Talking gas #5: Explosion safety standards and certifications for gas detection detectors

The likely area in which a mixture of flammable gas, vapor, dust and air is likely to occur is called ‘hazardous-hazardous’, and other areas are ‘safe-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 faulty condition, it cannot initiate an explosion.

Gas Measuring Equipment Crowcon meets all European, American and other international standards for electrical equipment used in hazardous areas.

European Approval Certificate


  • CENELEC is the European Commission standardization for electrical engineering. It was officially recognized as the European Organization in its field by the European Commission in Directive 83/189 EEC. CENELEC uses IEC (International Electro-Engineering Commission) standards for reference and harmonies them with all European Community countries (see below)

ATEX Directive

  • ATEX, (derived from Atmosphere Explosif) is the name given to the frameworks for fire control and the standards of the equipment and protection systems used in it. ATEX includes the Directive and is an extension of CENELEC standards. It refers to problems that were not solved by the original EN standards such as dust hazards. That brings about common standards that should completely eliminate trade barriers in the European Community.
  • ATEX requires employers to remove or control risks from hazardous substances. Field operations operations must ensure that factories, equipment, protection systems and related connection devices are put into service if explosion-fighting materials specify that they can be safely used in a fire-fired environment , including gas detectors of all kinds. ATEX is based on the requirements of the two European markets.
  • Directive 99/92/EC (also known as ‘ATEX 137’ or ‘ATEX Workplace Directive’) on minimum requirements for improving the health and safety of potentially at-risk workers from fire and explosion.
  • Directive 94/9/EC (also known as ‘ATEX 95’ or ‘the ATEX Equipment Directive) on estimated laws of Member State regarding equipment and design protection systems for use in explosive environments. Directive 94/9/EC divides the protective devices and systems it includes into groups of equipment types; This directive provides for a classification by the employer in places where fire and explosion can occur under the individual conditions of the area, identifying the group of equipment and protection systems that should be used in each zone. See below.

Classification of hazardous areas

  • Dangerous places are classified based on the conditions of the above regions on the basis of the frequency and duration of the appearance of an explosive atmosphere.
  • Areas with flammable gas hazards are classified as Zone 0, Zone 1, or Zone 2.
  • Areas that limit the risk of flammable dust are classified as possible Zone 20, Zone 21 or Zone 22.
  • Note: Flammable layers, deposits and heap dust must be treated as any other source that can form an explosive atmosphere.
  • A description of each Zone is displayed on the page table below.

Classification of devices in combination with ATEX Directive

  • ATEX Directive defines 2 groups of devices
  • Group 1, the device is designed for use in mining applications, divided into M1 and M2 types. The M1 determines that the device must continue to operate when potentially explosive is present. The M2 determines the device does not work when an explosive device is present.Handheld gas detects will be listed in this classification
  • Group 2 is for all other surface industries. and divided into types 1, 2 and 3. Type 1 equipment is designed for use in Zone 0 environments. Type 2 devices are designed for use in Zone 1 environments. Type 3 devices are designed for use in Zone 2 environments.
  • This condition is mandatory for manufacturers if they produce equipment of use in type 1, 2, M1 and M2.
1 An area where an explosive atmosphere consists of a mixture with air or flammable substances in the form of gas, dew or dust that appears continuously or for long periods of time or frequently. Gas: Zone 0


Dust: Zone 20

2 An area where there is an explosive atmosphere consists of a mixture with air or flammable substances in the form of gas, mist or dust that may occur during normal operation from time to time. Gas: Zone 1


Dust: Zone 21

3 An area where there is an explosive atmosphere consists of a mixture with air or flammable substances in the form of gases, dew or dust is unlikely to occur during normal operation, but if it occurs, it will only last for a short time. Gas: Zone 2


Dust: Zone 22

Explosion proof:

In equipment design, various protective techniques are used to prevent explosions. Examples are given in the table below.




Safe version “ia” or “ib” Energy limits of sparks and temperatures. This includes one (b) or two (a) electrical problems that may raise the surface temperature above the value “T”. Ex ia


Ex ib










Special “s” Any method can be proven to be safe. Ex s 0,1,2 1,2,3 2
Fire prevention “d” Filling powder/sand “q” Including explosion prevention and fire prevention Ex d


Ex q










Enhanced safety “e” Do not ignite “n” No arc launch, no hot surface, no power release by moisture restrictions Ex e


Ex n










Pressure “p” Pump inert gas continuously or stabilize pressure so as not to let flammable gases penetrate hot surfaces or fire sources Ex p 1,2 2,3 1,2
Cover “m” Wrapping electrical components with plastic Ex m 1,2 2,3 2

Temperature classification

To ensure that there is no risk of fire due to hot surfaces, the device is classified in relation to the maximum surface temperature of any part of the device during work or due to an error that when the ambient temperature is around 40°C. This is known as the value “T”. The device must be selected with the appropriate temperature classification that it when the maximum surface temperature does not exceed the ignition temperature of the gases and vapors where those will be installed.

