Explosive atmospheres and their risks. How can we approach them?

Refineries are typical zones with explosive atmospheres

Explosive atmospheres and their risks. How can we approach them? 

Workplace accidents remain one of the main challenges faced by some industries. There is, in fact, a direct relationship between the accident rate and the tools used. However, most companies and workers still do not know how to work safely, and what tools need to be used in hazardous environments.

Speaking of hazardous environments, today we come to know what explosive atmospheres (ATEX) are, and how to perform in them.

What are explosive atmospheres? 

To get straight to the point, an explosive atmosphere is a mixture of flammable substances (whether in the form of gas, vapor, mist or dust) with air that, after ignition, lead to a combustion that spreads to the entire unburned mixture.

However, explosive atmospheres are not flammable per se, conditions must be met. In other words, there must be an enough mixture of air and flammable substance. Therefore, for this substance to give rise to an explosive atmosphere, it needs to have a minimum and maximum percentage of air (oxygen) that, otherwise, would not lead to a combustion, and therefore would not be considered an explosive atmosphere.

And liquids? 

Although we have said that an explosive atmosphere is the mixture of a flammable substance, either in the form of gas, vapor, mist or dust, it does not mean that liquids are not out of this risk. Liquids are not, in themselves, explosive atmospheres, but they do generate vapors on their surface that, if they mix with air, then they can give rise to an explosive atmosphere.

Not all gas or dust have the same qualities 

Depending on these qualities, there is a different ignition limit. In fact, gases are classified into four main groups, based on ignition temperature:

  • I such as methane gas
  • IIA (Acetone, benzene, gasoline): They have an ignition energy higher than 0.18 mJ
  • IIB (Coal gas): They have an ignition energy of between 0.06 and 0.18 mJ
  • IIC (Hydrogen, acetylene): They have an ignition energy less than 0.06 mJ

Download our whitepaper to learn more

Obviously, gases with the lowest ignition limit are the most dangerous ones, since the probability of a spark reaching the ignition limit is higher.

What directives regulate explosive atmospheres? 

Many governments have developed legislations and standards that make it possible to improve conditions in the workplace. The European Union has led this initiative by implementing Directive 1999/92 / EC on ATEX, which defines the requirements to work safely in hazardous environments.

What does this regulation say about explosive atmospheres? 

First, the EN 1127 standard, cited in the Directive, defines 3 different zones depending on the degree of risk of the explosive atmosphere:

  •  Zone 0/20: Danger is always present, for a long time or frequently (more than 1000 hours per year)
  •  Zone 1/21:  Danger is occasionally present (between 10 and 1000 hours per year)
  •  Zone 2/22: Danger is seldom present or present for a short time (between 0.1 and 10 hours per year)

On the other hand, this standard indicates that tools, in general, are a source of ignition (mainly the ones made of steel) and, as we have seen before, there are explosive atmospheres where, depending on the type of gas, a small spark can suddenly become the perfect imitation of hell.

That is, depending on which areas, there is a prohibition or limitation on the use of tools or of their types, namely:

  • Zones 0 (gas) and 20 (dust): No tool that could generate sparks can be used (not only the one made of steel).
  • Zones 1 and 2 (gas): It can be used tools made of steel of:
    • Type A: They do not generate sparks in their regular use such as wrenches or screwdrivers
    • Type B: Only if it can be guaranteed that no explosive atmosphere exists at the workplace
    • With Group IIC gas or hydrogen sulfide, ethylene oxide or carbon monoxide, no steel tools are allowed.
  • Zones 21 and 22 (dust):
    • Tools made of steel of type A are allowed
    • The ones of type B can be used only if there is shielding between the workplace and the explosive atmosphere
      • Dust deposits should also be removed, keeping the workplace humid enough to ensure that such deposits do not lift.

So, what kind of measures do we take in ATEX zones? 

Above all, Directive 1999/92 / EC on ATEX states that all sources of ignition must be avoided, and if not possible, eliminate them completely, reduce them.

If they cannot be eliminated, then measures must be taken to mitigate the effects of the possible deflagration should it occur. The situation of a complete elimination cannot always be reached, since, today, industry and society in general have a need to use means that can be the reason for an ignition in an explosive atmosphere:

  • Machines
  • Electronics devices
  • Clothing
  • Mechanical tools

This does not exempt companies and their workers from acting. According to Directive 1999/92 / EC on ATEX, it is mandatory, first, to check if there is an explosive atmosphere or not, but even so, it is important to emphasize that said ATEX legislation indicates that all safety measures must be complied with, regardless of whether or not there is an explosive atmosphere at that particular time.

And if it is a classified area, all means must be put in place to avoid or reduce the sources of ignition and mitigate the consequences of a deflagration.

What tool to use, then, in explosive atmospheres?