the sensors at a convenient place away from the site (in a maintenance depot for instance). Because they are intrinsically safe, it is allowed to freely exchange them with the sensors needing replacement on site, without first shutting down the system for safety.

Maintenance can therefore be carried out on a ‘hot’ system and is very much faster and cheaper than early, conventional systems.

Semiconductor Sensor

Sensors made from semiconducting materials gained considerably in popularity during the late 1980s and at one time appeared to offer the possibility of a universal, low cost gas detector. In the same way as catalytic sensors, they operate by virtue of gas absorption at the surface of a heated oxide. In fact, this is a thin metal-oxide film (usually oxides of the transition metals or heavy metals, such as tin) deposited on a silicon slice by much the same process as is used in the manufacture of computer ‘chips’. Absorption of the sample gas on the oxide surface, followed by catalytic oxidation, results in a change of electrical resistance of the oxide material and can be related to the sample gas concentration. The surface of the sensor is heated to a constant temperature of about 200-250°C, to speed up the rate of reaction and to reduce the effects of ambient temperature changes.

Semiconductor sensors are simple, fairly robust and can be highly sensitive. They have been used with some success in the detection of Hydrogen Sulphide gas, and they are also widely used in the manufacture of inexpensive domestic gas detectors. However, they have been found to be rather unreliable for industrial applications, since they are not very specific to a particular gas and they can be affected by atmospheric temperature and humidity variations. They probably need to be checked more often than other types of sensor, because they have been known to ‘go to sleep’ (i.e. lose sensitivity) unless regularly checked with a gas mixture and they are slow to respond and recover after exposure to an outburst of gas.

Thermal Conductivity

This technique for detecting gas is suitable for the measurement of high (%V/V) concentrations of binary gas mixes. It is mainly used for detecting gases with a thermal conductivity much greater than air e.g. Methane and Hydrogen. Gases with thermal conductivities close to air cannot be detected E.g. Ammonia and Carbon Monoxide. Gases with thermal conductivities less than air are more difficult to detect as water vapour can cause interference E.g. Carbon Dioxide and Butane. Mixtures of two gases in the absence of air can also be measured using this technique.

The heated sensing element is exposed to the sample and the reference element is enclosed in a sealed compartment. If the thermal conductivity of the sample gas is higher than that of the reference, then the temperature of the sensing element decreases. If the thermal conductivity of the sample gas is less than that of the reference then the temperature of the sample element increases. These temperature changes are proportional to the concentration of gas present at the sample element.

Infrared Gas Detector

Many combustible gases have absorption bands in the infrared region of the electromagnetic spectrum of light and the principle of infrared absorption has been used as a laboratory analytical tool for many years. Since the 1980s, however, electronic and optical advances have made it possible to design equipment of sufficiently low power and smaller size to make this technique available for industrial gas detection products as well.

These sensors have a number of important advantages over the catalytic type. They include a very fast speed of response (typically less than 10 seconds), low maintenance and greatly simplified checking, using the self-checking facility of modern micro-processor controlled equipment. They can also be designed to be unaffected by any known ‘poisons’, they are failsafe and they will operate successfully in inert atmospheres, and under a wide range of ambient temperature, pressure and humidity conditions.

The technique operates on the principle of dual wavelength IR absorption, whereby light passes through the sample mixture at two wavelengths, one of which is set at the absorption peak of the gas to be detected, whilst the other is not. The two light sources are pulsed alternatively and guided along a common optical path to emerge via a flameproof ‘window’ and then through the sample gas. The beams are subsequently reflected back again by a retro-reflector, returning once more through the sample and into the unit. Here a detector compares the signal strengths of sample and reference beams and, by subtraction, can give a measure of the gas concentration.

This type of detector can only detect diatomic gas molecules and is therefore unsuitable for the detection of Hydrogen.

Open Path Flammable Infrared Gas Detector

Traditionally, the conventional method of detecting gas leaks was by point detection, using a number of individual sensors to cover an area or perimeter. More recently, however, instruments have become available which make use of infrared and laser technology in the form of a broad beam (or open path) which can cover a distance of several hundred metres. Early open path designs were typically used to complement point detection, however the latest 3rd generation instruments are now often being used as the primary method of detection. Typical applications where they have had considerable success include FPSOs, add jettys, loading/unloading terminals, pipelines, perimeter monitoring, off-shore platforms and LNG (Liquid Natural Gas) storage areas.

Early designs use dual wavelength beams, the first coinciding with the absorption band peak of the target gas and a second reference beam which lies nearby in an unabsorbed area. The instrument continually compares the two signals that are transmitted through the atmosphere, using either the back-scattered radiation from a retroreflector or more commonly in newer designs by means of a separate transmitter and receiver. Any changes in the ratio of the two signals is measured as gas. However, this design is susceptible to interference from fog as different types of fog can positively or negatively affect the ratio of the signals and thereby falsely indicate an upscale gas reading/alarm or downscale gas reading/fault. The latest 3rd generation design uses a double band pass filter that has two reference wavelengths (one either side of the sample) that fully compensates for interference from all types of fog and rain. Other problems associated with older designs have been overcome by the use of coaxial optical design to eliminate false alarms caused by partial obscuration of the beam and the use of xenon flash lamps and solid state detectors making the instruments totally immune to interference from sunlight or other sources of radiation such as flare stacks, arc welding or lightning.

Open path detectors actually measure the total number of gas molecules (i.e. the quantity of gas) within the beam. This value is different to the usual concentration of gas given at a single point and is therefore expressed in terms of LEL meters.

Electrochemical Sensor

Gas specific electrochemical sensors can be used to detect the majority of common toxic gases, including CO, H2S, Cl2, SO2 etc. in a wide variety of safety applications.

Electrochemical sensors are compact, require very little power, exhibit excellent linearity and repeatability and generally have a long life span, typically one to three years. Response times, denoted as T90, i.e. time to reach 90% of the final response, are typically 30-60 seconds and minimum detection limits range from 0.02 to 50ppm depending upon target gas type.

Commercial designs of electrochemical cell are numerous but share many of the common features described below:

Three active gas diffusion electrodes are immersed in a common electrolyte, frequently a concentrated aqueous acid or salt solution, for efficient conduction of ions between the working and counter electrodes.

Depending on the specific cell the target gas is either oxidised or reduced at the surface of the working electrode. This reaction alters the potential of the working electrode relative to the reference electrode. The primary function of the associated electronic driver circuit connected to the cell is to minimise this potential difference by passing current between the working and counter electrodes, the measured current being proportional to the target gas concentration. Gas enters the cell through an external diffusion barrier that is porous to gas but impermeable to liquid.

Many designs incorporate a capillary diffusion barrier to limit the amount of gas contacting the working electrode and thereby maintaining “amperometric” cell operation.

A minimum concentration of Oxygen is required for correct operation of all electrochemical cells, making them unsuitable for certain process monitoring applications. Although the electrolyte contains a certain amount of dissolved Oxygen, enabling short-term detection (minutes) of the target gas in an Oxygen-free environment, it is strongly advised that all calibration gas streams incorporate air as the major component or diluent.

