• Intrinsic Safety, Barriers and Isolators
• HA Classification
• IEC

Electrical Equipment for Hazardous Areas - Classification, Design and Standards

Hazardous Areas Technical Guide - This excellent 90 page technical guide from Weidmuller is a large pdf download at 5 Megs, however it is worth the wait!

Intrinsic Safety, Barriers and Isolators - A full page of great links.

A Common Regulatory Framework for Equipment Used in Environments with an Explosive Atmosphere - This is a publication that helps address the hazards in environments with a high risk of explosion such as mines, refineries, chemical plants and mills. The booklet can be used by countries that lack regulation in this sector as a blueprint for their legislation, and also for aligning existing national regulations with internationally harmonized best practice.

Basics of Explosion Protection - from Stahl. 

Electrical Apparatus and Hazardous Areas - Covers Hazardous Areas, Groups, Zones, Temperature Classes, Types of Protection, Equipment Protection Levels, Standards and ATEX - from Hexagon Technology.

Hazardous Area Classification and Control of Ignition Sources - This Technical Measures Document refers to the classification of plant into hazardous areas, and the systematic identification and control of ignition sources - from the UKHSE.

Electrical Information - Including Cenelec and IEC hazardous Area Information, North American Hazardous locations, IP code information and Abbreviations, Acronyms and Definitions - From Hawke International.

Hazardous Areas Technical Guide - This publication provides a brief overview of the essential aspects of explosion protection. Ultimately, safety in a potentially explosive atmosphere is a team effort. Manufacturers have a responsibility to ensure only safe equipment is placed on the market. Installers must follow the instructions provided and use the equipment only for its intended purpose. Finally, the user has a duty to inspect and maintain the equipment in a safe working order - from Warom.

Hazardous Area Classifications and Protections - The intent of this document is to provide a broad overview of hazardous area classifications and the types of protection techniques involved - from Emerson Process Management.

Hazardous Area Installations - How to make 92% of sites safer without increasing the costs of compliance - From Abhisam Software.

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.

Minimum Ignition Energy (MIE) - In the following table MIE is quoted for flammable substances mixed with air. A reference is provided to indicate the source of the data. MIE values are provided for guidance only. Please check references for specific measurement conditions - from Explosion Solutions.

The following papers and presentations are from the IDC Technologies "Hazardous Areas: Classifications and Equipment Conference 2007", these papers are recommended reading.

Electrical Equipment in Hazardous Areas - Field Inspections - Bill Rankin - This paper focuses on the problems which are directly related to the inspection process. It has been written from the perspective of the Ex inspection team who usually have no control over the design and installation process. It is acknowledged that the competency of the design and installation personnel will affect the quality of the installation that is to be inspected. The failure of Ex inspection campaigns can be attributed to four main areas:

- Poor planning of the Ex inspection activities
- Lack of competence of the Ex inspectors
- Lack of clarity of the inspectors’ roles
- Lack of clarity of the inspection scope

Ex Inspections—Potential Pitfalls - Alan Wallace- Inlec Engineering - Many, if not most, Ex inspection campaigns are grossly inefficient, and their
effectiveness is often questionable. This presentation discusses the four main reasons why Ex inspection campaigns fail to meet the client's expectations. It also offers recommendations to improve the quality and efficiency of Ex inspections.

The Application of Intrinsic Safety to Fieldbus Systems - Chris Towle Chairman: MTL Instruments Ltd - This excellent paper covers the technical aspects of FISCO, FNICO, Exe and Exi combination, Maintenance and Inspection along with Intrinsically Safe Ethernet.

Myths and Actual Practice with Industrial Data Communications and Hazardous Areas - Steve Mackay - IDC Technologies - This presentation covers Practical examination of data communications systems in hazardous areas for Ethernet, Foundation Fieldbus, Profibus or RS-485 along with Practical guidelines for best practice in designing your next industrial data communications system in a hazardous area.

The Current State of the IEC Intrinsically Safe Standards - Chris Towle - Chairman: MTL Instruments Ltd - A candid discussion on the IEC IS standards which includes IEC Organisation, Intrinsic Safety Standards, An Analysis of the Change from ‘nL’ to ‘ic’ and advice to the First-time Designer.

Changes to Certification and its Impact on Manufacturers - Des McDonell CSE-Ex Pty Ltd - This presentation covers product certification in Australia.

Gases and Vapours - Gases and Vapours (and Mists) mix more or less homogeneously with air and form flammable mixtures relatively quickly. While this is obvious for gases, vapours can travel very quickly and form flammable or explosive mixture with air in a very short time frame - from EPEE Consulting.

Flammable / Combustible Liquids - While the dangers of flammable liquids are well known, combustible liquids can be as dangerous under certain conditions. The vapour space in storage tanks is a Zone 0 are even for combustible liquids. Should the ambient temperature approach the flash point of combustible liquid within 6 deg C, it has to be treated as if it were a flammable liquid - from EPEE Consulting.

The following papers and presentations are from the IDC Technologies "Hazardous Areas: Classifications and Equipment Conference 2009", these papers are recommended reading.

It’s Not Rocket Science Unless You Do It Wrong - Dave Adams - Technical Advisor - Hazardous Locations Equipment: Canadian Standards Association International - The certification of hazardous locations electrical equipment is changing, and will continue to change, for some time. There has never been a more confusing time for manufacturers, end-users, and certification agencies alike. This paper does not really have a point, or maybe it has several. While it provides answers, it will also raise new questions. It is really just a strung-together collection of miscellaneous observations, ramblings, and rants, garnered from 18 years in the business of certifying hazardous locations equipment.

Proper Grounding of Instrument and Control Systems in Hazardous Locations - Joe Zullo - Regional Sales Manager: MTL Americas - Grounding is defined as electrical equipment connected directly to mother earth, or to some conducting body that serves in place of the earth, such as the steel frame of a plant and its earth mat or the hull of a ship or oil drilling platform. Proper grounding is an essential component for safely and reliably operating electrical systems. Improper grounding methodology has the potential to bring disastrous results from both an operational as well as a safety standpoint. There are many different categories and types of grounding principles. This paper’s primary focus is to demonstrate proper grounding techniques for low voltage Instrument and Control Systems (IACS) that have been proven safe and reliable when employed in process control facilities.

