Australian Ex Standards for Gas Detection in Explosive Atmospheres

Design of Equipment
AS/NZS 60079.29.1:2008: Explosive atmospheres - Gas detectors - Performance requirements of detectors for flammable gases	Specifies general requirements for construction, testing and performance, and describes the test methods that apply to portable, transportable and fixed apparatus for the detection and measurement of flammable gas or vapour concentrations with air. The apparatus, or parts thereof, are intended for use in potentially explosive atmospheres and in mines susceptible to firedamp.
Installation
AS/NZS 60079.29.2:2008: Explosive atmospheres - Gas detectors - Selection, installation, use and maintenance of detectors for flammable gases and oxygen	Specifies general requirements for construction, testing and performance, and describes the test methods that apply to portable, transportable and fixed apparatus for the detection and measurement of flammable gas or vapour concentrations with air. The apparatus, or parts thereof, are intended for use in potentially explosive atmospheres and in mines susceptible to firedamp.
Hazardous Area Classification
AS/NZS 60079.10:2009: Electrical apparatus for explosive gas atmospheres - Classification of hazardous areas (IEC 60079-10:2002 MOD)	Specifies the classification of hazardous areas where flammable gas or vapour risks may arise, in order to permit the proper selection and installation of apparatus for use in such hazardous areas.
Other
AS/NZS 60079.20:2012: Electrical apparatus for explosive gas atmospheres - Material Characteristics for Gas and Vapour Classification - Test Methods and Data - Classification of Gases and Vapours.	This part of IEC 60079 provides guidance on classification of gases and vapours. It describes a test method intended for the measurement of the maximum experimental safe gaps (MESG) for gas- or vapour-air mixtures under normal conditions of temperature1 and pressure so as to permit the selection of an appropriate group of equipment. The method does not take into account the possible effects of obstacles on the safe gaps. This standard describes also a test method intended for use in the determination of the auto-ignition temperature of a chemically pure vapour or gas in air at atmospheric pressure. The tabulated values of chemical and engineering properties of substances are provided to assist engineers in their selection of equipment to be used in hazardous areas

Australian Electrical Equipment In Hazardous Areas Standards (Gas)

Go to Specific Subject: HA Standard Application Use and Limitations | Hazardous Area  Design | Classification of Hazardous Areas | Electrical Equipment for Hazardous Areas Protection Concepts | Hazardous Area Installations Verification Dossiers | Electrical Equipment in Hazardous Areas Installation and Maintenance | Repair and Overhaul of Electrical Equipment in Hazardous Areas | Inspection of Electrical Equipment in Hazardous Areas | Limitations of Australian Hazardous Area Standards | Other Useful Standards and Handbooks | Static Electricity in Hazardous Areas | Foreign Ex Standards

This is an updated version of a paper presented at a IICA seminar 'Power & Control Equipment in Hazardous Locations', Perth, 16-17Sep 1986. It is in my opinion a very useful guideline for working within the standards associated with electrical equipment in hazardous areas. ICEweb acknowledges the assistance and review of the document by Inlec Engineering. It should be noted that these standards are amended and updated on a regular basis, whilst ICEweb endeavours to keep the information as up to date as possible users should ensure they utilise the latest editions. These can be found by searching AS/NZS standards publisher SAI Global.

 

Australian Standards for Electrical Apparatus in Hazardous Areas - Explosive Gas Areas

J A Russell IEng, FIICA

 

Introduction

This paper takes a practical approach to Australian Hazardous Area Standards taking the reader through them from conceptual design to maintenance. It does not cover dust hazards.

Australian Standards must be regarded as the PRIME Hazardous Area design guide in Australia. Some engineers are unnecessarily critical of the Standards, but these documents must be respected for what they are, namely information and advice dossiers which have been built up from design and practical experience over the years not only in Australia but from international sources (most Australian Standards have been based on the International Electrotechnical Commission [IEC] and the British Standards Institution [BSI] Standards).

Foreign Standards are not a substitute for Australian Standards. The only circumstances warranting the use of Foreign Standards is where the equipment is not available in an Australian certified form.  It should be noted that the use of foreign standards may require specific approval from an authority relevant to the particular industry.

AS/NZS3000-2007 -Electrical Installations - The Australian and New Zealand Wiring Rules is the most important Australian Standard pertaining to Electrical Installations in Hazardous Areas. Compliance with this Standard is mandatory under certain Federal and State Acts.

The Australian Standards can be of tremendous assistance to anyone involved in a Hazardous Area environment from engineers and technicians to fitters and process personnel. Admittedly they do have some limitations but which document doesn't.

In this paper some limitations of the Standards are detailed to foster awareness, however it is not intended to be derogatory to Standards Australia.

Hazardous dust atmospheres, although not part of the scope of this paper, are mentioned.

 

Australian Standards for Electrical Apparatus in Hazardous Areas - HA Standard Application Use and Limitations

 

Hazardous Area Design

Primarily the design engineering group must be in possession of the following

• An adequate Scope of Work and process description
• Process and Instrumentation diagrams (P & ID's)
• Plant layouts and elevations

If these documents are not available design should not proceed.