Specificity to the target gas is achieved either by optimisation of the electrochemistry, i.e. choice of catalyst and electrolyte, or else by incorporating filters within the cell which physically absorb or chemically react with certain interferent gas molecules in order to increase target gas specificity. It is important that the appropriate product manual be consulted to understand the effects of potential interferent gases on the cell response.

The necessary inclusion of aqueous electrolytes within electrochemical cells results in a product that is sensitive to environmental conditions of both temperature and humidity. To address this, the patented Surecell™ design incorporates two electrolyte reservoirs that allows for the ‘take up’ and ‘loss’ of electrolyte that occurs in high temperature/high humidity and low temperature/low humidity environments.

Electrochemical sensor life is typically warranted for 2 years, but the actual lifetime frequently exceeds the quoted values. The exceptions to this are Oxygen, Ammonia and Hydrogen Cyanide sensors where components of the cell are necessarily consumed as part of the sensing reaction mechanism.

Chemcassette^®

Chemcassette^® is based on the use of an absorbent strip of filter paper acting as a dry reaction substrate. This performs both as a gas collecting and gas analysing media and it can be used in a continuously operating mode. The system is based on classic colorimetry techniques and is capable of extremely low detection limits for a specific gas. It can be used very successfully for a wide variety of highly toxic substances, including Di-isocyanates, Phosgene, Chlorine, Fluorine and a number of the hydride gases employed in the manufacture of semiconductors.

Detection specificity and sensitivity are achieved through the use of specially formulated chemical reagents, which react only with the sample gas or gases. As sample gas molecules are drawn through the Chemcassette^® with a vacuum pump, they react with the dry chemical reagents and form a coloured stain specific to that gas only. The intensity of this stain is proportionate to the concentration of the reactant gas, ie, the higher the gas concentration, the darker is the stain. By carefully regulating both the sampling interval and the flow rate at which the sample is presented to the Chemcassette^®, detection levels as low as parts-per-billion (ie, 10 -9) can be readily achieved.

Stain intensity is measured with an electro-optical system which reflects light from the surface of the substrate to a photo cell located at an angle to the light source. Then, as a stain develops, this reflected light is attenuated and the reduction of intensity is sensed by the photo detector in the form of an analogue signal. This signal is, in turn, converted to a digital format and then presented as a gas concentration, using an internally-generated calibration curve and an appropriate software library. Chemcassette^® formulations provide a unique detection medium that is not only fast, sensitive and specific, but it is also the only available system which leaves physical evidence (i.e. the stain on the cassette tape) that a gas leak or release has occurred.

Comparison of Gas Detection Techniques

The following Gas Detector references are from sources which provide what ICEweb considers to be the best technical and educational information on the subject. We always acknowledge the author and source. Should there be any issue with ICEweb providing this information, please This email address is being protected from spambots. You need JavaScript enabled to view it. and we will remove it immediately. We also welcome non-commercial technical documents (subject to editorial review) and post them free - ICEweb is a Free Technical Information Website for Instrument, Control, Fire & Gas and SIS Engineers.

 

Gas Detection Technical Design Engineering References for Instrument and Fire & Gas Engineers

Honeywell Analytics Gas Book - This comprehensive handbook is intended to offer a simple guide to anyone considering the use of gas detection equipment. It provides an explanation of both the principles involved and the instrumentation needed for satisfactory protection of personnel, plant and environment. The aim has been to answer as many as possible of the most commonly asked questions about the selection and use of industrial gas detection equipment. Be patient, this document may take a while to download.

At The Heart of Gas Detection Systems - Detecting Hazards - Quite Simple in Principle- Why It Is Worth Knowing More About Gas Detection Sensors - Our sensory organs are often unable to detect airborne hazards, or cannot do so early enough. Toxic or flammable gases and vapours can build up, reaching hazardous concentrations, or there may be insufficient oxygen in the air. Both of these scenarios can have life-threatening consequences. The reliability with which harmful airborne substances can be detected depends to a large extent on the sensors that are used. It is essential for the gas detector and sensor to be adapted perfectly to each other. Hazards must be identified in good time and dependably, and false alarms leading to production downtime and the like must be avoided. You entrust the safety and protection of your personnel, equipment and property to a perfectly working sensor - from Draeger.

Explosion Hazards Mostly Arise from Flammable Gases And Vapours - Instead of avoiding their ignition by explosion protection measures it maybe preferable to detect them before they become ignitable. Depending on the application different measuring principles for the detection of gases and vapours can be used: Catalytic bead sensors, point or open-path infrared sensors - from Draeger. This Covers:

• Preventing potentially explosive atmospheres - primary explosion protection
• Safety relevant data of flammable gases and vapours
• Avoiding effective ignition sources - secondary explosion protection
• Utilisation of gas detection systems reducing the probability of formation of explosive atmospheres
• Pellistor sensors and Infrared sensors
• Proper calibration and sensor positioning of a gas detection system

Gas Detection Handbook - This Gas Detection Handbook from MSA is designed to introduce users to key terms and concepts in gas detection and to serve as a quick reference manual for information such as specific gas properties, exposure limits and other data. The Handbook contains;

• A glossary of essential gas detection terms and abbreviations.
• A summary of key principles in combustible and toxic gas monitoring.
• Reference data-including physical properties and exposure limits for the most commonly monitored gases, in industrial and various other environments.
• A comparison of the most widely-used gas detection technologies.
• A table indicating the gas hazards common to specific applications within major industries.
• A summary of key gas detection instrumentation approvals information, including hazardous locations classification.
• A Sensor Placement Guide, detailing important factors to take into consideration when determining optimum gas sensor placement.

Gas Detection for Offshore Application - Peter Okoh - This is an excellent paper - Release of hazardous and flammable gas is a significant contributor to risk in the offshore oil and gas industry and various types of automatic systems for rapid detection of gas are therefore installed to accentuate the elimination or reduction of the dangerous releases. There are different types of gases which may be released and gas may be released in different environments and under different conditions. Several principles for detecting gas are therefore applied and a variety of types of gas detectors are in use. However, a significant percentage of gas releases remain undetected by the dedicated detectors and hence unaccounted for and uncontrolled. The objectives of this paper are: (1) to present a state-of-the art overview of gas detection in relation to offshore applications, (2) to present an overview of requirements for gas detection in the Norwegian off- shore industry, and (3) to do a comparative study of performance standards for gas detection worldwide. The paper builds on a review of literature, standards and guidelines in relation to gas detection offshore - from Probabilistic Safety Assessment and Management.

Positioning of Gas Detectors at Offshore Installations - Julian André Båfjord - This excellent thesis studies different factors which must be considered when selecting the best suited positions for gas detectors at offshore installations where production of oil and gas takes place and evaluate their degree of impact on the functionality and reliability of the gas detection system. The different factors’ influence on the risk level related to undesired gas releases are discussed as well - from BIBSYS Brage.