The New Dimension of Intrinsic Safety - Rick Ogrodzinski - Project Leader - Global Projects Team, Process Automation Division: Pepperl + Fuchs, Inc - intrinsic safety type of protection is currently achieved by limiting the available power. This limitation of power - usually to less than 2 W - provides intrinsic safety (Ex i) and is therefore mainly employed in the area of control and instrumentation in the power supply to actuators and sensors with low connected load. A significantly higher direct power with the simultaneous safeguarding of all the positive characteristics of intrinsic safety offers the user a new and essentially wider scope of application. These aims are achieved through DART technology (DART: Dynamic Arc Recognition and Termination). DART is a means of instantaneous tripping, which dynamically detects an undesired condition or a fault in the electrical system precisely as it occurs and instigates an immediate transition to a safe condition before any safety-critical parameters are exceeded. DART is based on the detection of fault conditions and their characteristic rate of rise of current.

The following papers and presentations are from the IDC Technologies "Hazardous Areas Conference 2015", these papers are recommended reading.

Hazardous Area Classification of Large Scale Plants - Paul Spresser - The hazardous area classification of a large scale plants can be problematical. A preference to use the generalised method of classification exists and its use is easily substantiated, for most aspects of these plants. However, unless some clear cut guidelines are established and allowance is made for a certain level of exceptions to the main adopted methodology, impractical solutions can result. Room must be left for use of the Source of Release by example and calculation methods for a practical classification solution - from EPEE consulting and IDC Technologies.

Explosive Hazardous Areas - In the Mining Environment - Aaron Drew - This paper discusses the effects on mine design, operation and maintenance as a result of the inclusion/use of chemicals that produce explosive atmospheres. A brief discussion in relation to the acceptance of EEHA principles within the mining community - the age old how can it be hazardous when you can eat it argument. Finally, mines are interesting in as much as they may have both dust and gaseous hazardous areas, what is the outcome when the hazardous zones overlap and a piece of equipment must be certified to both dust and gaseous requirements? Is such equipment readily available in the market? - from Primero Group and IDC Technologies.

Risk Based Prioritisation of Ex Equipment Non-Compliances - Alan Wallace - In most facilities, electrical equipment in hazardous areas must be installed in accordance with AS/NZS60079.14. Due to decay, damage, incorrect original installation, or maintenance, electrical installations in hazardous area may not be fully compliant with the installation standard. Many OpCos spend hundreds of thousands of dollars conducting periodic Ex inspection campaigns, in accordance with AS/NZS60079.17. It is usually not possible to rectify all of these Ex non-compliances immediately. This is especially true when there are many Ex non-compliances. The non-compliances are usually prioritised for rectification. However, in most cases there is no structured and justifiable basis for the prioritisation applied. This paper discusses a qualitative risk based approach to prioritisation to ensure that the Ex non-compliances creating the highest risk are addressed first. The methodology achieves a balance between being simple to apply vs. considering all of the factors that contribute to the risk - from Inlec Engineering Australasia.

Training Competencies for Electrical Equipment in Hazardous Areas - Paul Egan - Within industry, there is much confusion, as whether it is a requirement to have nationally accredited competencies for any electrical work carried out with Electrical Equipment in Hazardous Areas (EEHA). The legislation in Western Australia calls up the Australian / New Zealand Standard 60079 series. AS/NZS Standard 60079-14 requires, anyone carrying out work in the areas of design, classification, installation, inspections and maintenance, be competent to the requirements of AS/NZS 4761:2008 Even though these standards clearly require certain competences to be able to carry out works in hazardous areas, there are many organisations that do not understand or don’t care to have their personnel correctly trained to these standards. It is also a requirement to have awareness training for anyone (non electrical) who is working in the hazardous area. There is also the issue of just obtaining the minimum required competencies, as this is often not enough. Further mentoring and milestone achievements are often required before a person can truly be deemed competent to carry out work in these areas. This presentation highlights the requirements for all training required and what training needs to be undertaken, to demonstrate competency in EEHA design, classification, installation, inspection and maintenance.

Death by Standards - S. Srinivas Shastri - Technology has advanced significantly over the past several decades, and this has resulted in not only better materials of construction but also in tailor made instrumentation and tight process control. As accidents have occurred in the past (Piper Alpha, Bhopal, Flixborough, and other unfortunate events) there is a greater understanding of process systems and materials. All these advances have led to documenting best industry practice in the form of standards, codes and practices. Legislation has been implemented that often draws upon these standards, however, there application of the standards is not prescriptive. The interpretation and the application of standards is the role of the practicing engineer and she/he should draw upon wisdom in ensuring compliance and most critically safety of the operation. This paper has very few references as it is an ‘applied paper’, however it does draw heavily from the usual normative hazardous area classification standards relevant to Australia - AS/NZS 60079.10.1 and API RP 505 specifically. In the context of this paper these standards are those editions that were current as of 2014. This paper discusses two classification examples from a recent large LNG project.

Area Classification and Major Hazards - Lars Rogstadkjernet - Hazardous area classification and major hazards risk assessments have a common objective: to assure a plants operability and safety by preventing ignition. Yet, the two tasks are often carried out without much consideration of the other. Hazardous area classification is prescriptive and oriented toward high frequency events whereas risk analysis is usually performance oriented and focus on rare events. Legislative requirements for major hazards typically refer to rare events: those occurring every 10 000 or 100 000 years, with the requirement being that unacceptable events cannot occur more frequent than this. Consequently, the scenarios being of concern to the risk assessor can be much different to those normally thought of for zoning purposes even if they are somehow dealing with the same problem: preventing ignition. Ignition is a major factor in a risk analysis and a potent ignition source outside a classified area may be of crucial importance. Similarly there may be areas where classification is mandated but of lesser importance in the eyes of a risk assessor. A key point for this paper is ignition hazard beyond the boundaries of area classification. Case examples will be used to illustrate how ignition from non EX areas impact on risk as well as well as examples of where EX proofing is less critical - at least in the eyes of a risk assessor.