This base documentation is utilised in conjunction with AS/NZS60079.10 Classification of Hazardous areas - Explosive Gas Atmospheres (Replaces AS2430.1) to determine the extent and degree of the hazard. 

The following definitions are important to remember, see Table 1.

Table1

AS/NZS60079.10  EXPLOSIVE GAS ATMOSPHERES (Replaces AS2430.1) Gas areas are subdivided into zones as follow; ZONE 0 - In which an explosive atmosphere is present continuously, or is expected to be present for long periods, or for short periods which occur at high frequency. (More than 1000 hours per year) ZONE 1 - In which an explosive gas atmosphere can be expected to occur periodically or occasionally during normal operation. (More than 10 hours per year but less than 1000 hours per year) ZONE 2 - In which an explosive gas atmosphere is not expected to occur in normal operation and when it occurs is likely to be present only infrequently and for short duration. (Less than 10 hours per year)

NOTE: For the full definitions refer to the above Standard

 

Classification of Hazardous Areas

Initial classification of the Hazardous Areas should be carried out by Process or Chemical Engineers as they are more familiar with the source/quantity of release, source or ignition, flashpoint, ignition temperature and plant operation concepts.

It is recommended that any engineer, even if he has used the Standard before, reads it several times prior to attempting to classify zones.

Competency for working with electrical equipment for hazardous areas is critical and there are several providers who undertake training and assessment in this area. 

These include:

CNW Training Academy 

Moxi Skill + Learning

Courses and Assessment are based on the following standard:

AS/NZS4761 - Competency for working with electrical equipment for hazardous areas 

Part 1 - Competency Standards 

Part 2 - Guide for Training and Assessment  

MP 87:2004 : Australian/New Zealand Certification Scheme for explosion-protected electrical equipment (ANZEx Scheme) - Contains the basic rules and procedures for the management, administration and operation of the Australian/New Zealand Certification Scheme (ANZEx Scheme) for explosion-protected electrical equipment.

The " base" drawings utilised for the Hazardous Area drawings are usually the "to scale" plant layouts and elevations.

The engineer responsible for classification then classifies the plant area in accordance with the following standards. These Standards are only a guide and under no circumstances cover all plant concepts. They do however cover the most common ones. From these examples it is usually possible to deduce the Hazardous Area for an unusual portion of plant. In these circumstances it is important to document the reasons for determining a particular Hazardous Area.

Classification of Hazardous Areas - Liquids, Gases & Vapours

AS/NZS60079.10- Explosive Gas Atmospheres

AS/NZS 60079.10.1 Explosive atmospheres - Classification of Areas - Explosive gas atmospheres 

AS/NZS60079.20 - Data for flammable gases and vapours

Hazardous Area drawings should detail the source of release, gas group and temperature class and show the Hazardous Area in "cross hatching" as shown in AS/NZS60079.10.

On completion of the initial Hazardous Area drawings the responsible Engineer should pass co-ordination prints to the Electrical, Instrumentation, Mechanical and Safety Engineers. These personnel are responsible for reviewing and checking the document in relation to their own discipline.

The final "Issued for Construction" drawing should then again be reviewed and signed by the responsible Engineer of all the pertinent disciplines.

This group involvement cannot be stressed enough since if the requirements of the Standard are not met expensive remedial work may be required later in the project.

 

Electrical Equipment for Hazardous Areas Protection Concepts

On completion the Hazardous Area drawings are utilised by the Electrical/instrumentation Engineers for the system design along with AS/NZS2381.1 Electrical Equipment for Explosive Gas Atmospheres - selection, installation and maintenance.

It cannot be overemphasised that the person responsible for the Standard library within a company must inform the discipline engineers of any update or superseding of Standards. All too often engineers are left in the dark and are working to out of date Standards.

AS/NZS2381.1 "General Requirements" should be read first, this part along with the other parts relevant to the specific technique are applied in new installations, changes to existing installations whether permanent or temporary, and in maintaining equipment.

The Engineer after referencing the Hazardous Area drawings regarding location, zoning, gas groups and surface temperatures should select the equipment design according to the requirements of AS/NZS2381.1 . An important aspect of this is the comprehension of equipment labelling. (see Table 2).

Table 2

Explosion Protection	Type of Protection	GasGroup	Temperature Classification
Exd-	Flameproof	I (methane - mining only)	T1 -450°C
Exi-	Intrinsically safe	IIA (Propane)	T2-300°C
Exp-	Pressurisation	IIB (Ethylene)	T3-200°C
Exe-	Increased safety	IIC (Hydrogen)	T4-135°C
Exm-	Encapsulation		T5-100°C
Exn-	Non-incendive		T6- 85°C
Exs-	Special Protection
Exo-	Oil Immersed
Exq-	Powder/sand filled
Exv-	Ventilation
Notes The certificate number AUSEx...,ANZEx...or IECEx....must be on the label or the certification may not be acceptable. If the label is headed EEx the equipment is certified to European norms. Standards Australia publish a list of Australian certified equipment, this can be found at www.anzex.com.au. Safe Area Apparatus associated with intrinsically safe circuits is distinguished by the marking "ia", "ib"or"Exia", Ëxib" within brackets. e.g. Ex(ia), Ex(ib), (Exia), (Exib). European equipment is bracketed with square brackets [EExia]. It must be noted that equipment marked with these brackets is no in itself intrinsically safe and thus must not be mounted in a hazardous area without alternative protection!

