Equipment Safety, Approvals, and Standards. UK, Europe and North America
Areas where there is the possibility of the presence of an explosive mixture of flammable gas, vapour, or dust and air are reffered to as ‘hazardous’, and other areas as ‘safe’ or ‘non hazardous’. Any electrical equipment used in hazardous areas, including gas detection equipment, must be specially tested and approved to ensure that, in use even under a fault condition, it cannot initiate an explosion.
Crowcon equipment meets European, American and other international Standards and Directives for electrical equipment used in hazardous areas.
European Approvals
CENELEC
CENELEC is the European Committee for Electrotechnical Standardization. It has been officially recognized as the European Organization in its field by the European Commission in Directive 83/189 EEC. CENELEC uses IEC (International Electrotechnical Commission) standards as a reference and harmonizes them with all the European Community countries (see below)
ATEX Directive
ATEX, (derived from Atmosphere Explosif) is the name given to the framework for controlling explosive atmospheres and the standards of equipment and protective systems used in them. ATEX consists of Directives and is a continuance of CENELEC standards. It addresses issues that were not addressed with the original EN standards such as dust hazards. It is intended that these common standards should completely remove trade barriers within the European Community.
ATEX requires employers to eliminate or control the risks from dangerous substances. Site operators must ensure that plant, equipment, protective systems and any associated connecting devices must only be brought into service if the explosion protection document indicates that they can be safely used in an explosive atmosphere. ATEX is based on the requirements of two European Directives.
1) Directive 99/92/EC (also known as ‘ATEX 137’ or the ‘ATEX Workplace Directive’) on minimum requirements for improving the health and safety protection of workers potentially at risk from explosive atmospheres.
2) Directive 94/9/EC (also known as ‘ATEX 95’ or ‘the ATEX Equipment Directive’) on the approximation of the laws of Members States concerning equipment and protective systems intended for use in potentially explosive atmospheres. Directive 94/9/EC divides the equipment and protective systems which it covers into equipment groups and categories; this Directive provides for a classification by the employer of the places where explosive atmospheres may occur in terms of Zones and determines which equipment and protective systems groups and categories should be used in each Zone. See below.
Classification of hazardous areas
Hazardous places are classified in terms of zones on the basis of the frequency and duration of the occurrence of an explosive atmosphere.
Areas subject to flammable gas hazards are classified as either Zone 0, Zone 1 or Zone 2.
Areas subject to flammable dust hazards are classified as either Zone 20, Zone 21 or Zone 22.
Note: Layers, deposits and heaps of combustible dust must be considered as any other source which can form an explosive atmosphere.
A description of each Zone is shown on the table on the page below.
Equipment Categories Associated with the ATEX Directive
The ATEX Directive identifies two groups of equipment.
Group 1 equipment is intended for use in mining applications, divided into categories M1 and M2. M1 identifies equipment that must continue to operate when a potentially explosive atmosphere is present. M2 identifies equipment that does not operate when a potentially explosive atmosphere is present.
Group 2 is intended for all other situations above ground (Surface Industries). and is divided into categories 1, 2 and 3. Category 1 equipment is intended for use in Zone 0 environments. Category 2 equipment is intended for use in Zone 1 environments. Category 3 equipment is intended for use in Zone 2 environments.
It is mandatory for manufacturers to obtain an EC Type Examination Certificate from a notified body if they are manufacturing electrical equipment in Categories 1 and 2 and M1 and M2.
ATEX Category | Classification | Zone - Gas or Dust |
1 | An area in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas vapour, mist or dust is present continuously or for long periods or frequently. | Gas: Zone 0 Dust: Zone 20 |
2 | An area in which an explosive atmosphere consisting of a mixture with air or flammable substances in the form of gas, vapour, mist or dust is likely to occur in normal operation occasionally. | Gas: Zone 1 Dust: Zone 21 |
3 | An area in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour, mist or dust is not likely to occur in normal operation but, if it does occur, will persist for a short period only. | Gas: Zone 2 Dust: Zone 22 |
Explosion Protection
In equipment design various protection techniques are employed to prevent explosions. Examples are given in the table below.
Protection | Method | Code | Zone | ATEX Category | Division (North America) |
Intrinsically safe "ia" or "ib" | Limit energy of sparks & temperature. This includes one (b) or two (a) electrical faults that may increase the surface temperature above the "T" rating | Ex ia     Ex ib | 0,1,2     1,2 | 1,2,3     2,3 | 1,2     1,2 |
Special "s" | Any method which can be demonstrated to be safe. | Ex s | 0,1,2 | 1,2,3 | 2 |
Flameproof "d" Powder/Sand "q" | Construstion contains explosion & extinguishes the flame | Ex d Ex q | 1,2 1,2 | 2,3 2,3 | 1,2 1,2 |
Increased Safety "e" Non Sparking "n" | No arcs, hot surfaces, sparks by increased insulation & restricted ingress of moisture | Ex e Ex n | 1,2 2 | 2,3 3 | 2 2 |
Pressurized "p" | Continuous flow of air or inert gas or positive static pressure to keep flammable gas away from any ignition source or hot surface | Ex p | 1,2 | 2,3 | 1,2 |
Encapsulation "m" | Encapsulating electrical components with resin | Ex m | 1,2 | 2,3 | 2 |
Temperature Classification
To ensure that there is no risk of ignition due to hot surfaces, equipment is classified with regard to the maximum surface temperature of any part of the equipment while in operation or due to a fault based, on the ambient temperature of 40oC. This is known as the "T" rating. Equipment must be selected with a suitable temperature classification such that it’s maximum surface temperature does not exceed the ignition temperature of the gases and vapours present where the equipment is to be installed.