A Case Study: Hazardous Area Considerations for Diesel Storage in a Hot Climate - Daniel Bianchini, Justin Van Staden and Harrison Cox - Hazardous areas are most often associated with the storage and handling of flammable liquids. However, in certain circumstances hazardous areas can occur around combustible fuel installations. This paper explores a specific case study involving the above ground storage of diesel in a hot climate (Pilbara, WA) and investigates scenarios to inform the understanding as to when hazardous areas might occur. Issues reviewed include the relationship between ambient conditions and the temperature of the fuel being handled, spill scenarios, and the potential formation of sprays and mists.

Hazardous Area Classification: The Dangers of Using Standards for Determination of Hazard Zones - Kehinde Shaba, Colin Hickey - There are many benefits to using standards to determine the hazard radius in hazardous area classification applications. By codifying existing knowledge they ensure rapid and timely delivery of required results. However, they suffer from a number of limitations - chief of which is a lack of specificity. This paper discusses the pitfalls/challenges of using standards for establishing hazard radii and then discusses how they can be addressed by the use of detailed consequence modelling. A case study comparison of the two approaches is also outlined as well as the benefits of using a more targeted approach.

Machine Safety in Hazardous Areas - Ross De Rango - The principal interest of this paper is zoning. Other considerations of course need to be taken into account to ensure that equipment installed is safe for the location, but it is zoning that has the most impact in the context of design choices for machine safety systems in hazardous areas.

Fire and Explosion Protection of Electrical Installations with New Advanced Suppression Systems - Andrew Kim - Senior Research Officer - Fire Research Program, Institute for Research in Construction - National Research Council of Canada The National Research Council of Canada (NRC) has carried out projects to evaluate the fire and explosion protection effectiveness of new technologies technologies which will be examined and discussed. There is a potential for a very large fire or explosion when using electrical equipment in areas where flammable gases could accumulate or in room containing power transformers. Recently, several new fire suppression technologies have been developed to provide protection in an environment with an explosive atmosphere or to provide suppression of a large fire involving electrical equipment, such as power transformers. In one project, the explosion suppression effectiveness of hybrid gas generators in providing safety to occupants in a compartment against a deflagration type explosion was evaluated. Hybrid gas generator systems combine gas generator technology with a liquid fire suppression agent. In another project, the effectiveness of a newly developed compressed-air-foam (CAF) system was evaluated to provide fire protection in power transformers. Thanks to the National Research Council Canada.

Comprehensive Global guide to Hazardous Locations - And boy is this comprehensive! It is an excellent technical resource from Cooper Crouse Hinds which includes virtually everything including: Basics of Explosion Protection, Area Classification, Methods of Explosion Protection, Equipment Selection, Installation & Wiring Practice.

Ex poster (inc ATEX) - thanks to Endress + Hauser.

Flammable Risk - from Crowcon.

Hazardous Area Classification/ Flameproofing - From the UK Health and Safety Executive.

Hazardous Area Reference Chart - From Crouse-Hinds.

Extronics Wall Chart - Some Useful Ex Information here.

MTL Luton UK Technical Information - You will have to register to get access- it is quick, easy and worth it!

Flammable Facts Poster - This poster from MTL gives a quick look at the most important facts associated with Electrical Equipment in Hazardous Areas.

A Guide to Risk Based Assessments of In-situ Large Ex 'e' and Ex 'N' Machines - Whilst not free this guide provides a practical method to undertake a comparative evaluation of the risk of incendive discharges occurring in existing large Ex 'e' and Ex 'N' high voltage machines in potentially explosive atmospheres.

How Can You Manufacture Explosion-Proof Equipment and Systems to World-Class Safety Requirements? - Depending upon the Zone of usage, electrical, electronic and mechancial equipment intended for use in potentially hazardous environments must be independently evaluated for their impact on overall safety. The European Union’s ATEX Directive and the IECEx Certified Product Scheme are two assessment routes used for the safety of equipment used in such environments. This white paper provides an overview of these two routes and provides answers to frequently asked questions. You will have to register to download this paper from TÜV SÜD. 

IECEx

The objective of the IECEx Scheme is to facilitate international trade in electrical equipment intended for use in explosive atmospheres (Ex equipment). The IECEx Scheme provides the means for manufacturers of Ex equipment to obtain certificates of conformity that will be accepted at national level in all participating countries.

IECEx Standards - The IECEx Scheme is based on the use of specific international IEC Standards for type of protection of Ex equipment.

The ExTR Database - This database provides an official listing of IECEx Ex Test Reports issued in accordance with the scheme rules, IECEx 02.

The IECEx Scheme - Description from the National Electrical Manufacturers Association.

Explosive Atmospheres - A useful bulletin from IECex.

Intrinsic Safety, Barriers and Isolators

Most IS Instruments achieve a T4 (135 deg C) which satisfies all industrial gases except Carbon Disulphide.

Because standard Instrument Cables can be used, no conduit and bulky enclosures are required the concept is the most cost effective. 

One of the largest advantages of IS is that the systems can be worked on live without a hotwork permit, however test equipment must also be IS certified. 

There are a  proportion of engineers who select  Exd (Flameproof) or Exn (Non Incendive) equipment because they see IS as being too hard to design, install and maintain, however this is a false premise as concept is the most effective method of ensuring electrical safety in the hazardous area. Actually the correct installation and ongoing maintenance of the alternative concepts (Exd, Exn, Exe etc) require more care and maintenance over the life of a facility.

The Intrinsically Safe Equipment Certificate is a very important document in that must be utilised in all phases of the facility life, hence it should be kept in a readily available Ex Equipment Dossier. It has details of design and installation requirements such as cable parameters and other specific provisions for the equipment. Each piece of IS equipment carries a certification label which designates the Ex category, Gas Group and Temperature Rating. 

Exd , Exn or other certified equipment must not be used in a IS circuit! There are some devices that are designated "simple devices" for example a switch, these do not require certificates.

A very important issue in working with Ex is Personnel Competency in the Design, Installation and Maintenance of Electrical Equipment in Hazardous Areas. There are many competency based courses available around the world and it is Essential that anyone involved in these areas are assessed and accredited to work on any Ex system. This competency should be reassessed every three years at a minimum.