As an aid to selecting the particular equipment or Australian Standard for a certain zone the easy reference guide Table 3 can be utilised. The relevant Standard pertaining to the selected equipment should then be read.

Table 3

Equipment and Standard Selection It should be noted that AS/NZS2381.1 gives general installation guidelines. When no other standard is detailed in this table there is no specific installation standard for the technique. Thus the installer must refer to the apparatus standard for guideance. In addition the Australian standards should be fully read and understood in line with the competency provisions outlined previously in this document. The standards can be obtained from http://www.sai-global.com/shop/script/Search.asp Zone 0 Exia (Intrinsically Safe) Apparatus Standards AS/NZS 60079.11 AS 2380.7 Installation Standards AS/NZS 60079.14 - Explosive atmospheres - Electrical installations design, selection and erection.  AS/NZS 2381.1 AS 2381.7 AS/NZS 60078.25 Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance  Exma (Encapsulation-level of protection a) Apparatus Standard AS/NZS 60079.18 Installation Standard AS/NZS 60079.14 - Explosive atmospheres - Electrical installations design, selection and erection.  Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance  Exs (Special Protection) Clearly marked for the relevant zone ie., specifically marked for Zone 0 use. Apparatus Standard AS/NZS 1826(Int)  AS/NZS 60079.33 - Explosive Atmospheres - Equipment Protection by Special Protection ‘S’ - The objective of this Standard is to provide requirements and the specific methodology for the assessment, testing and marking of electrical equipment, parts of electrical equipment and Ex components with special protection ‘s’. Installation Standards AS/NZS 60079.14 - Explosive atmospheres - Electrical installations design, selection and erection.  AS/NZS 2381.1 AS 1076.8 Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance OPis (Inherently Safe Optical Radiation)  IEC 60079-28 - Protection of Equipment and Transmission Systems using Optical Radiation OPis (Safe with two faults - refer to the standard for more information) OPsh (Protected fibre optical media with ignition capable beam interlocked with fibre breakage) IEC 60079-28 - Protection of Equipment and Transmission Systems using Optical Radiation OPsh (Safe with additional mechanical protection - refer to the standard for more information) Further information on Fibre Optics in Hazardous Areas Zone 1 All Zone 0 techniques plus Exib (Intrinsically Safe) Apparatus Standard AS2380.7 AS/NZS 60079.11 Installation Standards AS/NZS 60079.14 - Explosive atmospheres - Electrical installations design, selection and erection.  AS/NZS 2381.1 AS 2381.7 AS/NZS 60078.25 Inspection and Maintenance AS/NZS 60079.17 Explosive atmospheres - Electrical installations inspection and maintenance  Exd (Flameproof) Apparatus Standard AS/NZS60079.1 AS 2380.2 Installation Standards AS/NZS 60079.14 - Explosive atmospheres - Electrical installations design, selection and erection.  AS/NZS 2381.1 AS/NZS 2381.2 Electrical equipment for explosive atmospheres - Selection, installation and maintenance - Flameproof enclosure 'd'  Inspection and Maintenance AS/NZS 60079.17 Explosive atmospheres - Electrical installations inspection and maintenance Exe (Increased Safety) Apparatus Standards AS/NZS 60079.7  AS 2380.6 Installation Standards AS/NZS 60079.14 - Explosive atmospheres - Electrical installations design, selection and erection.  AS/NZS 2381.1 AS2381.6 Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance  Exm (Encapsulation) Apparatus Standards AS/NZS 60079.18 Installation Standards AS/NZS 60079.14 - Explosive atmospheres - Electrical installations design, selection and erection.  AS/NZS 2381.1 Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance Exmb (Encapsulation-level of protection b) Apparatus Standard AS/NZS 60079.18 Installation Standard AS/NZS 60079.14 - Explosive atmospheres - Electrical installations design, selection and erection.  AS/NZS 2381.1 Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance Exp (Pressurisation) - when installed to Zone 1 requirements. Apparatus Standard AS2380.4 AS/NZS 60079.2 Installation Standard AS/NZS 60079.14 - Explosive atmospheres - Electrical installations design, selection and erection.  AS/NZS 2381.1 Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance Exv (Ventilation) - when installed to Zone 1 requirements. Apparatus Standards AS 1482 Installation Standards AS/NZS 60079.14 - Explosive atmospheres - Electrical installations design, selection and erection.  