Hazardous area classification

by Apr 10, 2019Machine Safety

When electrical equipment is used in an area characterized by a presence of flammable gases, liquids, fibers or dust, the risk of fire or explosion becomes more significant.

The places where this risk is to be taken into account are called hazardous or classified areas. The classification can be done using two systems, the class / division system and the zone system.

Previously, the system used in North America was the class / division system. Currently, the classification system has been changed to the zone system in order to harmonize the classification criteria with the rest of the world. However, the class / division system could still be used for existing equipment or facilities.

In the following article, a brief explanation of both systems will be presented:

  • The classes/divisions system

According to this system, areas are classified according to classes, divisions and groups.

The class of a hazardous area defines the nature or characteristics of the material likely to cause a fire or an explosion. There are three classes: Class I which includes areas with flammable gases or vapors, Class II for combustible dust sites and Class III for areas with flammable fibers.

Once the class of the site is defined, the division that reflects the probability of a fire or explosion being caused by the presence of the hazardous material (gas, vapor fibers, etc.) must be determined. For this level, classification is done according to two different divisions. Division 1 for areas with high probabilities of explosion or fire due to a permanent presence or intermittent periodic presence of the hazardous material or its presence inherent to an equipment itself. While division two represents areas with low probabilities of fire or explosion since hazardous materials are present under special conditions and for short periods of time.

Finally, the final criterion for classification of hazardous areas is the group, which is used to more specifically determine hazardous materials in the equipment environment.

There are seven hazardous areas groups from group A to group F. Groups A to D are for gases, while groups E, F and G are for dust and volatiles. At this level, the correspondence between the different levels of classification begins to appear (ex: Group from A to D are connected to class I only, groups E, F and G are connected to classes II and III).

  • The zone system

For this system, it is necessary to start by determining the type of material present, gases or dust, and depending on the material, it is necessary to define the zone according to the probability that the concentration or the quantity of the dangerous material is sufficient to cause an explosion or a fire.

For gases, there are two types of zones. Zone 0 for a permanent presence of a hazardous material that is in sufficient concentration to cause a fire or explosion. Zone 1, meanwhile, represent the places where a sufficient concentration of hazardous materials could possibly be present under normal operating conditions.

For dust, the zones are divided into three levels according to the probability of occurrence of a fire or explosion depending on the concentration and the duration of presence of the concentration of the hazardous material in the equipment environment. The probability decreases from zone 20 to zone 22 passing through zone 21.

For this system, another classification criterion is added. This is the classification of equipment into three groups. Groups in this system specify only the characteristics of the equipment and not the nature of the hazardous materials as defined in the class / division system.

The grouping of equipment is based on the explosive nature of the place where they will be exploited (Maximum Experimental Safe Gap—MESG as the main criterion).

The other criterion to be taken into consideration and which depends on the equipment itself is that of the temperature (T), which determines the maximum temperature that the surface of an equipment cannot exceed if it is operated in an ambient temperature.

This article has been dedicated mainly to a simple explanation of the classification systems of hazardous areas, another blog will be published concerning the interpretation of the symbols that serve to verify the correspondence between an equipment and the characteristics of the zone where it will be exploited.

Questions or comments?

Intervention Prévention Inc.

Intervention Prévention œuvre dans le domaine de la sécurité au travail en offrant des services spécialisés répondant aux normes CSA Z462 – Sécurité électrique en milieu de travail, CSA Z460 – Maîtrise des énergies dangereuses : Cadenassage et autres méthodes, et CSA Z432 – Protection des machines. Nos domaines d’expertise sont donc reliés au cadenassage, à la sécurité électrique et à la sécurité machine. La satisfaction de nos clients est le gage de notre compétence


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