Introduction to Gas Detection - The detection of hazardous gases has always been a complex subject and makes choosing an appropriate gas monitoring instrument a difficult task. This excellent introductory chapter from International Sensor Technology covers;

• Analytical Instruments and Monitoring Systems
• Gas Sensors
• Terms, Definitions, and Abbreviations
• Units of Measure for Gas Concentration
• Equations for Deriving Units of Gas Concentration
• Lower Explosive Limit (LEL) or Lower Flammable Limit (LFL)
• Upper Explosive Limit (UEL) or Upper Flammable Limit (UFL)
• Toxic Gases
• Performance Specifications
• Hazardous Locations
• Types of Protection
• Enclosure Classifications For Nonhazardous Areas

Sensor Selection Guide - Electrochemical, Catalytic Bead, Solid State, Infrared and Photoionization Detectors must meet certain criteria to be practical for use in area air quality and safety applications. Some of the basic requirements are detailed in this chapter from International Sensor Technology which also includes a useful look up table. Also detailed are Factors to Consider When Selecting Sensors and Toxic versus Combustible Gas Monitoring.

Gas Detection Technology and Applications - This is a 52 page booklet full of good F&G information.

Fundamentals of Combustible Gas Detection - A 36 page technical Guide on the Characteristics of Combustible Gases and Applicable Detection Technologies - from General Monitors.

Why is Hydrogen Leak Detection Important? - Hydrogen is one of the three most dangerous combustible gases; the other two are Acetylene and Carbon Disulphide. These gases are particularly dangerous as they need very small ignition energy to ignite them (the minimum ignition energy of Hydrogen is just 40uJ) and for this reason have a separate gas group IIC as per the European standard - from Honeywell Analytics.

Gas Leak Detection for Boiler Rooms in Commercial and Industrial Property - Natural gas is one of the most widely used fuels for heating commercial and industrial property. In the event of an undetected leak it can present an explosive risk leading to structural damage, the loss of life or an expensive waste of fuel. Most boiler plant rooms are visited infrequently and therefore any leak will go undetected. An automatic gas detection system will provide early warning of a gas release during unmanned periods - from Honeywell Analytics.

List of Detectable Gases and Vapours - This list whilst being associated with Drager Equipment provides comprehensive information on gases and Vapours, Composition, LEL etc.

Infrared (IR) Gas Detection Technology is Keeping Field Personnel Safer - LED-Driven Infrared Sensors: Shining New Light on LEL Gas Measurement for Oil and Gas and Confined Space Entry Applications - Oil and gas production and work in confined spaces exposes field personnel to a variety of toxic and explosive gases in every day drilling, processing, transport and municipal operations. Explosive gas build-ups can endanger not only the workers nearby, but also a widespread area beyond the working area, making fast, accurate measurement of combustible gases below LEL levels critical to maintaining safety. Today, there are two main sensor technologies used for detecting explosive gases: catalytic bead and infrared - from Gas Clip Technologies.

Monitoring Flammable Vapours and Gases - This paper gives a different approach whilst still covering the more conventional techniques - from Control Instruments Corporation

Measuring Solvent, Fuel and Volatile Organic Compounds (VOC) Vapours in the Workplace Environment - Robert E. Henderson - Solvent, fuel and many other VOC vapours are pervasively common in many workplace environments. Most have surprisingly low occupational exposure limits. For most VOCs, long before you reach a concentration sufficient to register on a combustible gas indicator, you will have easily exceeded the toxic exposure limits for the contaminant - from BW Technologies.

The following paper is from IDC Technologies - Specialists In Engineering Courses & Training

Introduction to Functional Safety Standards in Gas Detection - Preeju Anirudhan - Draeger Safety Pacific Pty Ltd - The objective of this session is to create awareness on gas detection and the various technologies used in gas detection, including the role of gas detectors in risk reduction. This paper covers gas dispersion & placement of sensors and the considerations that must be given while deciding sensor technology, sensor placement and maintenance of the detectors, with a life-cycle approach. It also discusses the various standards applicable in the field of gas detection, functional safety applications, including standards applicable to plants & projects. In addition it addresses common mistakes due to incorrect use of standards, controller and precautions that must be taken while using PLC’s and the limitations of using PLC’s for gas detection applications - from the IDC Safety Control Systems Conference 2015.

 

Comparison of Gas Detection Technologies

It is important to compare Gas Detection technologies because there are different advantages and disadvantages to each technology and application. For instance Infrared will not work when one requires to measure Hydrogen. Catalytic Detectors may be "poisoned" and also are very maintenance prone. Thus all Instrument and Fire & Gas Engineers must be aware of the differences and be able to make a correct decision as to which one to utilise.

The following references are very useful.

Combustible Gas Detector Sensor Drift: Catalytic vs Infrared - Kelly Rollick, Allan Roczko, and Leslie Mitchell - Catalytic bead combustible sensor technology, used for decades to measure combustible gas concentrations, dates back to the 1830s. The infrared spectrum was discovered in 1800. The 1950s saw a surge in infrared spectrum use for many technological applications, including gas detection. These distinct gas detection technologies offer advantages and disadvantages, with conditions determining the better choice for specific applications - from ISA

Detecting Combustible Gases and Vapours - Catalytic Bead or Infrared? - Anyone wishing to detect combustible gases and vapours is generally faced with the following important questions: Is it better to use the more economical catalytic bead sensors or the longer life infrared sensors? What are the advantages and disadvantages of each? What points are important to note? Are there certain applications which are better suited to one or the other method? This article aims to provide answers to the questions most frequently asked in this context - from Draeger Australia.

Comparison of Gas Detection Technologies - Covers Electrochemical Sensors, Metal Oxide Semiconductor (MOS) Sensors, Photoacoustic Sensors and Infrared Sensors - from OI Analytical.

Combustible Gas Safety Monitoring: Infrared vs. Catalytic Gas Detectors - A booklet which advises when to use the various technologies - from General Monitors.

 

Maintenance of Gas Detection Systems

Ask the Gas Detection Experts - Although certain principles of gas detection require less maintenance than others, the calibration and servicing frequency of gas detection equipment is largely dependent on the environment and application where it is being used. Weather conditions, dust, dirt, water and even the types of compounds being used nearby can have an effect on the performance of equipment and influence the frequency of maintenance activities.

Placement & Maintenance of Fixed-Point Gas Monitoring Systems - Matt Thiel - Gas detectors are typically exposed to some of the harshest conditions. They are placed in areas where they are exposed to extreme weather, dust, dirt, oil, and debris. These products are designed to operate in these conditions, but the instruments should be inspected on a regular basis - from Industrial Scientific Corporation.

Maintaining Catalytic Combustible Gas Detectors - In oil / gas and petrochemical production, refining, transportation and distribution facilities, safety is always of paramount concern due to the combustible nature of hydrocarbon-based products. All such facilities must install combustible gas monitoring systems to protect people and equipment. After selecting and installing catalytic bead sensors, maintenance is an ongoing task that requires periodic attention to ensure a safe work environment - from General Monitors.

Calibration Could Save Your Life - A gas detector is a safety device. A properly functioning gas detector could be the difference between life and death. Making sure such a device is working properly on a regular basis should, without question, be a part of a scheduled maintenance program - from CETCI Magazine.