AS/NZS2381.1 Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance  Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance  Exs (Special Protection) Clearly marked for the relevant zone ie., specifically marked for Zone 1 use. Apparatus Standard AS/NZS1826(Int) AS/NZS 60079.33 - Explosive Atmospheres - Equipment Protection by Special Protection ‘S’ - The objective of this Standard is to provide requirements and the specific methodology for the assessment, testing and marking of electrical equipment, parts of electrical equipment and Ex components with special protection ‘s’. Installation Standards AS/NZS 60079.14 - Explosive atmospheres - Electrical installations design, selection and erection.  AS/NZS 2381.1 AS 1076.8 Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance Fieldbus Intrinsically Safe Concept (FISCO) Apparatus, Systems and Installation Practice AS/NZS 60079.27 Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance  Exo (Oil Immersion) Apparatus Standard AS/NZS60079.6 Installation Standards AS/NZS 60079.14 - Explosive atmospheres - Electrical installations design, selection and erection.  AS/NZS2381.1 Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance  Exq (Powder Filling) Apparatus Standard AS/NZS60079.5 Installation Standards AS/NZS 60079.14 - Explosive atmospheres - Electrical installations design, selection and erection.  AS/NZS2381.1 Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance  OPis - Inherently Safe Optical Radiation  IEC 60079-28 - Protection of Equipment and Transmission Systems using Optical Radiation - OPis (safe with one fault- refer to the standard for more information) OPpr - Protected Fibre Optical Media with Ignition Capable Beam IEC 60079-28 - Protection of Equipment and Transmission Systems using Optical Radiation - OPpr (with additional mechanical protection - refer to the standard for more information) OPsh (Protected fibre optical media with ignition capable beam interlocked with fibre breakage) IEC 60079-28 - Protection of Equipment and Transmission Systems using Optical Radiation OPsh (Safe without additional mechanical protection - refer to the standard for more information) Further information on Fibre Optics in Hazardous Areas Zone 2 All Zone 0 and 1 techniques plus Exn (Non incendive) Apparatus Standard AS/NZS 60079.15 - Electrical apparatus for explosive gas atmospheres - Construction, test and marking of type of protection, ‘n’ electrical apparatus. Installation Standards AS/NZS 60079.14 - Explosive atmospheres - Electrical installations design, selection and erection. AS/NZS 2381.1 AS1076.7 Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance  Exp (Pressurisation) - when installed to Zone 2 requirements. Apparatus Standard AS2380.4 AS/NZS 60079.2 Installation Standard AS/NZS 60079.14 - Explosive atmospheres - Electrical installations design, selection and erection.  AS/NZS 2381.1 Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance Exv (Ventilation) - when installed to Zone 2 requirements. Apparatus Standard AS 1482 Installation Standard AS/NZS 60079.14 - Explosive atmospheres - Electrical installations design, selection and erection.  AS/NZS 2381.1 Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance Exs (Special Protection) Clearly marked for the relevant zone ie., specifically marked for Zone 2 use. Apparatus Standard AS/NZS 1826(Int) AS/NZS 60079.33 - Explosive Atmospheres - Equipment Protection by Special Protection ‘S’ - The objective of this Standard is to provide requirements and the specific methodology for the assessment, testing and marking of electrical equipment, parts of electrical equipment and Ex components with special protection ‘s’. Installation Standard AS/NZS 60079.14 - Explosive atmospheres - Electrical installations design, selection and erection.  AS1076.8 Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance Ex'o-oil immersion" is a technique used occasionally for switchgear and transformers. There is not widespread use of this technique. Ex'q-powder filling"technique is not common. Fieldbus Non Incendive Concept (FNICO) Apparatus, Systems and Installation Practice AS/NZS 60079.27 Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance  Inspection and Maintenance AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance  OPis - Inherently Safe Optical Radiation  IEC 60079-28 - Protection of Equipment and Transmission Systems using Optical Radiation - OPis (safe in normal operation - refer to the standard for more information) OPpr - Protected Fibre Optical Media with Ignition Capable Beam IEC 60079-28 - Protection of Equipment and Transmission Systems using Optical Radiation - OPpr - (without additional mechanical protection - refer to the standard for more information) OPsh (Protected fibre optical media with ignition capable beam interlocked with fibre breakage) IEC 60079-28 - Protection of Equipment and Transmission Systems using Optical Radiation OPsh (Safe without additional mechanical protection - refer to the standard for more information) Further information on Fibre Optics in Hazardous Areas