Gas Group, Apparatus Group and Temperature Rating
Gases are grouped together based on the amount of energy required to ignite the explosive mixture of gases with air. Equipment is classified into groups according to the gases and vapours for which it is suitable.
Gas | Apparatus Group | Max. Surface Temperature oC | "T" Rating |
Methane | I Mining M1 & M2 | 450 | T1 |
Propane | IIA | 300 | T2 |
Ethylene | IIB | 200 | T3 |
Hydrogen | IIC | 135 | T4 |
Acetylene | IIC | 100 | T5 |
Any Gas | II | 85 | T6 |
Markings
The ATEX Directive requires certified products to be marked with the CE mark (confirms compliance with mandatory EMC regulations and the Low Voltage Directive for equipment containing mains voltages), the ‘EX’ mark (indicates that the equipment is designed for use in a hazardous area) and the equipment code (confirms the group, protection concept gas group and temperature classification for which the product is certified).
CE Mark
1180 (1180= Crowcon’s Notified Body Number)
ATEX Group and Category
Example Product Label
Note: Tamb (Ta) denotes the ambient temperature range for which the product is certified (ie will not cause an ignition); it does not indicate the operating temperature of the product.
Approval Bodies
There are many accredited approval bodies that test products and audit quality procedures to verify that products comply with the requirements of mandatory directives such as ATEX. For services relating to ATEX and IECEx approvals Crowcon uses Baseefa, Sira and UL/Demko.
For services relating to North American approvals Crowcon uses UL (Underwriters Laboratories), and CSA (Canadian Standards Association)
North American Approvals
As a result of North America, Canada and Europe moving towards harmonization the National Electric Code (NEC) and the Canadian Electric Code (IEC) now recognise the use of the European Zone system for classification of hazardous areas. NEC’s Article 505 has basically created an Americanized version of the International Electrotechnical Commission (IEC, See below) and CENELEC Zone system. NEC 505 is not the same but it fits the IEC European Zones into it while maintaining NEC protection techniques. In North America, hazardous areas are separated by classes, divisions, zones and groups to define the level of safety required for equipment installed in these locations. Classes define the general form of the flammable materials in the atmosphere. Divisions define the probability of the presence of flammable materials. Zones define the location as in Europe and Groups classify the exact flammable nature of the material.
ClassesÂ
Class | Description |
1- Gases & Vapours | Flammable gases or vapours are present in the air in quantities sufficient to produce explosive or ignitable mixtures. |
2- Dusts | Combustible or conductive dusts are present. |
3- Fibres & Materials | Ignitable fibres or materials producing combustible particles are present, but not likely to be in suspension in sufficient quantities to produce ignitable mixtures. (Group classifications are not applied to this class.) |
Divisions
Area Classification
Process plants are divided into Zones (European and IEC method) or Divisions (North American method) according to the likelihood of a potentially explosive atmosphere being present.
Zones
European, IEC & NEC 505 Classification | Definition of zone or division | North American Classification |
Zone 0-Gases Zone 20-Dusts | An area in which an explosive mixture is continuously present or present for long periods | Class I Division 1 (gases) Class II Division 1 (dusts) |
Zone 1- Gases Zone 21-Dusts | An area in which an explosive mixture is likely to occur in normal operation | Class I Division 1 (gases) Class II Division 1 (dusts) |
Zone 2- Gases Zone 22-Dusts | An area in which an explosive mixture is not likely to occur in normal operation and if it occurs it will exist only for a short time. | Class I Division 2 (gases) Class II Division 2 (dusts) |
Gas and Dust Groups
Substance | Group | CENELEC/ IEC/NEC500 |
Acetylene | Group A | 11C |
Hydrogen | Group B | 11C |
Ethylene | Group C | 11B |
Propane | Group D | 11A |
Methane | Group D | - |
Metal Dust | Group E | - |
Coal Dust | Group F | - |
Grain Dust | Group G | - |
Divisions
Division | Description |
1 | The substance referred to by class is continuously present or some of the time during normal conditions |
2 | The substance referred to by class is present only in abnormal conditions, such as a container failure or system breakdown. |
Markings
Example of product markings for US and Canada using Divisions:
Class I, Division 1, Group C, T4
Class I, (Flammable Gases or vapours), Division 1- Area Classification
Group C- Ethylene
T4- Temperature Code (See above). The American temperature codes are broadly similar to European
Example of product markings for US and Canada using Zones based on NEC505:
Class I, Zone 1, AEx de IIB T4
Class I, (Flammable Gases or vapours), Zone 1- Area Classification
AEx- Explosion proof in accordance with NEC 505
de- Protection method, Flameproof & Increased Safety components
IIB- Gas Group
T4- Temperature rating
Industry Bodies
Underwriters Laboratories (UL)
UL is a privately owned American company that tests to make sure that products meet safety standards
Mine Safety and Health Administration (MSHA)
The North American MSHA’s Approval and Certification Centre approves and certifies certain mining products for use in underground coal and gassy underground metal mines. The centre which is internationally recognized, tests equipment, instruments, and materials for compliance with Federal regulations. Products that pass testing are deemed MSHA approved or MSHA certified.
International Electrotechnical Commission (IEC)
The IEC was founded several years ago and consists of many countries including USA. Its purpose is to set up standards of explosion protection for electrical products and classification of areas. IECEx is an international certification scheme created by IEC to facilitate international trade in electrical equipment intended for use in explosive atmospheres. The emergence of the IECEx standard provides an opportunity to sell products in countries that do not accept the ATEX or UL standards.
IECEx is designed to eliminate the need for multiple national certifications by providing one international certificate and certification mark accepted by all participating countries.
The IECEx certificate of conformity attests that the products conform to the relevant IEC standards. The certificate is recognized by all participating countries as being equivalent to their own national certification. For more information on IECEx and details of the member bodies in each country please refer to www.iecex.com.
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