Intrinsic Safety - The Fundamentals

Intrinsic Safety in a Nutshell - David Hohenstein - Intrinsic safety is the safest, least expensive, and easiest to install method of protection available. These safety systems offer significant labour savings over traditional protection methods because there are no heavy conduits or bolted enclosures. Material costs are less because a standard enclosure is the only major expense for mounting the barriers. So, how does it work? - from Pepperl and Fuchs.

Intrinsic Safety Basics - Paul S. Babiarz - Making instruments intrinsically safe need not seem like a nightmare. Here, the basics of intrinsic safety circuit design are discussed - from Omega.

Intrinsic Safety Basic Principles - A quick guide from GM International.

Intrinsically Safe Design

AN9003 A User's Guide to Intrinsic Safety - This guide from MTL  is a really excellent reference.

Engineers Guide - Process Automation Interface Technology - This Engineer's Guide is much more than just a catalogue of data sheets and specifications: it also includes a technology section with information about the principles behind field signals, explosion protection and functional safety. Appropriate application examples illustrate the main features - Go to page 37 for the Intrinsic Safety Section - This an excellent resource from Pepperl and Fuchs.

Uwhat? - Understanding I.S. Terminology - Covers Associated Apparatus, Output Parameters, Safety Description, Reactance Parameters, Field Equipment, Alternative Notations and Other Parameters - from RTK Instruments.

Protecting the I.S. System from Outside Influences - Covers Precautions, Capacitance, Surge Protection, Mechanical Protection and Cable Installations - from RTK Instruments.

Intrinsically Safe or Explosion proof - Understanding the Technology - The phrase “Intrinsically Safe” is often used generically to describe products destined for hazardous (explosive) areas. This paper explores the term “Intrinsically Safe”, provides an overview of what is required to certify a product and compares Intrinsic Safety against Explosion Protection concepts - from CorDEX Instruments.

Assembling an Intrinsically Safe System - Covers the Barrier System, Simple and Non-Simple Apparatus, Incomplete Parameters, System Category, Variations, Cables along with a simple logic table for the selection of the correct barrier or Isolator - from RTK Instruments.

Intrinsic Safety in Hydrogen/Oxygen Mixtures - Occasionally it is necessary to make measurements in hydrogen/oxygen mixtures. The increased use of fuel cells and the use of hydrogen as a vehicle fuel have increased the frequency with which this requirement occurs. The requirement occurs usually within process vessels since when the mixture is released the problem becomes a mixture of hydrogen/oxygen /air which is a slightly different problem. Conventional intrinsically safe equipment certified to the IEC standard is considered to be adequately safe under normal atmospheric conditions. The ATEX guidelines on the 94/9/EC directive state ‘A product within a potentially explosive mixture without the presence of air is not in the scope of the directive’. It follows therefore that that a safety analysis of an electrical installation in a hydrogen/oxygen mixture must be based on a risk analysis using the best available information. The conventional IS certification ensures a satisfactory level of construction but additional consideration must be given to the levels of voltage, current and power used. This note proposes an approach, which the author considers, achieves an acceptable level of safety.  

How to Calculate an Intrinsically Safe Loop Approval - Gary Friend - We all know what can happen if the correct techniques are not used when interfacing into the hazardous area. Using intrinsic safety (Ex i based on IEC/SANS 60079-11; IEC/SANS 60079-25), the energy in the hazardous area is limited to below the ignition energy of the gas present, thereby preventing explosions - from South African Instrument & Control.

Associated Apparatus

Associated Apparatus is the equipment interfaces between field and control room equipment. These are usually Zener Barriers or Isolators which protect the Hazardous Area circuits by limiting the voltage and current in normal and under fault conditions. Zener Barriers or Isolators used in Intrinsically Safe circuits must be designed and certified as Associated Apparatus suitable for connection to the selected intrinsically safe or simple apparatus in hazardous Area. The Associated Apparatus is designed to achieve the maximum allowable safety parameters of the circuits connected the Hazardous Area terminals of the barriers. Associated Apparatus has slightly different identification than the field equipment because it is installed in the safe area. An example of this is [EExia]IIC , note the brackets, these highlight that the equipment must be mounted in the safe area.  

Earthing and Bonding in Hazardous Areas

A Definitive Guide to Earthing and Bonding in Hazardous Areas. LC Towle - This document details what has proved to be acceptable practice for earthing and bonding of electrical apparatus used in hazardous areas. The subject is not complex, but partially because it is relevant to more than one area of electrical expertise a systematic approach to the subject is desirable. There are numerous codes of practice which specify how earthing and bonding should be carried out, but the fundamental requirements are independent of the geographic location of the installation and hence there should be no significant difference in requirements. This document predominantly describes what is acceptable prac tice in the United Kingdom and Europe. If a national code of practice exists and differs fundamentally from this document then it should be questioned. It may be considered expedient to comply with such a code but it is important to be assured that doing so results in a safe installation. Some parts of this note state what are well known basic principles to practising electrical and instrument engineers. They are restated primarily for the sake of completeness, and ease of reference - from MTL.

The Earthing of Zener Barrier Installations - Details Barrier Earth, Code of Practice, Practical Earth Connection, Making the Earth Connection, Cable Installations and Special Cases - from RTK Instruments.
Engineers Guide - Process Automation Interface Technology - This Engineer's Guide is much more than just a catalogue of data sheets and specifications: it also includes a technology section with information about the principles behind field signals, explosion protection and functional safety. Appropriate application examples illustrate the main features - Go to page 63 for the Earthing Section - from Pepperl and Fuchs.

Gases Classification Relative to Ignition Temperature

Subdivision of Gases and their Classification Relative to Ignition Temperature - These tables list gases which are subdivided by hazardous area classification according to ignition temperature and temperature class from GM International.