On selection of equipment the vendor should be requested to supply a copy of the relevant Certificate of Conformity PRIOR to orders being placed.

The responsible engineer should read the certificate for the following reasons:-

• To ensure it is the correct document for the equipment, (all too often vendors supply incorrect certificates).
• To comply with any "conditions of use" stated on the certificate.

When the certification has been reviewed it should be filed for entry into the verification dossier. The engineer can then proceed with the circuit\system design in accordance with the equipment certificates and relevant Standards.

 

Hazardous Area Installations Verification Dossiers

It is essential that a verification dossier is prepared for all Hazardous Area installations. Included in this dossier should be:-

1. Hazardous Area drawings
2. Certification schedule
3. Equipment certificates
4. The engineering calculations pertaining to Intrinsically Safe loops
5. Cable schedules and Cable routes
6. Special tests to be carried out upon Installation/Commissioning
7. Inspection report on installation
8. Periodic inspection reports.

The dossier must be updated during the life of the plant reflecting any changes which are implemented pertaining to the installation and equipment within the Hazardous Area.

The engineer responsible for the Hazardous Area drawings must be advised of any minor/major piping changes since these could result in changes to the Hazardous Area classification.

A full listing is available in AS2381.1 clause 1.6

 

Electrical Equipment in Hazardous Areas Installation and Maintenance

AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance 

AS/NZS3000 Australian and New Zealand wiring rules and its associated Standards must be read at length and understood by the construction and maintenance engineers. Technicians and fitters should also be conversant with the requirements of the standard.

On a plant which is old or has been poorly maintained it is very important that the Company institutes an inspection to ensure compliance. In order to achieve this it will be necessary to have up to date Hazardous Area drawings and certification schedules. If these drawings are not available they should be produced.

The recommendations of the inspection report should be discussed with both maintenance, installation, design engineers and plant management.

An important clause to remember that no equipment which is in an unsafe condition shall be connected or remain connected to an installation". In other words if there is a non compliance problem fix it or disconnect it.

Electrical staff should be fully conversant with and receive periodical updates in the principles of electrical equipment protection concepts. It is essential that personnel are aware of the certification limitations of test equipment since being portable this equipment is more likely to constitute a hazard in that it can be used in zones for which it is not certified.

Frictional Sparking Risks with Light Metals and their Alloys is very important and often misunderstood. This hazard is due to sparking when light metals and their alloys come into frictional contact with materials which are oxygen carriers, rust being the most common.

NO light metal alloy is permitted in a Zone 0 area. Fixed light metal alloy equipment is permitted in other zones subject to impact protection. Portable equipment of these materials is NOT permitted in Hazardous Areas unless equipment is otherwise protected (i.e. plastic coated or epoxy painted). A frequent breach of regulations can be seen with aluminium foil. aluminium scaffolding, aluminium sunshades, aluminium paint and the "old style" aluminium hard hats.

 

Repair and Overhaul of Electrical Equipment in Hazardous Areas

AS/NZS 3800 - Electrical equipment for explosive atmospheres - Repair and overhaul - This Standard

• specifies requirements for and gives instructions, principally of a technical nature, on the repair, overhaul, reclamation and modification of equipment designed for use in explosive atmospheres;
• is not applicable to maintenance, other than when repair and overhaul cannot be disassociated from maintenance, neither does it give advice on cable entry systems which may require a renewal when the equipment is re-installed;
• prevents overhaul without manufacturer and certificate documentation to types of protection ‘i’ and ‘m’; and
• assumes that good engineering practices are adopted throughout.

Inspection of Electrical Equipment in Hazardous Areas

Inspection of Electrical Equipment prior to/during and periodically after installation is essential. AS2381 reflects the importance that the Standards Australia place on inspection with each of the sections detailing typical "Inspection" schedules. Generally these inspection schedules are combined into an overall schedule for the plant.

AS/NZS 60079.17 - Explosive atmospheres - Electrical installations inspection and maintenance. 

Inspection intervals should not exceed four years.

 

Limitations of Australian Hazardous Area Standards

There are several notable areas which are not covered by Australian Standards these are -

Analyser Houses

Analyser Houses have been in use for many years and to date no Australian Standard has been issued specifically referring to what can be a very hazardous environment. AS2380.4 (Pressurisation) instructs the user to refer to IEC 79-16 for analyser houses which details how to design these enclosures utilising ventilation concepts.

Although not a standard the document "Electrical Installations in Flammable Atmospheres" published by the Royal Society for the Prevention of Accidents has a very useful section on Analyser Houses.

Ignition Fired Gas Engines

This is another complex subject which certainly merits inclusion in a Standard.

Useful References:

Selection, installation and maintenance guidelines for Ignition Systems used in Class 1, Group D, Division 2 locations on Internal Combustion Engines published by the American Gas Association

Gas Fired Boilers in Industrial Hazardous Areas

There are no firm guidelines for the zoning of the above extremely confusing subject which causes great deal of "heartache" to many engineers. It is often difficult to zone an area where there may be for example, open flames protected by flame arrestors and high exhaust temperatures as a fundamental part of the apparatus.

Any engineer who believes that limitations exist in the Standards pertaining to the area in which he is working should first check with the Australian Standards publications catalogue ensuring that Standard on the subject has not been issued.

If no Australian Standard is available then other reference/foreign Standards should be sought. The proposed design should then be discussed and agreed upon by the responsible engineers. Any engineering decisions taken must be fully documented and included in the plant certification dossier.

 

Other Useful Standards and Handbooks

AS/NZS 2229 Fuel dispensing equipment for explosive atmospheres.

 AS/NZS 60079.28:  Protection of equipment and transmission systems using optical radiation. 