Gas group, equipment group and temperature range

Gas is grouped together based on the total energy required to ignite the explosive gas mixture with air. The device is classified into groups according to the gases and vapors that it fits.

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

Markup noting

  • The ATEX directive requires the certified product to be marked with the CE mark (confirming compliance with the required EMC and Low Voltage Directive regulations for the device containing the voltage source), the ‘EX’ mark (in which the device is designed for use in a hazardous area) and the device code (group confirmation , the gas group and the temperature classification at which the products are certified). We can see an example on the back of any handheld gas detector.
  • ATEX Group and Category
ATEX detonation sign
ATEX detonation sign

Product label example

Example of an explosion prevention sign on the back of a handheld gas detector
Example of an explosion prevention sign on the back of a handheld gas detector
  • Note: Tamb (Ta) in which the ambient temperature range of which the products are certified (i.e. will not cause ignition); it does not specify the operating temperature of the product.
  • The latest standards introduce a ‘Protection Level’ to certification of secure encryption structures. An example of a certification number shows the following level of protection:
railway station Zone 0 Gas
gb Zone 1
Gc Zone 2
skin Zone 20 Dust
Db Zone 21
dc Zone 22

Approval agency

  • There are many official agencies that recognize product testing and quality inspection procedures to verify that the product complies with the requirements of mandatory directives such as ATEX. For services related to ATEX and IECEX approvals, Crowcon uses Baseefa, Sira and UL/DEMKO.
  • For services related to North American approval, Crowcon uses UL (Underwriters Laboratories), and CSA (Canadian Standards Association)

North American Approval – North American

  • As a result of North America, Canada and Europe are aiming for the harmony of the National Electricity Code (NEC) and the Canadian Electricity Rule (IEC) which now recognize the use of European Zone systems for classification of hazardous areas. Article 505 of the NEC basically created an Americanized version of the International Electro-Engineering Commission (IEC, see below) and cenelec’s Zone system. Nec 505 is not the same, but it is suitable for European IEC Zones while maintaining NEC protection techniques. In North America, hazardous areas are divided by layers, units, regions, and groups to determine the level of safety for equipment installed at locations. The layer determines the general form of flammable materials in the atmosphere. The unit determines the probability of the presence of flammable materials. The region determines the location as in Europe and accurately group the flammable substances of the material.


1 – Gas and steam Flammable or vapor gases are present in the air in sufficient quantities to form explosive or flammable mixtures.
2 – Dust Presence of flammable and conducted dusts
3 – Fibres and Materials Flammable fibers and materials that produce flammable components are present, but are not capable of floating in sufficient quantities to create flammable mixtures. (This Group Classification does not apply to these classes)

Regional classification

The processing plant is divided into Regions (European and IEC methods) or Units (North American methods) according to the possibility of explosive presence.

Units and Regions

Zone 0 – Gas


Zone 20 – Dust

An area where an explosive mixture is constantly present or present for long periods of time. Class I Division 1 (Gas)


Class II Division 1 (Dust)

Zone 1 – Gas


Zone 21 – Dust

An area where an explosive mixture can occur during normal operation. Class I Division 1 (Gas)


Class II Division 1 (Dust)

Zone 2 – Gas


Zone 22 – Dust

An area where a mixture explodes is unlikely to occur during normal operation and if it happens, it will only survive for a short time. Class I Division 2 (Gas)


Class II Division 2 (Dust)

Gas and dust group

Acetylene A 11C
Hydrogen B 11C
Ethylene C 11B
Propane D 11A
Methane D
Metal Dust e
Coal Dust f
Grain Dust G


Division depict
1 Class reference substances are constantly present or a few times under normal conditions.
2 Class reference substances are only present under abnormal conditions such as system crashes or problems


  • Examples of product markings for the U.S. and Canada
  • 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 Agency

Underwriters Laboratories (UL)

  • UL is an American privately owned company that can test to ensure that the products meet safety standards

Mine Safety and Health Management (MSHA)

  • Msha North American Center for Approval and Certification will certification of certain mining products for use in underground coal and gas metal mines. Internationally recognized centers, testing equipment, tools, materials to constability with federal regulations. Products that pass testing are considered MSHA approval or MSHA certification.

International Electro-Engineering Commission (IEC)

  • IEC was founded a few years ago and includes many countries including the US. Its purpose is to establish explosion-resistant standards for electrical products and regional classification.
  • IECEX is an international certification model created by IEC to facilitate international trade in electrical equipment for use in explosive environments. The appearance of IECEX standards provides an opportunity to sell products in countries that do not accept ATEX or UL standards.
  • IECEX is designed to eliminate the need for multiple national certifications by providing an international trademark certificate and certification accepted by all participating countries.
  • The IECEX Conformity Certificate proves that the products consed with the relevant IEC standards. Certificates recognized by all participating countries are equivalent to their own national certificates. For more information about IECEX and details about member organizations in each country please refer to www.iecex.com.


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