Hazardous Area Verification Dossier

Hazardous Area Verification Dossier - Australian Standards AS/NZS 2381.1:2005 and AS/NZS 61241.1.2:2000 state that a ‘Hazardous Area Verification Dossier’ shall be prepared for all electrical installations located in a defined hazardous area. AS/NZS 2381.1:2005 and AS/NZS 61241.1.2:2000, both state in part that, ‘It is necessary to ensure that any installation complies with the appropriate documents, this standard and any other requirements specific to the plant on which the installation takes place.’ A verification dossier shall be prepared for every hazardous area installation and kept on the premises. The dossier should contain the information detailed in the relevant Australian Standard for the type of protection concerned. This Installation Advice gives details on necessary content of the dossier - from Clean Energy Australia.

Intrinsically Safe Cables

Low voltage and current in intrinsically safe circuits allow the use of ordinary instrumentation cables provided that capacitance and inductance are taken into account in assessing the safety of the system. Cable parameters seldom are rarely a problem and long distances can be easily achieved. Generally Intrinsically Safe cable calculations are completed at the design stage, however really a good method is to review all the IS equipment certificates and determine the most onerous case and calculate the distance for that particular circuit plus devices. The Minimum Ignition curves along with the Equipment Maximum Cable Parameters and the Actual Cable Parameters are used in the calculation. Thus all the other circuits must then comply since they would give longer distances. Of course this must be documented in the IS Equipment section in the Hazardous Area Verification Dossier.

Cables for I.S. Installations - Covers Cable Parameters, Individual /Multicore Cables, Sheath Cover, Screens and Sheaths along with the need for Cable Segregation - from RTK Instruments.

Cable Parameters and All That - The intrinsically safe [IS] system standard [IEC60079-25] discusses in detail how to draw up the system documentation and in particular how to calculate the permitted cable parameters. Unfortunately the standard has to take into account all the possible variations and hence the process looks quite complicated. In the majority of applications the simple precaution of using a single source of power with no significant capacitance or inductance across its output terminals [Ci &Li] and field devices with only small input capacitance and inductance [Ci & Li] removes any problems - from MTL.

Engineers Guide - Process Automation Interface Technology - This Engineer's Guide is much more than just a catalogue of data sheets and specifications: it also includes a technology section with information about the principles behind field signals, explosion protection and functional safety. Appropriate application examples illustrate the main features - Go to page 62 for the Intrinsic Safety Cables Section - from Pepperl and Fuchs.

Junction Boxes

Thoughts on the Design of Intrinsically Safe Junction Boxes - Junction boxes are ‘simple apparatus’ when used in intrinsically safe circuits, and given a little thought they can make life simpler for the installation and maintenance engineer - from MTL.

Minimum Ignition Curves

Minimum Ignition Curves - The following graphs answer the question: What is a dangerous amount of electrical energy? These graphs are for circuits containing aluminium, cadmium, magnesium or zinc-substances that produce a high temperature incendiary spark. It is important to keep in mind that these curves reflect the worst case scenario. When designing intrinsically safe electronic equipment today, most manufacturers start by specifying the equipment for the worst possible case. The graphs chosen are those that are used most often by designers and manufacturers of electrical apparatus from GM International.

Simple Apparatus / Devices

These are passive components (switches, resistive sensors, potentiometers), simple semiconductor (LEDs, phototransistors) and simple generating devices (thermocouples, photocells) are regarded as Simple Apparatus if they do not generate or store more than: 1,5 V, 100 mA, 25 mW. Simple Apparatus can be used in Hazardous Area without certification; they have to be assessed for the temperature classification on the basis of the matched output power of the interface device.

Simple Apparatus - or not so simple? - Describes the concept of Simple Apparatus, Increased Scope, Distributed Inductance, Added Complications, Inviolate Assemblies, Care with Cables, Temperature Category and Limitations of Use - from RTK Instruments.

Zener Barriers and Isolation Devices

While a zener diode barrier is normally the most cost-effective solution, the intrinsic safety isolator using galvanic isolation is normally the superior, long-term performance solution. This is because galvanic isolation and the additional electronics used within intrinsic safety isolators provide better noise immunity, signal conversion options, application-specific designs, no intrinsic safety ground connection/maintenance requirements, signal enhancement, logic control features, and fewer impedance concerns. The term galvanic isolation is often linked to and identified with an intrinsic safety isolator. This is because intrinsic safety isolators use galvanic isolation components such as transformers, relays, and capacitors. Both the zener barrier and IS isolator are used to provide energy limitation to circuits/components mounted in hazardous ‘classified’ locations. Since these hazardous locations are ignition capable, it is important to provide a reliable means of limiting energy that can be transmitted so an explosion hazard is not created during normal or fault operation of the circuit. So, the decision to use an intrinsic safety isolator (galvanic isolation) or zener barrier really comes down to the application - from Pepperl and Fuchs.

The following is from the excellent publication South African Instrument and Control; A Zener barrier is a simple device where the voltage is limited by a Zener diode and the current by a resistor. A fuse is present to protect the Zener diode as shown in Figure 1. The key to safety is the intrinsically safe earth. Without it, there is no protection. If the input voltage increases above Zener diode voltage, the Zener conducts and the fuse blows, after which the Zener barrier needs to be replaced. In addition, the barrier has a volt drop across it under normal operating conditions, so careful calculation must be done to ensure that there is sufficient voltage at the field device. [Note: using Zener barriers without an IS earth is not safe.]

Figure 1.

Galvanic isolator

A galvanic isolator is an active device that energy limits without the dependence on the IS earth for safety as shown in Figure 2. It also has the advantage of supplying higher voltage at the hazardous area terminals and allowing longer cable lengths. Isolators have local LED indication and most 4-20 mA isolators transfer Hart communications through the optical isolation.

Figure 2.

Engineers Guide - Process Automation Interface Technology - This Engineer's Guide is much more than just a catalogue of data sheets and specifications: it also includes a technology section with information about the principles behind field signals, explosion protection and functional safety. Appropriate application examples illustrate the main features - Go to page 57 for the Intrinsic Safety Zener Barriers and Isolator Section - from Pepperl and Fuchs.

Zener Barriers or Isolation Interfaces? - Covers Types of Interface, Earthing, Insulation Requirements, Discharge Path, Zone 0 Installations, Supply Voltage Tolerance, Power Requirements, Dissipation, Application Flexibility, Accuracy, Response, Reliability, Security along with a comparison table - from RTK Instruments.