 

Planning and Designing Gas Detection Systems

New Separate and Comprehensive Page! - The Planning and Designing of Gas Detection Systems should only be undertaken by Competent and Experienced Instrument or Fire and Gas Engineers. ICEweb's Planning and Designing of Gas Detection Systems - for Instrument and Fire & Gas Engineers page gives some useful technical advice on this. It also has a reference source which provides further excellent engineering information on the subject - from Industrial Scientific Corporation.

 

Addressable Gas Detectors

Addressable Gas Detection Systems - Analogue Gas detection systems serve many applications and are installed across the whole spectrum of industry. These systems have provided solutions to monitoring problems for many years gathering information on changing levels of gas for trending and logging applications or as part of safety warning/shutdown systems for Toxic and Flammable gas applications. From Extronics.

 

Air Duct Gas Detection

Monitoring of Air Ducts - Some really useful information here about gas detection monitoring in air ducts - thanks to Simrad Optronics and PROdetec.

Gas Detection in Air Intakes - When it comes to monitoring of ventilation air, at air intakes, in ventilation ducts or at ventilation outlets, the trend has been towards lower trip levels and/or faster response times. This product information discusses these issues in order to help choosing the right detector for the task - from Simrad Optronics and PROdetec.

Detecting Combustible and Toxic Gases in HVAC Ducts - Air handling systems are used throughout industry to provide comfort and health in manned areas. Nevertheless, if unprotected, facility ventilation systems can transport combustible and toxic gases from a source area to other parts of the building, bringing the dangerous substances into non-hazardous areas, like control rooms, living quarters, electrical switch rooms, and equipment rooms. Because of the potential for the inadvertent transport of dangerous substances, government agencies, industry groups and many leading companies have established procedures for exhaust/ventilation system safety. One important element in the protection of these systems is gas detection - from General Monitors.

 

Catalytic Combustible Gas Detectors

Maintaining Catalytic Combustible Gas Detectors - Even the best of safety monitoring equipment requires periodic inspection. There must be a maintenance plan in place with documented procedures, a regular schedule of inspections, repair or replacement activity as necessary, problem reporting, etc. It is important to train employees to know when inspection is necessary and what type of maintenance procedures must be performed on a specific type or model of gas detector - from General Monitors.

Catalytic Sensors - This Article covers Principle of Operation, Applications, Relative Sensitivity and Restrictions on Use - from Sensitron.

Understanding Catalytic LEL Combustible Gas Sensor Performance - In spite of the millions of combustible sensor equipped atmospheric monitors in service around the world, there is still a lot of misinformation and misunderstanding when it comes to the performance characteristics and limitations of this very important type of sensor. Understanding how combustible sensors detect gas is critical to correctly interpreting readings, and avoiding misuse of instruments that include this type of sensor.

Catalytic Combustible Gas Sensors - Catalytic bead sensors are used primarily to detect combustible gases. They have been in use for more than 50 years. Initially, these sensors were used for monitoring gas in coal mines, where they replaced canaries that had been used for a long period of time. The sensor itself is quite simple in design and is easy to manufacture. In its simplest form, as used in the original design, it was comprised of a single platinum wire. Catalytic bead sensors were produced all over the world by a large number of different manufacturers, but the performance and reliability of these sensors varied widely among these various manufacturers - from International Sensor Technology.

 

Calibrating Gas Sensors

Gas Sensor Calibration - Gas sensors need to be calibrated and periodically checked to ensure sensor accuracy and system integrity. It is important to install stationary sensors in locations where the calibration can be performed easily. The intervals between calibration can be different from sensor to sensor. Generally, the manufacturer of the sensor will recommend a time interval between calibration. However, it is good general practice to check the sensor more closely during the first 30 days after installation. During this period, it is possible to observe how well the sensor is adapting to its new environment - from International Sensor Technology.

 

Calibration Gas for Gas Detectors

Do Calibration Gases Have a Shelf Life? - Calibration is a vital and necessary step to ensuring the proper performance of any gas detector. The calibration process requires use of a known concentration of test gas, also known as span gas or calibration gas. Use of incorrect or expired calibration gas can result in improper calibration. This can result in unsafe operation, as well as improper diagnosis of instrument malfunction. This article will focus on disposable (non-refillable) calibration gas cylinders for both reactive and non-reactive gases - from Control Equipment.

Gas Calibration: Methane or Pentane? - Choosing the incorrect gas to calibrate your detector will make the readings inaccurate and potentially unsafe. This article explains which gas to use in order to ensure accurate and safe readings - from CAC.

 

Open Path Infra Red Gas Detectors

ICEweb has a Technical Information Page for Instrument and Fire & Gas Engineers dedicated to Open Path Gas Detectors, it covers Infra Red Line of Sight (Open Path) and Point Detectors Principle of Operation, Technology, Calibration and more!

The Benefits of IR Gas Detection for Oil and Gas Applications - Gem Bayless - Gas detection has been through a number of evolutions since the birth of the industry over 50 years ago. A major milestone in its history has been the introduction of Infrared (IR) gas detection, which uses a Hydrocarbon gases ability to absorb IR light at a pre-determined wavelength. Thanks to its notable value, which includes a fast speed of response (typically T90 in less than 5 seconds), fail-to-safety operation, immunity to poisons and ability to work in inert atmospheres, IR detection is fast becoming a popular method of detection - particularly within the oil, gas and petrochemical industries - from Honeywell and PetroOnline.

Gas Detection Infrared Sensors Broaden Scope of Platform Gas Analysis - Jeff Markley - Catalytic detectors reveal the presence of combustible gases through a change in the resistance of the embedded coil - but their sensitivity can be affected by airborne contaminants. Infrared sensors allow open path detectors to detect gas up to 200 metres away - from Honeywell Analytics.

Reducing Costs and Enhancing Safety with Open Path Infrared (IR) Gas Detection - It is fair to say that Infrared (IR) technology has revolutionised the gas detection market, providing a principle of detection that offers many tangible benefits in terms of performance, functionality and reduced ongoing costs. Since IR’s introduction into gas detection during the late 1970s, a variety of principles have subsequently emerged, the most impacting of which has been Open Path. This is a detection technique that allows gas to be monitored across a large range. Unlike a single Point IR device, an Open Path detector usually has two components with a beam of IR light between them, allowing this type of device to detect a gas cloud that drifts into the beam. This configuration provides the instant benefit of an increased chance of detecting a gas leak. Designed to monitor a diverse variety of Hydrocarbon gases, Open Path IR has a number of key benefits that add real value, when compared to solutions like catalytic bead detection. It is essential to consider the build, configuration and value of the Open Path devices currently available, when selecting a system, as they can vary considerably in terms of performance capability and ability to reduce ongoing costs - from Honeywell Analytics.

