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

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


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 |

EIT Latest News

Engineering Institute of Technology