Electrical Equipment for Hazardous Areas Handbook HB2007 - from Standards Australia, the main objective of this updated handbook is to provide a basis for understanding the principles involved in the identification of a hazardous area, relevant statutory requirements and the selection and installation, maintenance, testing, overhaul and repair of appropriate electrical equipment. This handbook also provides a basic introduction to the relevant Australian, New Zealand, Joint (Australian/New Zealand) and International Standards dealing with hazardous areas.

 

Gas Detection

AS/NZS 60079.29.1 - Explosive atmospheres - Gas detectors - Performance requirements of detectors for flammable gases.

AS/NZS 60079.29.2 - Explosive atmospheres - Gas detectors - Selection, installation, use and maintenance of detectors for flammable gases and oxygen.

AS/NZS 60079.29.4 - Explosive Atmospheres - Gas Detectors - Performance requirements of open path detectors for flammable gases.

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

 

Static Electricity in Hazardous Areas

IEC 60079-32 - Guidance for the Avoidance of HazardsDue to Static Electricity - Mike O’Brien - The International Electrotechnical Commission has published a new Technical Specification called IEC 60079-32-1: “Explosive atmospheres - Part 32-1: Electrostatic hazards - Guidance”. This Technical Specification is a guidance document which is the latest addition to the IEC series of 60079 “Explosive Atmospheres” standards that are designed to limit fires and explosions caused by electrical malfunctions within hazardous locations. The 168 page document is the first of two documents to be published by the IEC under the “60079-32” designation and is intended to aid the designers and users of process equipment minimise the risk of incendive electrostatic discharges within potentially explosive atmospheres. It covers a broad range of process scenarios that can lead to the generation of electrostatic charges, provides examples of what measures can be taken to reduce charge generation and accumulation and outlines how process equipment should be grounded and bonded. The second part, IEC 60079-32-2, is entitled “Electrostatics hazards - Tests” and outlines test methods to determine factors like surface resistance, earth leakage resistance, powder resistivity, liquid conductivity, capacitance and the incendivity of electrostatic discharges - from Newson Gale.

Standards for the Control of Static Electricity in Hazardous Areas - Mike O’Brien - There are several internationally recognised standards that provide guidance on ways to limit electrostatic hazards enabling those responsible for worker health and safety minimise the risk of incendive static discharges. Hazardous area operators who can demonstrate compliance with these standards will go a long way to providing a safe working environment and preventing the ignition of ignitable atmospheres - from Newson Gale.

 

Foreign Ex Standards

It should not be generally required to refer to foreign Standards in association with new installations except in special circumstances which are detailed in the following Foreign Certification section. However on older installations it is quite likely that foreign, often American equipment, has been installed. It is therefore necessary to understand the labelling of this equipment to ensure its suitability for the zone in which it has been installed.

Comparisons of Standards are detailed in Tables 4, 5 and 6. Care must be taken with these comparison tables detailed since although generally true some countries have gases/materials in different classes/groupings to others. Classification techniques also vary from country to country.

Table 4

Nature of Hazard
AUSTRALIA AS/NZS60079.10 Flammable gases, liquids and vapours Note Classes no longer exist	USA NEC* Class I**
*NEC - National Electric Code **Class 1 (USA) - Locations which are hazardous because of the presence of flammable gases, vapours and mists

Table 5

Area Classification
AUSTRALIA AS2430/60079 Zone 0 Zone 1 Zone 2	USA NEC Division 1* Division 1 Division 2**	IEC/CENELEC IEC79/CENELEC31 Zone 0 Zone 1 Zone 2	GFR VDE Zone 0 Zone 1 Zone 2
*Division 1 USA - Areas which are likely to contain flammable atmospheres in normal operation. **Division 2 - areas which are likely to contain flammable atmospheres only in abnormal operation.

Table 6

Hazardous Materials - Gas Grouping
Australia	USA NEC	IEC/CENELEC 60079	GFR VDE 0171	Gas Type
AS 2430/ 60079
IIA IIB IIC IIC	D C B A	IIA IIB IIC IIC	*(1)IIA *(2)IIB *(3a)IIC *(3b, c, n)	Propane etc Ethylene etc Hydrogen Acetylene
*Superseded standard

Table 7

Surface Temperature Classes
Australia AS/NZS60079	USA NEC	IEC/CENELEC 60079	GFR VDE
T1 (450°C)	T1 (450°C)	T1	*(G1) T1
T2(300°C)	T2 (300°C) T2A(280°C) T2B(260°C) T2C(230°C) T2D(215°C)	T2	*(G2) T2
T3(200°C)	T3 (200°C) T3A(l 80°C) T3B(165°C) T3C(l60°C)	T3	*(G3n) T3
T4 (135°C)	T4 (135°C) T4A(120°C)	T4	*(G4) T4
T5 (100°C)	T5 (100°C)	T5	*(G5) T5
T6 ( 85°C)	T6 (85°C)	T6	T6
*() Superseded Standard

 

Foreign Certification

If available, equipment with Australian/International AUSEx/ANZEx or IECEx certification should be selected and installed in compliance with Australian Standards. To select foreign certified equipment on the basis of lower cost is false economy since documentation costs are likely to exceed any savings.