 

Gas Detection Certification

From Singing to Sensing - IECEx Certifies Modern Gas Detectors and Sensors - Like a Canary in a Coal Mine - The use of canaries as gas detectors had been a mining tradition in the UK since 1911. Toxic gases such as carbon monoxide, carbon dioxide or methane in the mine would kill the bird before affecting the miners. Because canaries tend to sing much of the time, they would stop singing prior to succumbing to the gas, so alerting miners to the danger. As reliable as canaries might have been, the switch to electronic gas detectors actually made sense and brought greater safety. Technologies are evolving constantly and modern gas detection devices are state-of-the-art, extremely sophisticated devices that use sensors to identify potentially hazardous gas leaks. They are usually part of larger safety systems that can be found in a wide variety of locations such as mines, oil rigs, refineries, paper mills and industrial / waste water treatment plants. They are also widely used by firefighters. These devices often interface with control systems so that a process can be shut down automatically in dangerous situations. This is well worth a read - from IECEX.

 

Gas Detection using Laser Technology

Gas Detection using Lasers - A good tutorial on this new technology from Boreal Laser.

 

Gas Detection using Photoacoustic Infrared Technology

Photoacoustic Infrared Technology - is the newest method of gas detection. It enables gases to be detected at extremely low levels due to its inherent stability and reduced cross-sensitivity - Thanks to MSA.

 

Gas Detection in Gas Turbines and Compressor Stations

Fire and Gas Detection for Gas Turbines - Modern gas turbines are designed to burn light oils (Naphtha) or natural gas. Fuels and the lubricating oils along with cooling agents like hydrogen add-up to a high degree of hazard potential. For these reasons a multiple line of defence has to be established to guaranty protection against fire and explosion risks. Gas detection instruments and optical fire detectors are the central element in the protection systems - from Draeger Australia.

Detecting Combustible Gas Leaks in Compressor Stations - In gas compressor stations, there is a high risk of fire and explosion due to a combination of intense heat, pressure and vibration. Gas detection solutions help to maintain safety in gas compressor stations. Ultrasonic, Infrared and Catalytic Bead gas detectors can be used alone or in integrated systems to help stabilize hazardous environments - from General Monitors.

 

Gas Detection Standards

AS/NZS 60079.29.4:2011 - Explosive Atmospheres - Gas Detectors - Performance requirements of open path detectors for flammable gases.The objective of this Standard is to establish the specific requirements for design, construction and performance testing of electrical equipment for open path detection of flammable gases and vapours. It is complementary to AS/NZS 60079.29.1, which applies to the other detection techniques available for this purpose. It is intended to be read in conjunction with AS/NZS 60079.0 for its electrical protection. See a preview here.

Survey of Standards - Related to Gas Detectors - Bill Crosley and Simon Pate- What are the key standards for gas detectors? This paper lists the main world-area standards to which protection types are tested and certified. For combustible gas detector criteria, there is little to differentiate between FM 6310, 6320 (used mainly in the US) and the CSA C22.2 #152 (used mainly in Canada). Both are closely related to ANSI/ISA 12.13.01-2000. In those countries (mostly in Europe) that have adopted the IEC standards. The IEC 60079-29 Series contains not only the hazardous locations requirements but also the gas detection performance requirements for both point and open path combustible gas detectors. In offshore toxic gas applications, the ISA standard is generally the defacto global standard for most world areas. Standards EN 50402, EN 45544, and EN 50104 are used in Europe and other world areas. Gas detectors are a critical part of the overall safety system. Therefore, all standards require the gas detector, the controller, and the output for the performance approval. Output is often the annunciation device. Be aware, though, that in many applications when a gas detector is connected to the process automation system it is not in full compliance with the requirements of FM6310,20 based on ANSI/ISA 12.13.01 or IEC60079-29–the process automation systems are not evaluated against these standards.

IEC 60079-29-4 - Explosive atmospheres, Part 29-4: Gas detectors-Performance requirements of open path detectors for flammable gases.

 

Portable Gas Detection

Plant Safety Engineers take Aim at a Wireless Future - Dr.Patrick Hogan - Equipping the mobile worker with a personal gas monitor that not only can monitor a range of hazardous gases, but also report the worker’s exact location, continuously, in real time-over a wireless communications grid-represents one small step forward for today’s control room operator, yet one giant leap forward for plant safety - thanks to Honeywell Analytics and HazardEx.

Working Safely in Confined Spaces - Confined spaces pose various hazards for operators and can be found in a wide variety of industries and applications. A confined space can be defined by a number of factors; the space itself must be large enough for a worker to enter but is not suitable for continuous worker occupancy. A confined space is also defined as having limited openings for entry and exit. Examples of confined spaces found in industry include aircraft fuel tanks, underground utility vaults and wine fermentation tanks. Due to their small size, gas hazards can quickly build up in confined space environments. Some confined spaces may require permits to enter, owing to the fact that they contain potentially hazardous atmospheres or materials that have the potential for engulfment. Inwardly sloping walls or floors can also pose dangers, because they reduce the volume of the space, and may also require a permit to enter. Regardless of whether the area is permit required or not, all confined spaces should be treated as potential hazards - from Honeywell Analytics.

 

Portable Gas Detection Bump Testing

New Regulation Highlights Importance of Bump Testing - Bump testing is a quick and essential test that ensures a portable gas detector is working properly. It involves exposing the device to a known concentration of gas/gases and checking its response and whether it alarms within its pre-defi ned parameters. When it comes to working with dangerous gases, a bump test really can mean the difference between life and death - from Honeywell Analytics.

 

Photoionization Detectors

Photoionization Detectors - The photoionization detector (PID) utilises ultraviolet light to ionize gas molecules, and is commonly employed in the detection of volatile organic compounds (VOCs) - this comprehensive chapter from International Sensor Technologies covers;

• Principle of Operation
• Characteristics
• Applications

 

Toxic Gas Monitors

Electrochemical Sensors - Electrochemical sensors operate by reacting with the gas of interest and producing an electrical signal proportional to the gas concentration. A typical electrochemical sensor consists of a sensing electrode (or working electrode), and a counter electrode separated by a thin layer of electrolyte. This comprehensive chapter from International Sensor Technology provides an excellent overview of these sensors which are predominately used for Toxic Gas Monitors.

Simtronics Enhances GD1 Open-Path Toxic Laser Gas Detector Performance and Maximum Distance - Simtronics GD1 Laser Open-Path Detector has been enhanced with a stronger signal which increases the path length distance between the detector and transmitter from 50m to 75m; an increase of 50%. In addition, the considerably improved signal strength has increased the detector’s robustness and performance especially in extreme weather conditions such as ice and sand storms - from ProDetec.

An introduction to Toxic Gas Monitors - Industrial plants that manufacture chemicals, fertilizers, petroleum products, or, facilities that produce oil & gas, have to handle various toxic chemicals in their day to day operations. Many of these toxic chemicals are in the form of gases or vapors. This article will give a brief overview of the various kinds of toxic gas detectors used to detect these poisonous materials - From Abhisam Software.

 

Ultrasonic Gas Leak Detection

Ultrasonic Leak Detection - The First Stage in Gas Detection - These sensors will detect gas at‘the speed of sound’ and do not need to be in the gas cloud to operate successfully. Ultrasonic gas detectors have been designed to detect pressure gas leaks from all gases, this includes the 35% of Hydrocarbon Leaks which go undetected in the North Sea (Source UK HSE) - thanks to PROdetec and Emerson Process Management.

