THE BASICS OF EXPLOSION PROTECTION:

Many industrial processes utilising flammable materials have the potential to give rise to a potentially explosive atmosphere. Potentially explosive atmospheres exist where there is a risk of explosion due to mixtures of gas & air, vapour & air, dust & air or other flammable combinations. Where a potentially explosive atmosphere is present, in order to protect plant and personnel, measures must be taken to ensure that electrical equipment cannot ignite that potentially explosive environment. It is therefore necessary to eliminate all sources of ignition which might ignite such mixtures.

ATEX Directive – EU Legislation:

On 1st July 2003 the ATEX Directive came into effect for all EU countries. This new Directive provides the technical requirements to be applied to equipment intended for use in Potentially Explosive Atmospheres. This Directive requires that a complete and documented analysis of all sites which may be a Potential Explosive Atmosphere. This assessment helps determine the actions required, such as the elimination of ignition sources or Area Classification (Zoning).

Hazardous Area Equipment has been around for many years, where electrical equipment was certified for use in potentially explosive atmospheres. The ATEX Directive imposes much stricter controls on the manufacturers of hazardous area equipment and compliance with the directive is mandatory within the EU. Under ATEX existing equipment in the field has to comply with the Directive. Manufacturers who apply the provisions of the Directive and affix the CE marking are able to sell their equipment anywhere in Europe.

The ATEX Directive covers: -

• Equipment and products that have their own source of potential ignition.
• Protective systems - products that control the effects of incipient explosions.
• Safety devices - products that may be outside a potentially explosive atmosphere but that have an explosion safety function.
• Components - products that are intended to form parts of equipment or protective systems.

To ensure compliance, equipment must meet the essential requirements as specified in the Directive and be marked with the CE marking.

North America and Europe each have their own certification and approval systems. For example, North American certifying bodies divide risk assessment into Classes & Divisions, CENELEC and IEC, the certifying bodies (Pre-ATEX) employed in Europe, use a system of dividing into ‘Zones’ - Zones 1,2,3 for Gas and Zones 20,21,22 for Dust. As stated above, since July 2003, it is now mandatory in E.U. countries products comply to the ATEX Directive approval system which divides environments into ‘Categories’ - Category 1G, 2G or 3G for Gas and 1D, 2D or 3D for Dust.

Note: Many countries outside Europe and American use the IEC Standards as their own national standards.

The purpose of this section is to help identify the key criteria which is applied to the selection and installation of appropriate equipment. This section is intended as a guide only and we advise that expert guidance should always be sought prior to putting equipment into service in a potentially explosive atmosphere or having that equipment maintained or repaired.

There are a number of regulations, guidelines and standards which determine the design, installation and maintenance of equipment to be located in potentially explosive atmospheres. There are differences between European and American certification, approval and general practices; therefore individual codes of practice and standards should always be consulted for exact requirements.

Selection of Equipment:

1. Area Classification or ‘Zoning’:

   Where ignition sources cannot be eliminated and a flammable gas or dust area may be present, it is important to assess the extent and duration of the risk to select the correct equipment. This is normally referred to as ‘Zoning’.

   The purpose of ‘Zoning’ is to provide the basis for correct selection of a protection concept. Areas are classified depending on the properties of the flammable vapours, liquids, mists, gases or combustible fibres/dusts that may be present in the environment and the likelihood that a combustible concentration of that gas or dust is present.

   Zone Definition	ATEXGroup II	CENELEC / IEC	UL (North American)
   An area in which an explosive mixture is continuously present or present for long periods. Estimate: > 1000 hours / year	Category 1G (Gases) Category 1D (Dusts)	Zone 0 (Gases, vapours or mists) Zone 20 (Dusts)	Class 1 Division 1 (Gases) Class II Division 1 (Dusts)
   An area in which an explosive mixture is likely to occur in normal operation. Estimate: > 10 hours / year and < 1000 hours / year	Category 2G (Gases) Category 2D (Dusts	Zone 1 (Gases, vapours or mists) Zone 21 (Dusts)	Class I Division 1(Gases) Class II Division 1 (Dusts)
   An area in which an explosive mixture is not likely to occur in normal operation. Estimate: < 10 hours / year	Category 3G (Gases) Category 3D (Dusts)	Zone 2 (Gases, vapours or mists) Zone 22 (Dusts)	Class I Division 2 (Gases) Class II Division 2 (Dusts) Class III Division 1 (Fibres)Class III Division 2 (Fibres)

   
   
   

2. Gas Groups:

   Gases are divided in two main gas groups:

   Group I: Concerned with underground mining where coal dust and methane are present. Group 2: Concerned with surface industries gases & dust. They are subgrouped according to volatility - IIA being the least volatile and IIC the most volatile.