Sometimes however AUS/ANZ/IECEx certified equipment is not available and alternative equipment must be sought. 

Certification of electrical equipment for use in hazardous areas is mandatory due to legislation that calls up AS/NZS2381.1. 

AS/NZS2381.1-2005, Clauses 2.3 and 2.4.2 require that electrical equipment installed in hazardous areas be protected by a suitable explosion protection technique complying with either:

• the relevant Australian Standard; or
• the relevant IEC Standard

as detailed in Table 2.1 of AS/NZS2381.1-2005.

The Standard further states that, “Certified apparatus shall be used as it provides the necessary assurance that apparatus meets the requirements of the appropriate Standard.”   Acceptable certification shall be covered by a certificate of conformity issued in accordance with:

• the ANZEx scheme
• the IECEx scheme
• or another Type 5 scheme complying with ISO/IEC Guide 67, and meeting the requirements contained in AS/NZS2381.1 App. G.

Certificates under the AUSEx scheme are still valid.

Thus it is the certificate of conformity issued in accordance with the ANZEx, AUSEx or IECEx scheme, which determines the acceptability of electrical equipment for installation in hazardous areas.

‘Other’ Ex Certification/Approval Systems

In circumstances when the user needs to use ATEX, FM, CSA, UL or other Ex equipment not certified to the ANZEx/AUSEx or IECEx schemes, the equipment and its installation must provide an equivalent level of safety to the ANZEx/AUSEx or IECEx schemes, and the user must obtain a Conformity Assessment document (CAD).  The CAD provides evidence that a certificate of conformity to an alternative standard can be demonstrated to provide an equivalent level of safety to AS/NZS or IEC Standards. This normally requires a comparison of the relevant standards and verification that testing has been conducted by a third party. The legal owner must provide justification for the use of the equipment and document the acceptance in the dossier.  In some instances, there may be additional legislated requirements for acceptance of apparatus certified to alternative standards.

 

Conclusion

The Australian Standards are important reference documents for personnel involved in any way with electrical equipment in Hazardous Areas.

Personnel who (a) where possible use Australian certified electrical equipment, (b) provide full documentation in the form of a verification dossier and (c) read, digest and utilise the standards and other Hazardous Area documentation to the best of their ability can be confident that their plant has very few, if any, electrical non-compliance problems.

References

• Garside: Intrinsically Safe Instrumentation - A Guide", published by Safety Technology Ltd, UK, 1982.
• H.G. Bass: "Intrinsic Safety", published by Quatermaine House Ltd, UK, 1984.
• SIRA Ltd: "Safety of Electrical Instrumentation in Potentially Explosive Atmospheres", unpublished course notes.
• ROSPA: "Electrical Installation in Flammable Atmospheres",published by ROSPA, UK, 1972.
• A.P.I. recommended practice RP500A, B and C. A.G.A. Selection, Installation and Maintenance Guidelines for Ignition Systems Used in Class 1, Group D, Division 2 Locations on Internal Combustion, Spark Ignited Gas Engines. CPR-85-4-1
• Explosion Protection Technology website http://www.eptech.com.au. 

 

Other Useful Information

List of Current Hazardous Area and Electrical Equipment in Hazardous Areas IEC Standards - from IECEx.

Overview of the Various National and Regional Regulations Governing Hazardous Area Certified Products - Mike O’Brien - The task of selecting an electrical system destined for use in a hazardous location can lead to a time consuming navigation through a myriad of approval certificates with different acronyms, product labelling details and an investigation into what the markings on the label(s) actually represent. This article provides an overview of the various national and regional regulations governing hazardous area certified products, take a brief look at the standards against which they are assessed and examine if there is any scope for creating a “common language” for users of hazardous area equipment that may facilitate a future in which class leading hazardous area equipment, regardless of origin, is acceptable to the relevant regulatory body of the country in which the hazardous area operator is located - from Newson Gale.

Standards Australia - Australian Standard Bursting disks and bursting disk devices - Guide to application, selection and installation

Section 1. Scope and General

1.1 Scope

This Standard provides guidance on the application, selection and installation of bursting disks and bursting disk devices.

Information which the purchaser may provide to assist in the design or the selection of bursting disks and bursting disk devices is shown in Appendix A.

The information which may be used for identification and also that which may be marked on bursting disks and bursting disk devices is shown in Appendix B.

Equations for the calculation of the discharge capacity for single phase flow are shown in Appendix C.

1.2 Definitions

For the purpose of this Standard, the definitions below apply.

1.2.1 Bursting pressure - the value of the pressure differential across the disk at which a bursting disk device functions. (See Note to Clause 1.2.2.)

1.2.2 Specified bursting pressure - the pressure, quoted with a coincident temperature, specified by the user or his agent when defining the disk requirement.

NOTE: The words maximum and minimum may be used with the terms bursting pressure and specified bursting pressure

1.2.3 Average bursting pressure - the arithmetic average value, at the coincident temperature, of the test bursts carried out on a batch of disks.