Intrinsic Safety Applications

Load Cell Intrinsically Safe Installation Application Note - When the weight indicator or digitiser is not Intrinsically Safe it may not be placed in a Hazardous Area. However, strain gauge load cells are inherently passive devices and ‘safe’. (Although long cables may exceed capacitive and inductive limitations ~ a barrier to load cell cable length of 100m is usually no problem; other limitations not withstanding). So load cells may be placed in the Hazardous Area so long as the power delivered to them is strictly limited under any fault condition. Shunt Diode Safety Barriers are used to limit the power to safe levels, but their use must be according to approved safety practice - from Ian Fellows Ltd

Intrinsically Safe Fire Protection Devices -The need for safety in potentially explosive atmospheres where electrical devices are used has increased substantially over the past several years. Today, applications for intrinsic safety abound in virtually every industry. The purpose of this guide is to provide general information on intrinsic safety and fire protection in hazardous areas - from System Sensor.

Intrinsically Safe Mobile Phones and Other Neat Devices - The following websites are worth a look.
ECOM Mobile Safety
i.safe Mobile
PIXAVI

Questions on Intrinsic Safety or Ex equipment? See ICEweb's Electrical Equipment in Hazardous Areas Technical Information Page.

Looking for Intrinsic safety in Fieldbus Systems? See ICEweb's Fieldbus page.

For Information on Selection, Installation and Maintenance of Electrical equipment in Hazardous Areas and other protection concepts + HA Classification see ICEweb's Electrical Equipment in Hazardous Areas Technical Information page.

The following are from the South African Flameproof Association

• Cost Comparison of Methods of Explosion Protection
• Comparison of the Techniques of Intrinsic Safety ‘ic’ and Energy Limitation ‘nL' - Some years ago [2002?] a decision in principle was made by the IEC committee TC31 to discontinue the energy limited technique from the Type’n’ standard IEC 60079-15 and transfer the responsibility for this safety technique to the intrinsic safety [IS] sub-committee. This was largely because the relevant expertise was available within the IS committee and the change coincided with some thinking on the application of categories of safety to hazardous area equipment. This decision is now feeding through the system as the ‘ic’ technique. It is embodied in the current issue of the apparatus standard [IEC 60079-11] the CDV of the system standard [IEC 60079-25] and the FISCO standard [IEC 60079- 27]. The next edition of the IEC code of practice [IEC 60079-14] contains a useful guide to the corellation between the three levels of protection and the recently introduced concept of ‘Equipment Protection Levels’ [EPLs]. The ‘nL’ concept is dealt with in one sentence “Energy-limited circuits ‘nL’ shall comply with all the requirements for intrinsically safe circuits ‘ic’” The basic principle remains unchanged, that is to create a system which is intrinsically safe in ‘normal operation’. Normal operation includes open circuiting and short-circuiting of field wiring so as to permit ‘live working’. In addition there are some construction requirements so as to ensure a reasonable level of integrity. The situation is slightly confused because the North American practice is to use ‘non-incendive’ apparatus in Division 2, which is almost the same as ‘nL’ apparatus but not quite. The major difference is that ‘non-incendive’ apparatus uses a factor of safety of 1,1 on the usual IEC ignition curves whereas the ‘nL’ standard and the ‘ic’ requirement is a unity factor of safety. This means that ‘ic’ and ‘nL’ apparatus may not meet the requirements of ‘non-incendive’ apparatus although in the majority of cases it does. The use of cadmium discs and the most easily ignited mixture of gases within the test apparatus are considered to ensure an adequate factor of safety for Zone 2 purposes. This change in safety factor means that the available power in ‘ic’ circuits is greater than that in other IS circuits. It is important to recognise that the significant effect of the change to ‘ic’ is that the application of this equipment is clarified but there is no intention to modify the fundamental principle. The remainder of this note highlights the areas where this clarification is effective. In the past the absence of positive guidance enabled individuals to make decisions, which they considered adequately safe. Some more expert practitioners will regret the loss of this flexibility. Possibly the ‘non-incendive ‘technique will live on for some time because of this factor.

Shunt-Diode Safety Barriers and Galvanic Isolators - a Critical Comparison - The discussion on the relative merits of galvanic isolators and shunt diode safety barriers has been carried on for many years. The majority of other articles on this subject have aimed to prove the superiority of one technique over the other. This paper brings together the illustrations which have accumulated over a considerable time in response to various questions raised at presentations. It attempts to make balanced arguments so that the reader can decide the most suitable technique for a particular application. It ends with a score sheet which might be found useful if a decision is not completely self-revealing - from MTL.

Intrinsic Safety - The Appropriate Technique for Zone 2 - L C Towle - Concern for safety, economy and ecology has led to progressively more effective steps being taken to reduce the possibility of significant leakage of flammable substances on all types of petrochemical plant. As a consequence, the major part of most potentially hazardous plants are now designated Zone 2. In practice, if large areas of a plant are designated as Zone 0 or Zone 1 then inspection authorities are likely to ask if all reasonable measures have been taken to minimise leaks. This tendency to classify the major part of the plant as Zone 2 naturally suggests that the precautions considered necessary for the use of electrical equipment can be relaxed, and the possibility of using type ‘N’ equipment naturally follows. This document explains why, in the particular case of process control instrumentation, this apparently logical progression is not a sound idea and why intrinsic safety is still the preferred technique - from MTL.

Intrinsic Safety in Fieldbus Systems

FISCO Intrinsically Safe Fieldbus Systems - This application note is a practical guide to the selection, installation and maintenance of equipment complying with the Fieldbus Intrinsically Safe Concept (FISCO). The document begins with a discussion of the origins of FISCO and an introduction to the main elements that should be considered when assembling FISCO systems. Later sections then develop each subject in more detail, with the intention of providing clear guidance to new and experienced fieldbus users - from MTL.

Surge Protection for Intrinsically Safe Systems - This publication discusses the nature of the threat to intrinsically safe instrumentation in hazardous areas from voltage surges induced by lightning or other causes. The practical application of surge protection devices (SPDs) is also considered taking into account the certification/approvals requirements.