   
   

   Typical Gas/Material	European/IEC Gas Group	North American Gas Group
   Methane	I	-
   Acetylene	IIC	A
   Hydrogen	IIC	B
   Ethylene	IIB	C
   Propane	IIA	D
   Metal	-	E
   Coal Dust	-	F
   Grain Dust	-	G

   
   
   

3. Temperature Classification:

   The temperature at which a gas will ignite spontaneously with no other source of ignition is the auto-ignition temperature. Auto-ignition can occur when hot surfaces are in contact with explosive atmospheres. There is a classification used to indicate the maximum surface temperature that a piece of electrical equipment could reach when in service. The maximum surface temperature is generally based on a surrounding maximum ambient temperature of 40° C (102° F). The "T"-class of a piece of equipment can be compared to the auto-ignition temperature of gases that may come into contact with it and hence a decision can be made as to the suitability of the equipment to be used in that area. The aim is to avoid ignition of flammable releases that occur in the normal operation of facilities and reduce to an acceptable minimum the probability of a flammable atmosphere and an ignition sources occurring at the same time.

   Categorisation of Gases & Vapours (European/IEC):

   5

   Temperature Classification	Maximum Surface Temperature C°	IIA	IIB	IIC
   T1	450°C	Methane Ammonia	-	Hydrogen
   T2	300°C	Butane	Ethylene	-
   T3	200°C	Kerosene Cyclohexane	-	-
   T4	135°C	Acetaldehyde	Diethyl Ether	-
   T5	100°C	-	-	-
   T6	85°C	-	-	Carbon Disulphide

   
   
   

4. Standards and Methods of Protection:

   Different techniques are used to prevent electrical equipment from being a source of ignition. The following table shows the concepts and standards for electrical apparatus for gases, vapours and mists.

Given the above information, selection of the electrical equipment is made according to:

• Classification of the Hazardous Area
• Temperature class or ignition temperature of the gas, liquid, vapour, mist, dust or fibre.
• The gas, vapour, dust classification in relation to the Group .
• External influences and ambient temperature.
• Geographical destination of the goods (certifying body).

Note: Apparatus According to Zones/Categories:

Zone 0 / Category 1	Ex ia (Intrinsically Safe products only)
Zone 1 / Category 2	Any type of protection suitable for Zone 0 Plus Ex d, Ex ib, Ex p, Ex e, Ex q and Ex m.
Zone 2 / Category 3	Any type of protection suitable for Zone 0 or 1 Plus Ex n, Ex N and Ex 0

The system for defining the levels and methods of protection has been defined and codified. This allows manufacturers to design apparatus of a uniform type and to have it tested by certification authorities for compliance with standards.

IEC & CENELEC marking is set out as - e.g. " EExia IIC T4 "

E	Ex	ia	IIC	T4
Certified to CENLEC Standard	Explosion Protected	Protection Method	Gas Group	Temperature Certification

ATEX marking (Mandatory for EU Market) is set out as - e.g. " CE Ex II 2G "

CE	Ex	II	2	G	D
CE marking which certifies conformity	European Explosion Protection Mark	Equipment Group (ie Surface)	Equipment Category	Gas or Vapour	Dust

Equipment Certification and Marking:

Only appropriately certified and marked equipment should be used in hazardous areas. All Apparatus and Components should be clearly marked with the visible information. In addition the Code, Type of protection, Gas Group and Temperature Class described above the following information is marked on all equipment:

• Manufacturer, Model and Serial Number
• Certifying Body and Certificate Number
• CENELEC and Test House Symbols
• Electrical Rating

Ingress Protection:

The IP code of a piece of equipment details the Ingress Protection in accordance with the IEC 529 and EN 60529 standards. It is denoted by two digits, the first applies to solids and the second to liquids. For example a piece of equipment with Ingress Protection IP 67 is dust tight and protected against the effects of immersion.

FIRST NUMERAL: Protection against solid bodies:		SECOND NUMBERAL: Protection against Liquids:
No Protection	0	0	No Protection
solid objects up to 50mm e.g. hands	1	1	Vertically dripping water
Solid objects up to 12mm e.g. fingers	2	2	Vertically dripping water (when enclosure is angled by up to 15°
Solid ojects up to 2.5mm e.g. tools	3	3	Water spray
Solid Objects over 1mm e.g. wires	4	4	No Protection
Dust Protected	5	5	Water jets
Dust-tight	6	6	Heavy seas
n/a	n/a	7	Effects of Immersion
n/a	n/a	8	Indefinite Immersion

Summary of References to harmonised standards under ATEX Directive 94/9/EC:

This list is not exhaustive and is subject to change.