1.2.4 Coincident temperature (bursting pressure) - the temperature used in conjunction with bursting pressure.

1.2.5 Operating temperature - the average temperature of the disk and the surrounding parts during normal operation.

1.2.6 Bursting tolerance - the maximum variation of test results in equal positive and negative quantities or percentages related to the average bursting pressure. Where a zero manufacturing range is stated, the tolerance is applied directly to the specified bursting pressure.

1.2.7 Manufacturing range - a range of pressure within which the average bursting pressure of a batch of bursting disks falls in order to be acceptable for a particular application.

1.2.8 Performance tolerance - a range of pressure in positive and negative quantities or percentages which includes both manufacturing range and bursting tolerance at a coincident temperature, which is applied directly to the specified bursting pressure.

1.2.9 Foil - the sheet or strip used for the manufacture of metallic bursting disks.

1.2.10 Batch - a group of bursting disks of the same type, size, average bursting pressure, and coincident temperature, manufactured from material of the same identity and properties made as a single group.

1.2.11 Bursting disk device - a non-reclosing pressure-relief device actuated by differential pressure and designed to function by the bursting or venting of the bursting disk.

1.2.12 Bursting disk assembly - the complete assembly of components which are installed in the bursting disk holder to perform the desired function.

1.2.13 Bursting disk - the pressure-containing and pressure-sensitive element of a bursting disk device.

1.2.14 Bursting disk holder - that part of a bursting disk device which retains the bursting disk assembly in position.

1.2.15 Backpressure - the static pressure existing at the outlet of a bursting disk device at the time the device is required to operate. It is the result of pressure in the discharge system from other sources or as a result of vacuum on the upstream side.

1.2.16 Backpressure support - that component of a bursting disk assembly which prevents the failure of the disk due to backpressure differential.

NOTE: A backpressure support which is intended to prevent the failure of the disk when the system pressure falls below atmospheric pressure is sometimes referred to as a vacuum support.

1.2.17 Baffle plate - a plate attached to vent side of a bursting disk device or system to redirect discharge or redirect discharge or reduce recoil.

1.2.18 Muffled outlet - a component of a bursting disk device which disperses the discharge.

1.2.19 Stiffening ring - an integral component of the bursting disk assembly used primarily for the stiffening of fragile disks.

1.2.20 Coating - a layer of metallic or non-metallic material applied by brush, spray, dipping, fluidised bed, or other similar method to components of a bursting disk device.

1.2.21 Lining - an additional sheet or sheets of material forming part of the bursting disk assembly or holder. The lining can be metallic or non-metallic.

1.2.22 Plating - a metal layer applied to a disk or holder by a plating process.

1.2.23 Excess flow valve - a device which permits limited flow. When this flow is exceeded the valve closes.

1.2.24 Conventional domed bursting disk - a bursting disk which is domed in the direction of the bursting pressure and designed to fail in tension. (See Figures 2.2 and 2.3).

1.2.25 Slotted lined bursting disk - a conventional domed bursting disk made up of two or more layers, one of which is slit or slotted so as to reduce its strength and to control the bursting pressure of the bursting disk. (See Figure 2.4).

1.2.26 Reverse domed bursting disk - a bursting disk which is domed against the direction of the bursting pressure and designed to fail by buckling, bending or shearing forces. (See Figure 2.5).

1.2.27 Graphite bursting disk - a bursting disk manufactured in graphite and designed to fail by bending or shearing forces.

1.2.28 Temperature shield - a device which protects a bursting disk from excessive temperature.

1.2.29 Bursting disk device discharge area - the area which is the geometric minimum cross-sectional flow area of the bursting disk device which is used to calculate the theoretical flow capacity of the bursting disk device.

NOTE: Possible reduction of the cross-section, for example by backpressure supports, catching devices, or parts of the bursting disk which remain after bursting, has to be considered.

1.2.30 Bursting disk device discharge capacity - the rate at which a bursting disk device can discharge fluid after bursting or venting of the bursting disk.

1.2.31 Service life - the time period beginning at the installation of a bursting disk assembly and ending at either replacement or burst.

1.2.32 Operating pressure - the pressure to which the bursting disk is exposed during normal operation.

1.2.33 Inspecting Authority - the Authority having statutory powers to control the design, manufacture, and use of bursting disks and bursting disk devices in the State or Territory in which they are to be used except that where the devices are not subject to such statutory jurisdiction the Inspecting Authority is the purchaser, or the person or organisation named as such in the purchase order.

1.2.34 Inspector - either the Inspecting Authority or a person or an organisation appointed or approved by the Inspecting Authority for the purpose of inspecting bursting disks and bursting disk devices in accordance with this Standard, except that in regard to materials ‘Inspector’ be a person acting under the express written authority of the purchaser of the material.

1.2.35 Approved and approval - approved by or with the approval of the Inspecting Authority.

1.2.36 Shall - indicates that a statement is mandatory.

1.2.37 Should - indicates a recommendation.