Ultrasonic Detection Overview - Ultrasonic (acoustic) gas leak detection technology functions through the constant monitoring of wide areas by advanced acoustic sensors specially tuned to process ultrasound emitted from pressurized gas leaks. This detection technology has several advantages (a) It does not have to wait until a gas concentration has accumulated to potentially dangerous concentrations and (b) It does not require a gas cloud to eventually make physical contact with a sensor, and the response is instantaneous for all gas types - from Emerson Process Management.

Ultrasonic (Acoustic) Gas Leak Detection Technology - Ultrasonic (acoustic) gas leak detection technology works by listening for ultrasound emitted from pressurised gas leaks. Instead of measuring a concentration level in LEL as traditional gas detectors (point and open path detectors) the ultrasonic gas leak detectors raise an instant on/off alarm if a leak is detected. The ultrasonic gas leak detectors do not have to wait until the gas concentration has accumulated to a potentially dangerous gas cloud, they react instantaneously. This means that unlike traditional gas detectors, ultrasonic detectors can detect gas leaks at the speed of sound without being affected by wind directions or gas dilution. Instead of measuring a concentration level in LEL, the ultrasonic (acoustic) gas leak detection method is based on the so-called leak rate. This makes detection more reliable and efficient as it is possible to verify the performance of the detection system - This link also includes a case history, detection coverage, installation practice, background noise, gas leak definition and frequently asked questions - from Gassonic.

Technology Status Report on Natural Gas Leak Detection in Pipelines - The reliable and timely detection of failure of any part of the pipeline is critical to ensure the reliability of the natural gas infrastructure. This report reviews the current status of the technology for leak detection from the natural gas pipelines. The first part briefly reviews various leak detection methods used in the natural gas pipelines. The second part reviews the optical methods used for natural gas leak detection, and the final part reviews the potential sensors that can be used with optical methods.

Health and Safety

The following are useful articles on health and safety for personal use.

Decommissioning Chemical Plants - A Proven Roadmap - The current economic and socio-political environment has made product lifecycles of chemicals much shorter. Also cost pressures, regulatory pressures, influence of non-state actors and changing market geographies, mean that manufacturing plants (examples are chemical process plants, Oil & Gas facilities, hydrocarbon processing plants and similar) need to be shuffled around, shut down or shifted at a much higher frequency than in earlier years. This article is a primer on how company managements can handle this without getting overwhelmed by the complexities of these projects. This can happen because quite a few company managements may be very skilled and versatile when setting up new plants, but may be inexperienced while doing the reverse - from Abhisam Software.

Mounting Evidence that Carbon Nanotubes May be the New Asbestos - Carbon nanotubes - thin, hollow cylinders made of carbon atoms - look very much like asbestos. In 2004, the United Kingdom’s Royal Society and risk specialists at the world’s second largest reinsurance agent Swiss Re warned that once in our lungs, nanotubes may also behave like asbestos. Since then, a series of experiments have demonstrated that when introduced into the lungs of rodents, carbon nanotubes cause inflammation, granuloma development, fibrosis, artery ‘plaque’ responsible for heart attacks and DNA damage. Two independent studies have shown that carbon nanotubes can also cause the onset of mesothelioma - cancer previously thought to be only associated with asbestos exposure. Unfortunately, despite mounting evidence of the asbestos-like dangers of carbon nanotubes, their commercial use is also growing rapidly - in sports goods, car and aeroplane parts, reinforced plastics and electronics - from Friends of the Earth Australia.

A desktop based Incident Recording, Reporting and Management Software Tool - This free tool allows the recording and management of incidents and accidents, identifying trends using integrated filtering and reporting tools. It also includes automatic creation of the UK government's required standard RIDDOR incident report - From SHE Software Limited.

FOOD FOR THOUGHT - There is a bank that credits your account each morning with $86,400. It carries over no balance from day to day. Every evening deletes whatever part of the balance you failed to use during the day.

What would you do? Draw out ALL OF IT, ofcourse!!!! Each of us has such a bank. Its name is TIME.

• Every morning, it credits you with 86,400 seconds.
• Every night it writes off, as lost, whatever of this you have failed to invest to good purpose. It carries over no balance. It allows no overdraft.
• Each day it opens a new account for you.
• Each night it burns the remains of the day.
• If you fail to use the day's deposits, the loss is yours.
• There is no going back. There is no drawing against the "tomorrow."
• You must live in the present on today's deposits. Invest it so as to get from it the utmost in health, happiness, and success!

The clock is running. Make the most of today. Treasure every moment that you have!

Treasure it more because you shared it with someone special, special enough to spend your time.
And remember that time waits for no one.

Yesterday is history. Tomorrow is a mystery.

Today is a gift. That's why it's called the present!!!

US Chemical Hazard and Safety Investigation Board Links

Safety publications
Video Archive

Safety information - Energy Safety in Western Australia publishes a range of informational brochures related to safe use of electricity and gas in and around the home as well as in the workplace.

WARNING: HOTELS COULD BE HAZARDOUS TO YOUR HEALTH ... by Captain RH Kauffman, Los Angeles County Fire Department - Have you ever been in a hotel during a fire? It’s a frightening experience, and you should start thinking about it.

Most Projects Fail because Preliminary Engineering was not done!

Here are the first steps to success!

Clearly Defined Requirements.

The Preliminary Engineering Proposal Presented by:

INX.INC

Preliminary engineering consists of three parts:

1. Define the process by generating an ISA standard P&I diagram of all necessary equipment. This documentation will then be used as the media for defining the control system. It will be used to develop the required scope of work.

2. Meet with operations and maintenance personnel to create an outline of the sequence of operation. This would include any accommodations necessary to support existing equipment that would be integrated into the new modernized control scheme.

3. Create a detailed specification that includes the systems architecture and controls hardware necessary to accomplish the control and operating configuration defined by parts 1 and 2.

Preliminary Engineering Detailed Scope of Work

• Perform field survey and define impact on existing systems.
• Develop system block diagram drawing detailing systems architecture.
• Develop ISA P&I drawing of system, compile instrumentation and I / O list.
• Specify motor controls and determine power distribution requirements.
• Create sequence of operation and develop specifications for safety and backup requirements.
• Create Interface display screens, operator console layouts and Human to Machine Interface.
• Specify software documentation and crash recovery standards.
• Develop a detailed controls hardware schedule and packaging scheme.
• Specify installation logistics and timing.
• Develop training requirements and preliminary schedule.

Planning and Designing Gas Detection Systems – for Instrument and Fire & Gas Engineers

There is a Massive amount of Technical Engineering Information for Instrument and Fire & Gas Engineers on this page - so make life easy and Go the Subject Area that you are interested in:- Gas Detector Selection | Positioning Gas Detectors | Planning and Designing Gas Detection | Fire and Gas Detection Mapping | Conversions for Gas Detection | Gas Detection Sensor Selection Guide | Standards for Gas Detector Location | Managing Hazardous Areas Effectively by using Gas Monitors .