Intrinsically Safe Fieldbus In Hazardous Areas  - Armin Beck - Decision Guidance for Intrinsically Safe Fieldbus Solutions - Currently different solutions are available for intrinsically safe fieldbus like Entity, FISCO or High-Power Trunk and recently announced redundant FISCO and DART concepts. This paper chronologically accounts the history of all intrinsically safe explosion protection concepts for fieldbus and gives an outlook on DART and the redundant FISCO concepts. The paper then goes on to compare all methods one-on-one with a practical view on their merits and drawbacks. This paper is directed at technical decision makers involved in planning fieldbus topologies for the hazardous area in search of solutions - from Pepperl & Fuchs.

DART Ushers in the Next Generation of Intrinsic Safety - In the process industries, fieldbus technologies have helped many process users to manage their assets intelligently based on the wealth of information that smart field devices can deliver. However, fieldbus in hazardous areas requires particular attention with regards to explosion protection. Here, power restrictions on equipment that limit the network device-count can make some installations cumbersome or difficult to realize. Since the advent of intrinsic safety (and later fieldbus), several concepts have addressed this problem with incremental success. Now, a new concept “Dynamic Arc Recognition and Termination (DART)” has eliminated the power problem while maintaining intrinsically safe energy levels of power supply, installation components down to the device with a new approach to energy limitation. The concept allows for considerably higher direct power, while ensuring intrinsically safe energy requirements via rapid disconnection - from Pepperl & Fuchs.

Dart - The New Dimension in Intrinsic Safety  - Udo Gerlach, Thomas Uehlken, Ulrich Johannsmeyer, Martin Junker and Andreas Hennecke - Intrinsic safety is a worldwide accepted type of ignition protection, which offers many advantages over other types of ignition protection. The dynamically acting intrinsically safe energy supply concept DART is a means of facilitating considerably higher direct power, with simultaneous intrinsically safe energy limitation through rapid disconnection. This paper explains the principle of operation of DART as well as two areas of industrial application. It also illustrates the essential technical safety aspects necessary for the demonstration of intrinsic safety and explains the impact of these on the relevant international standards. In conclusion, practical areas of application in the process industry are examined - from Pepperl & Fuchs.

The New Dimension of Intrinsic Safety - Rick Ogrodzinski -  Intrinsic safety type of protection is currently achieved by limiting the available power. This limitation of power - usually to less than 2 W - provides intrinsic safety (Ex i) and is therefore mainly employed in the area of control and instrumentation in the power supply to actuators and sensors with low connected load. A significantly higher direct power with the simultaneous safeguarding of all the positive characteristics of intrinsic safety offers the user a new and essentially wider scope of application. These aims are achieved through DART technology (DART: Dynamic Arc Recognition and Termination). DART is a means of instantaneous tripping, which dynamically detects an undesired condition or a fault in the electrical system precisely as it occurs and instigates an immediate transition to a safe condition before any safety-critical parameters are exceeded. DART is based on the detection of fault conditions and their characteristic rate of rise of current - from Pepperl & Fuchs. 

Motion Control

The following excellent information on Motion Control including Basics of Motor Control, Filtering, Adaptive Control, Positioning components, Synchronising, Loop Variations and Backlash Instability can be found at the Motion Controllers Reference Centre.

I nformation on Microcontrollers, Dedicated Boards, Pneumatic Controls, Special ICs, Cell Controllers, Timers and Counters, Board Level, Programmable Controls and Cable Carriers can be found at the Motion Controllers Reference Centre.

Fundamentals of Motion Control - In this tutorial from National Instruments you will learn the fundamentals of a motion control system including software, motion controller, drive, motor, feedback devices and I/O.

Electrical Test and Measurement Equipment

Go to Specific Subject: Electrical Installation Safety Testing using Test and Measurement Equipment | Electrical Insulation Testers | Electrical Insulation Testing | Testing of Residual Current Devices | Low Voltage Electrical Installations Safety and Measurements in Practice | Other Useful Electrical Test and Measurement Information | Electrical Low Resistance Testing | Electrical Safety | Inspection and Testing of Electrical Equipment | Self Training Manual for Electrical Measuring Equipment | Use of Electrical Test Equipment |

The following Technical Information is provided by Zedflo Australia, they are experts in Electrical Test and Measurement Equipment. 

Electrical Test and Measurement Equipment is an essential part of any Electrician's tool kit. With today's technological advances high quality electrical test and measurement tools are required. By purchasing highly specified equipment one can be assured of safety, accuracy and robustness along with user interfaces which make them more user friendly. The equipment is used to test and verify safety and operating parameters of Electrical Equipment. Typical Electrical Test and Measurement Equipment tests Insulation resistance, Continuity of protective conductors and equipotential bonding, Residual Current Devices , Line Impedance, Fault Loop Impedance, Earth Resistance, Phase Sequence, Voltage and Frequency, PE Test Terminal, Overvoltage Category, HV, Step / Contact Voltage and Earth Resistance.

Electrical Installation Safety Testing using Test and Measurement Equipment

Electrical Installation Safety Tips - This is a super electrical installation safety information resource which covers Electrical Installation Safety Testing, testing safety of electrical installations, Insulation resistance, Continuity of protective conductors and equipotential bonding, RCD testing, Line impedance, Fault loop impedance, Earth resistance, Phase sequence, voltage and frequency, PE test terminal, Overvoltage category, HV, Step / Contact Voltage and Earth Resistance, Basics of insulation measurements, Types of insulation testing, Testing safety of electrical equipment, Testing the safety of machines and switchboards, Power Quality Testing, LAN Cabling Certification, Indoor Environment Quality, Multimeter/Clamp/Voltage and Continuity Testers.

Guide to Testing and Tagging Portable Electrical Equipment and Residual Current Devices at Workplaces - As prescribed by the Occupational Safety and Health Regulations 1996 (the OSH regulations), the person having control of a workplace or access to that workplace, i.e. Employer, self-employed person, main contractor, must ensure that all portable plug-in electrical equipment and residual current devices (RCDs) at the workplace are safe and appropriately inspected, tested and maintained by a competent person. This document will assist with regulatory compliance by providing guidance on who can inspect and/or ‘test and tag’ such portable equipment and devices - from Worksafe WA.

