Explosive environments: the ATEX standard
1. Source of combustion (flame, spark, hot spot)
2. Oxygen in the air
3. Fuel (gas or flammable vapor, dust)
Under what conditions can an explosion occur?
There is a risk of explosion when several elements are present:
- an oxidant: the oxygen in air, for example
- a fuel:
- gas or vapors: hydrocarbons, solvents, varnishes, diluents, gas, alcohol, dyes, perfumes, chemical products, agents for manufacture of plastics...
- powders and dust: magnesium, aluminum, sulfur, cellulose, cereals, carbon, wood, milk, resins, sugars, starch, polystyrenes, fertilizer...
- a hot spot or a source of combustion.
For example, when filling a grain silo, the concentration of dust is very high. The environment then is dangerous: a rise in temperature, or even a spark, can trigger an explosion.
If a risk of explosion is identified in an environment (gas or dust), a safety requirement is imposed for the use of equipment that is specifically designed to function without becoming a potential source of combustion. This equipment offers different types of protection designed to diminish the risk of explosion.
The ATEX standard
What is the ATEX?
The ATEX regulation is a European directive which requires all heads of organizations to fully understand the risks related to certain explosive environments. To do this, an evaluation of the risk of explosion in a company is required in order to identify any locations where explosive environments could form, and then to put in place the means to avoid explosion.
How do you choose equipment that is adapted for an environment at risk of explosion?
ATEX environments are subdivided into three zones:
- zones 0, 1 or 2 for gases
- zones 20, 21 or 22 for dust
There are two groups of materials:
- group I: concerns mines (more restrictive)
- group II: concerns all above-ground industries
For Group II (above-ground industries), a specifically adapted category of equipment is associated with each ATEX zone classification.
|Zone classification||ATEX classification required for equipment
(for Group II, above-ground industry)
Zone 0 (gas)
VERY HIGH LEVEL OF PROTECTION
The explosive mix is present constantly or for a long period of time
Zone 1 (gas)
HIGH LEVEL OF PROTECTION
An explosive mix may form under normal working conditions.
Zone 2 (gas)
NORMAL LEVEL OF PROTECTION
An explosive mix has a small chance of forming and would exist only for a short period.
What are the specific features of certified headlamps?
Products classified into different groups may have different modes of protection against explosion. These modes are designed for the zone in which the equipment is to be used. For example: zones 1/21, zones 2/22.
The more restrictive the mode of protection (zones 1/21, zones 0/20) is for a headlamp, the less powerful the lighting will be. The intensity and voltage that is permitted may be low in order to ensure that the device does not produce an arc, spark or dangerous temperature.
How are the gases classified?
The ATEX standard also has a classification for explosive gases against which the user can protect himself by using a product that has adapted protection.
For Group II materials, the danger of gases covered by a product grows from subdivision IIA, the least dangerous, to subdivision IIC, the most dangerous.
Some reference gases:
- group I: methane
- group IIA: propane
- group IIB: ethylene
- group IIC: hydrogen/acetylene
To determine by site type the gases that may be present and their subdivisions, consult the table of subdivisions for group II gases and vapors (surface installation).
Temperature classes for gases and dust
The exterior of a headlamp for use in hazardous locations must not present an external surface temperature that could provoke combustion. Different substances may combust at different temperatures. The lower the combustion temperature is, the more dangerous the substance is. Therefore, each piece of equipment used in an explosive environment is classified according to the maximal surface temperature it generates.
There are six classes of temperatures, from T1 to T6.
The maximum surface temperature of the equipment should always be well below the autoignition temperature of the dusts or gases present.
Autoignition classes and temperatures for gases
Hydrogen 560° (T1)
Methane 537° (T1)
Ethylene 425° (T2)
Acetylene 305° (T2)
Kerosene 210° (T3)
Ethyl ether 160° (T4)
Carbon disulphide 95° (T6)
Autoignition classes and temperatures for suspended dust particles
Soot 810° (T1)
PVC 700° (T1)
Aluminum 590° (T1)
Corn dust 510° (T1)
Sugar 490° (T1)
Flour 490° (T1)
Methyl cellulose 420° (T2)
Polyethylene 420° (T2)
Carbon dust 380° (T2)
Consult the classification of gases according to their autoignition temperatures.
To determine by site type the dusts that may be present and their autoignition temperature, consult the dust classification table (classified by autoignition temperature).
What does the marking mean?
All products designed for use in explosive zones have a specific marking on them. This marking contains all the information necessary to determine the zones in which the product may be used.
Example of marking:
CE 0081 II 2 GD Ex nAnL IIB T4
- CE: the equipment meets European standards for this product
- 0081: identification number of the notified body, when it intervenes in the inspection phase of production Here the number corresponds to the LCIE – Bureau Véritas. This number may also be 0080, for example for INERIS.
- : Use authorized for explosive environments
- II: equipment group
(I = mines, II = above-ground industry)
- 2 : category of equipment
(1 = permanent risk (zones 0/20), 2 = frequent risk (zones 1/21), 3 = occasional risk (zones 2/22))
- GD: type of fuel source: G = gases and vapors, D = dust
- Ex: the product meets the Cenelec protection standards
- nAnL: type of protection
- IIB: indicates the class of gases covered by the product
- T4: temperature class corresponding to a surface temperature