Instrument and Fire & Gas Engineers have to consider many design aspects to consider when planning and designing detection systems. This includes;

 

Gas Detector Selection

The Engineer has to consider:

• The gas to be measured, is it noxious, explosive or both?
• Have the potential sources of leakage been determined in conjunction with the Process Engineer and as part of the Hazard and Operability (HAZOP) or Control Systems Hazards and Operability (CHAZOP) studies? It is necessary to ensure that there are no areas which are unmonitored especially small pockets at both high and low levels.
• The choice of Positioning Strategy. Are point detectors only required or is a hybrid approach (a combination of both types of point and Line of Sight Infrared needed to achieve the necessary coverage?
• Do you require point (spot), area or fence monitoring?
• The number of sensors, ensure that failure, or maintenance removal of an individual sensor does not compromise the safety of the area being monitored. Duplication (or triplication) of sensors and control apparatus may be required for continuous monitoring and to prevent false alarms.^{1 From the UKHSE}
• What Measurement Technique is required? For Toxic Gases in lower concentrations Electrochemical types are used. Catalytic gas detectors are used for point detection or can be positioned in a grid to ensure wider coverage. Infrared (IR) gas detectors are used for both point and line of sight applications. They are low maintenance devices.
• What are the various advantages and disadvantages associated with the different types of gas detectors?
• Is an aspirated system required? Aspiration systems are used where it is not possible to install gas detectors directly or natural diffusion as a sampling method is assessed to be slow. In many cases a faster response is needed, and the sample is transported to the sensor using a sampling pump. This is called aspirated or extractive sampling.
• What voting strategy is required for the F&G system, 1001, 1002, 2003 etc. These voting strategies are used to ensure that false alarms do not cause false alerts or shutdown.
• What Alert and Shutdown Levels are required? This is generally determined by the operator in line with the associated safety case. A common setting is Low alarm = 20% LEL, High alarm = 40% LEL, High-High alarm = 60% LEL. Although some operators are more conservative and set LEL Low = 10% and LEL High =20%.
• There are also Infrared Cloud Cameras available, this again enhances the overall safety of the plant.

 

Positioning Gas Detectors

The following should be considered;

• Coverage Density - Should there be a large number of potential leak sources (typically in oil and gas package equipment) a good starting density is a spacing of 5 metres between gas detectors.
• Vapours from combustible liquids are generally heavier than air and will collect close to the ground, hence gas detectors should be positioned cloe to the ground. LPG falls into this category.
• Unless they are cryogenic (very cold) three combustible gases are lighter than air, these are hydrogen, ammonia and methane. As a result detectors need to be sited where gases can accumulate in ceiling voids etc.
• Where forced ventilation is used eg., pressurised areas, the gas detectors should be sited at the inlet and in the ducting, normally these are voted in a 2003 configuration. If point type gas detectors are used for areas distant from the inlet it is important to ensure that there are at least three gas detectors between the furthest potential leak source and the air extract. Any design must consider the reaction time and time needed for the executive action to take effect.
• In the case of toxic gases which are heavier than air monitor them around head breathing zone.

 

Planning and Designing Gas Detection -Technical Engineering References for Instrument and Fire & Gas Design Engineers

The following Planning and Designing Gas Detector references are from sources which provide what ICEweb considers to be the best technical and educational information on the subject. We always acknowledge the author and source. Should there be any issue with ICEweb providing this information, please This email address is being protected from spambots. You need JavaScript enabled to view it. and we will remove it immediately. We also welcome non-commercial technical documents (subject to editorial review) and post them free. - ICEweb is a Free Technical Information Website for Instrument, Control, Fire & Gas and SIS Engineers. 

The Planning and Designing of Gas Detection Systems should only be undertaken by Competent and Experienced Instrument or Fire and Gas Engineers. This page gives some useful technical advice on this..

Further Excellent Planning and Designing Gas Detection -Technical Engineering References from around the world follow; How to Manage.

 

Planning and Designing Gas Detection Systems

Planning and Designing Gas Detection Systems - This paper has a wealth of questions, answers, positioning tips etc, from the ISA and InTech it is well worth a read.

Planning of Gas Detection Systems - This brochure is a guide for the planner and installer of gas detection systems. Whilst it is written around Polytron gas detection systems it gives a number of answers for recurring questions emerging during the installation of typical sytems - from Draeger Australia.

Planning and Designing Gas Detection Systems - With a grasp of gas sensor basics, and a methodical plan for installing the detectors, you can build a system smart enough to save your life - Wolfgang Jessel - from Draeger Australia.

Positioning of Sensors Guidelines - The problem for gas detection systems in general , for 95% of installations there are no precise guidelines , either national or international, that could be followed to determine the number, spacing and positioning of gas detectors for a given industrial installation. This paper addresses this issue - from Draeger Australia.

Performance Based Gas Detection System Design for Hydrocarbon Storage Tank Systems - Srinivasan N. Ganesan and Edward M. Marszal - The design of hydrocarbon gas detection systems using risk analysis methods is drawing a lot of attention because industry experts have come to a consensus that design codes used in traditional gas detection system design work are not sufficient for open door process areas having serious hazards, such as fire, flammable gas and toxic gas. The ISA Technical Report TR 84.00.07 provides guidelines for the design of fire and gas systems in unenclosed process areas in accordance with the principles given in IEC 61511 standards. This paper presents an overview of the design of gas detection systems using risk assessment methods that are described in the ISA technical report. These methods are statistical in nature and are used to assign and verify targets for the performance metrics (detector coverage and safety availability) of gas detection systems. This paper also provides an overview of the performance based safety life cycle of gas detection systems from conceptual design stage to operations and maintenance- from isssource.com.

Gas Detection Reference Guide - This excellent comprehensive design guide from Scott Safety covers;

• System Architecture and Application, Designing a Gas Detection System, Industrial Hazards, Common Hazards by Industry, Fixed vs. Portable Detection, Warnings, Alarms and Response Functions.
• Sensor technology including; Catalytic Bead Sensors, Infrared Sensors, Electrochemical Sensors, Photo Ionization Detector, Metal Oxide Semiconductor Sensors, Sensor Performance Factors and Flame Detection.
• Glossary of gas detection terms.

Key Concepts in Gas Detection - A Guide to Understanding Today’s Gas Detection Technology - Gas-detection systems are important front-line watch dogs, and provide many process plants with early notification of dangerous releases. Proper design and layout is critical to the functionality of these systems, but poses a challenge for many users since little standardized guidance is available. A qualified safety professional should be involved in all ultimate design decisions. When designing a gas-detection installation, the user must remember that gas detection is only one part of a facility’s comprehensive safety management plan. To be most useful during facility operation, monitoring system users should address not only how many sensors are required and where they will go, but also how the real-time data provided by these devices can be used to improve the overall safety of the plant and its workers – from Scott Health and Safety.

Guide to Sensor Selection and Placement - This is a useful concise guide for Gas Detector Sensor Selection and Placement - from MSA.