Electrical Insulation Testers

Electrical Insulation Testers - Peter Gabrovšek - This White Paper covers Dangers for the Electrician, How Transients and Surges Occur, How High Energy breakdowns take Place, Why a Breakdown at the Origin of Installation can have More Severe Ramifications, How the Standards Deal with Overvoltages, Overvoltage Protection Categories as Defined in IEC/EN 60364, Overvoltage Categories and Electrical Installation Testers, Protective Measures in Installation Testers, Other Safety Considerations, Common Misinterpretation of the Overvoltage Protection Classes.

Electrical Insulation Testing

Guide to Modern Insulation Testing Manual - The intention of this 48 page handbook is to better acquaint the reader with the extensive problems associated with insulation measurements. The manual covers:

• The basics of insulation measurement and terms that are regulating this field. Special attention is given to terms and definitions that users of measuring equipment meet daily.
• Types of insulation testing.
• Typical problems during insulation measurement.
• Important connections for testing insulation resistance. The complete sequence is shown, from the perception of the problem, preparation and measurement, along with analysis and results.

Testing of Residual Current Devices

Testing of Residual Current Devices (RCD) - B type RCD - this White paper details the basics about RCD's, Producers of RCD's, International Reference Standards for RCD's, Testing of B type RCDs and Test Instruments.

Low Voltage Electrical Installations Safety and Measurements in Practice

Short Theory about The Safety and Measurements in Practice on Low Voltage Electrical Installations - Janez Guzelj - This white paper covers the TN System, TT System, Ensuring Safety along with Actual Practice of the Measurements on the Electrical Installation.

Measurements on Electric Installations in Theory and Practice Instruction Manual - This manual is designed for electrical engineers who deal with measurements on new or modified low-voltage electrical installations in buildings or with the maintenance of these installations. In the manual the user can find an explanation for many practical problems whilst performing measurements and directions on how to solve the problems by using the measurement instruments produced by METREL d.d.

Other Useful Electrical Test and Measurement Information

Measuring Instruments and Testers - This Technical Catalogue covers Electrical Installation Safety , High Voltage Insulation / Continuity / Earth, Appliance / Machine / Switchboard Safety, Power Quality Analysis , LAN Cabling Certification, Indoor Environment Quality, Digital Multimeters / Clamp Meters / Voltage and Continuity Testers, Variable transformers / Equipment for laboratories and Schools - from METREL.

Electrical Low Resistance Testing

A Guide to Low Resistance Testing - Understanding and Measuring Low Resistance to Ensure Electrical System Performance - The purpose of this booklet is to help the engineer, technician or operator understand:

• The rationale behind low resistance testing.
• How to make a low resistance measurement.
• How to select the proper instrument for the testing application.
• How to interpret and use the results.

Thanks to Techrentals.

Electrical Safety

Managing Electrical Risks in The Workplace - Code of Practice - This Code provides practical guidance for persons conducting a business or undertaking on managing electrical risks in the workplace. It applies to all workplaces where a person conducting a business or undertaking has management or control of electrical equipment, including electrical installations, or carries out electrical work on or near energised electrical equipment, including electrical installations - from Safework Australia.

Department of Energy Handbook on Electrical Safety - The Electrical Safety Handbook presents the Department of Energy (DOE) safety standards for DOE field offices or facilities involved in the use of electrical energy. It has been prepared to provide a uniform set of electrical safety guidance and information for DOE installations to effect a reduction or elimination of risks associated with the use of electrical energy. The objectives of this handbook are to enhance electrical safety awareness and mitigate electrical hazards to employees, the public, and the environment. It has a section on working with test instruments and equipment.

A Review of Common Electrical Safety Test Requirements - Dwayne M Davis - Four Tests are commonly used to verify electrical safety, they are Line Leakage, Insulation Resistance, Ground Bonding and Dielectric - withstand testing. This white paper details each of these tests - from associated research.

Electrical Safety Testing Reference Guide - This document from the Power Sources Manufacturers Association is a useful information source. It explains the need for and the basis for Electrical Safety Testing.

Electrical Test Equipment for Use by Electricians - This document gives guidance to electrically competent people involved in electrical testing, diagnosis and repair. Electrically competent people may include electricians, electrical contractors, test supervisors, technicians, managers or appliance repairers. It offers advice in the selection and use of test probes, leads, lamps, voltage indicating devices and measuring equipment for circuits with rated voltages not exceeding 650V - from the HSE (UK).

Inspection and Testing of Electrical Equipment

Testing Manual for Electrical Equipment - Nahed Al-Hajeri and Anantha Madhavan - The purpose of this testing manual is to provide guidelines for inspection and testing of Electrical Equipment in compliance to relevant international standards/specifications. It provides information on procedures and testing of Major Electrical equipment to be followed during testing by engineers and also furnish evidence that an electrical equipment/device is free of inherent flaws or faults. The tests on equipment/system have been broadly categorized into two categories viz. Factory Acceptance Test (FAT) and Site Acceptance Tests (SAT). These tests have been tailored to ensure design, construction and performance requirements of the equipment. This testing manual includes High Voltage Switchboards, Low Voltage Switchboards, Transformer, Diesel Generator Sets, Induction Motors, Cables, Un-interrupted Power Supply (UPS), Ring Main Unit, Light Fittings, MOV Actuators, Isolator Switch and Earthing Systems etc. However in this Paper only highlights the high voltage cables and related test methods - from EPPM.

Self Training Manual for Electrical Measuring Equipment

Introduction to Test Equipment - This 272 page Training Module from the US Navy is an introduction to some of the more commonly used test equipment and their applications. Whilst designed for Naval use it is a very useful self training tool.

Use of Electrical Test Equipment

Use of Electrical Test Equipment - Test equipment is necessary for determining proper set-up, adjustment, operation, and maintenance of electrical systems and control panels. The following is a general procedure for use of test equipment - from US Forest Service.