CENELEC EN 1127-1: 1997	Explosive Atmospheres – Explosion prevention and protection – Part 1: Basic concepts and methodology
CENELEC EN 13237:2003	Potentially Explosive Atmospheres – Terms & definitions for equipment and protective systems intended for use in potentially explosive atmospheres.
CENELEC EN 13463-1:2001	Non-electrical equipment for potentially explosive atmospheres – Part 1: Basic methodology and requirements
CENELEC EN 13673-1:2003	Determination of the maximum pressure and the maximum rate of pressure rise of gases and vapours – Part 1: Determination of the maximum explosion pressure.
CENELEC EN 13821:2002	Potentially Explosive Atmospheres – Explosion Prevention and protection – Determination Of minimum ignition energy of dust/air mixtures.
CENELEC EN 13980:2002	Potentially Explosive Atmospheres – Application of Quality Systems
CENELEC EN 50014:1997	Electrical Equipment for potentially explosive atmospheres - General Requirements. Amendment A1: Amendment A2:
CENELEC EN 50015:1998	Oil Immersion ‘o’
CENELEC EN 50017:1998	Powder Filling ‘q’
CENELEC EN 50018:2000	Flameproof Enclosure ‘d’. Amendment A1: 2000
CENELEC EN 50019:2000	Increased Safety ‘e’
CENELEC EN 50020:2002	Intrinsic Safety ‘i’
CENELEC EN 50021:1999	Electrical Apparatus ‘n’
CENELEC EN 50054: 1998	Electrical Apparatus for the detection & measurement of combustible gases. General Requirements & methods.
CENELEC EN 50057:1998	Electrical Apparatus for the detection and measurement of combustible gases. Performance requirements for Group II1 apparatus indicating up to 100% lower explosive limit.
CENELEC EN 50104:1998	Electrical Apparatus for the detection & measurement of oxygen – Performance requirements & test methods
CENELEC EN 50241:1999	Specification for open path apparatus for the detection of combustible or toxic gases and Vapours. Part 1: General requirements and test methods.
CENELEC EN 50241:1999	Specification for open path apparatus for the detection of combustible or toxic gases or vapours. Part 2: Performance requirements for apparatus for detection of combustible gases.
CENELEC EN 50281-1-1:1998	Electrical apparatus for use in the presence of combustible dust – Part 1-2 Electrical apparatus protected by enclosures – Construction and testing. Amendment A1:2002
CENELEC EN 50281-1-1:1998	Electrical apparatus for use in the presence of combustible dust – Part 1-2 Electrical apparatus protected by enclosures – Construction and testing. Amendment A1:2002
CENELEC EN 50284:1999	Special requirements for construction, test and marking of electrical apparatus of equipment Group II, Category 1G.

IEC Standards & Codes:

IEC 60079-0	General Requirements
IEC 60079-6	Oil Immersion ‘o’
IEC 60079-2	Pressurisation ‘p’
IEC 60079-5	Flameproof Enclosure ‘d’
IEC 60079-7	Increased Safety ‘e’
IEC 60079-11	Intrinsic Safety ‘i’
IEC 60079-15	Electrical Apparatus ‘n’
IEC 60079-18	Encapsulation ‘m’
IEC 60079-14	Electrical installations in hazardous areas (other than mines)
IEC 61892-7	Mobile and fixed offshore units – electrical installation, Part 7: Hazardous Areas.
IEC 612141-1-2	Electrical apparatus in the presence of combustible dust.
Proposed Change to IEC 61241-14	Part 1-2: Electrical apparatus protected by enclosures and surface temperatures.
IEC 60079-17	Inspection and maintenance of electrical installations in hazardous areas (other than mines)
IEC 61241-17	Electrical apparatus for use in the presence of combustible dust atmospheres – Part 17: Inspection and maintenance.
IEC 61508	Functional Safety of electrical/electronic/programmable electronic safety-related systems

For most current information visit:

• European (ATEX) Directive: www.europa.eu.int/comm/enterprise/atex/idex.htm
• European (CENELEC) Standards: www.cenelec.org
• International (IEC) Standards: www.iec.ch

Further Reading:

Article 137 of Directive 89/391/EC 28/01/00 establishes minimum requirements for Health & Safety of workers defining:

• Obligations of the employees re. the prevention and protection against explosions
• Assessment obligations re. the assessment of explosion risks.
• General obligations re. the safety and health of worker.
• Requirements for explosion protection documents.

Section II, Article 7 of the Directive: In places where potentially explosive atmospheres may occur in such quantities as to endanger the health and safety of workers, the point of entry must be marked.