Fundamentals of Combustible Gas Detection - A Guide to the Characteristics of Combustible Gases and Applicable Detection Technologies - from General Monitors.

Diversified Technologies for Fixed Gas Detection - Edward Naranjo and Gregory A. Neethling - Over the years, a variety of gas detection technologies have been developed for the oil, gas, and chemical process industries. The advent of embedded electronics, sophisticated firmware, new materials, and spectral techniques has prompted remarkable improvements in detection. In many cases, technology development proceeds through parallel routes with each technology staking its own specialist market. Catalytic bead sensors and infrared detectors are two examples of conventional sensing methods with wide customer acceptance. Likewise, comparatively newer technologies like open path, gas cloud imaging, and ultrasonic gas leak detection have made inroads into the safety instrumentation market, not due to their novelty, but because they solve customers’ problems like no technology before them. In such a world of competing solutions, it is tempting to think single technologies will provide answers to most industry challenges. Offshore platforms, onshore terminals, gas compressor stations, and other facilities, however, are complex environments no single type of detector is bound to cover completely. Experience has shown it is in fact the combination of gas detection schemes that provide the enhanced level of safety that customers demand - from General Monitors.

Hydrogen Detection in Oil Refineries - This white paper offers a practical approach for the deployment of fire and gas detectors that maximizes detection efficiency. The approach is based on the notion that any one detection technique cannot respond to all hazardous events and consequently, the risk of detection failure is reduced by deploying devices that have different strengths and limitations - from General Monitors.

Combustible Gas Safety Monitoring: Infrared vs. Catalytic Gas Detectors - When designing a combustible gas safety monitoring system for oil/gas, petrochemical or other applications, how do you decide whether to use infrared or catalytic gas detector technology? Both sensing technologies have their advantages dependent upon your application’s specific requirements. A thorough analysis of your application’s unique field environment is needed to ensure optimal performance, safety, reliability and cost-effectiveness. A quick decision, of course, can lead to poor detector choices as well as safety, performance, maintenance, and life-cycle cost consequences - from General Monitors.

Gas Detection Knowledge Base - Many useful articles on Gas Detection here - from Interscan Corporation.

Interfering Gases - No analytical method is completely specific. Gases present in the environment, other than the "target" gas of measurement, may affect instrument response. Interferences are not necessarily linear, and may also exhibit time dependent characteristics - from Interscan Corporation.

4-20mA Transmitter Wiring - Transmitters are available with a wide variety of signal outputs. The 4-20mA analogue signal is by far the most commonly used in industrial applications. Several physical 4-20mA wiring options exist. This guidance note aims to outline these options.

 

Fire and Gas Detection Mapping

Fire and Gas Detection Mapping - Computer Aided Design to Increase Safety and Reduce Cost - Kevin Keefe - Using highly developed assessment methods together with custom software the flame detection assessment, gas detection assessment and heat detection assessment packages are able to review and assess arrangements from initial designs through construction and onto existing installation. The assessments are used to optimise and validate designs and maybe used in formal safety studies – from Micropack .

Mapping Fixed Gas Detectors and Flame Detectors - Bryon Gordon - Early detection of gas leaks and flames can help prevent the escalation of dangerous incidents; therefore, safety engineers must design and implement the most effective detection system possible. Engineers pour over flame and gas detector spec sheets, and they consider safety manufacturer certifications. But high-quality detectors that are improperly placed might not meet detection goals. Safety experts have long known that wise placement of the devices into a specific application leads to effective detection coverage, which in turn leads to the best scenario for successful mitigation. Yet UK Health and Safety Executive (HSE) statistics indicated that 40% of major gas releases in the North Sea offshore installations were not detected by gas detection methods. To improve safety, more and more detector placement is being performed by experts using computer modeling. This computer-aided detector placement or “mapping” is the process of determining where detectors are to be placed for optimal response - from Petro-Online.

 

Conversions for Gas Detection

Useful Conversions for Gas detection - These are very handy - from Interscan Corporation.

 

Gas Detection Sensor Selection Guide

The Selection and Use of Flammable Gas Detectors - This guidance has been produced by the UK Health and Safety Executive. It provides advice and information on the selection, installation, use and maintenance of industrial flammable gas detectors.

Sensor Selection Guide - Each of the following sensor, electrochemical, catalytic bead, solid state, infrared and photoionization detectors must meet certain criteria to be practical for use in area air quality and safety applications - from International Sensor Technology.

Selecting and Placing Gas Detectors for Maximum Application Protection - Dave Opheim - Many industrial processes involve dangerous gases and vapors: flammable, toxic, or both. With the different sensing technologies available, and the wide range of industrial applications that exist, selecting the best sensor and locating them properly for the job at hand can be a challenge - from Detector Electronics Corporation.

The Detection of Hazardous Gases - The detection of hazardous gases has always been a complex subject and makes choosing an appropriate gas monitoring instrument a difficult task. This chapter provides A simple guide to the various sensor technologies available and Terms Definitions and Abbreviations - from International Sensor Technology.

 

Standards for Gas Detector Location

Location of Fixed Gas Detectors and Relevant Standards - There are no specific standards governing gas detector location (unlike fire detection systems); there are however general guidance documents. Two examples which give information on locating detectors and also selection of sensor technologies are: BS EN 50073:1999: Guide for selection, installation, use and maintenance of apparatus for the detection and measurement of combustible gases or oxygen and IEC60079-29-2 Ed1.0: Explosive atmospheres - Part 29-2: Gas detectors - Selection, installation, use and maintenance of detectors for flammable gases and oxygen – from Crowcon.

Gas Detectors - Selection, Installation, Use and Maintenance of Detectors for Flammable Gases and Oxygen - ustralian/New Zealand Standard™ Explosive atmospheres Part 29.2 - This standard has been specifically written to cover all the functions necessary to go from the need for gas detection all the way through ongoing maintenance of a successful gas detection operation.

Why my Gas Detector should be Performance Test Approved - Includes a summary of the relevant European EN standards which relate to gas detectors - from ShawCity.

Indian Standard Explosive Atmospheres Part 29 Gas Detectors Section 2 Selection, Installation, Use and Maintenance of Detectors for Flammable Gases and Oxygen - Indian Standard (Part 29/Sec 2) which is identical with IEC 60079-29-2 : 2007 ‘Explosive Atmospheres - From law.resource.org.

 

Managing Hazardous Areas Effectively by using Gas Monitors

How to Manage Hazardous Areas Effectively by using Gas Monitors - Electrical equipment installed in hazardous areas, necessarily has to conform to the area classification for that area. However, frequently, practical problems arise, where the specified equipment may not be easily available. For example, an area classified as Zone 1 under the IEC system, theoretically can accept only Zone 1 equipment. However sometimes, especially in case of specialized equipment, Zone 1 certified equipment of that type may not be available. In such cases what could be done? This paper presents the background of such situations, possible solutions and current international practices regarding this issue - from Abhisam Software.

Other useful Links

Gas Detection | Infra Red Gas Detection Technical Overview Notes |