Hazardous area classification

What is hazardous area classification?

Hazardous area classification is the process of classifying areas where Explosive gas, dust or powder atmospheres may form.

  • Hazardous area meaning

While hazardous area is an area where there are chances of explosion due to explosive gas atmospheres. However, Every location has its own specific requirements. That depends upon the nature of present gases at the workplace atmosphere.

Hazardous area classification(Zones and division)

Basic components that cause explosion are Flammable materials, Oxygen, and an ignition source. The flammable material consists of gas, mists, and dust. While ignition source consists of heat source or spark etc. Whenever these three things are available in an area, The area will be considered as a hazardous area.

Two systems are in use for hazardous area classification. One is a class or division system and the other is a zone system. Class or division system is mostly operational in the US and Canada. However now these countries are moving toward a zone system. We will discuss both types.

Class or Division classification System

In this type of hazardous area, classification locations are classified into Class, Division, and Group. Where Class defines general nature properties of hazardous materials in the surrounding. We further divide it into class 1, 2 and 3.

Class I: this type of class include those Locations where vapors or flammable gases may or may not be the insufficient quantity to cause an explosion.

Class II: This type of class includes Locations where combustible dust may or may not be in sufficient quantity to cause an explosion.

Class III: this type includes Locations where ignitable fibers may or may not be in sufficient quantity to produce explosive or ignitable mixtures.

Division: We can define division as the probability of the hazardous material whether to cause an explosion or not. We also divide it further into Division1 and Division2.

Division 1: When there is a high probability of hazardous material to cause explosion or produce ignitable mixture in self-operating conditions.

Division 2:It can be defined as a hazardous material with a low probability to produce an explosive or ignitable mixture. Similarly, it exists for a short time period and during abnormal conditions.

 

Groups: The Group defines different types of hazardous material in the surrounding atmosphere. Further hazardous area classification can be carried out by different types. The different types of classes of Groups are below.

Class I: A, B, C, & D  For Gases Only

Class II or III: groups E, F,& G are for dust flying. The materials in each group are given below.

Group A: An area which contains acetylene.

Group B: An Atmospheres having a flammable material like gas, flammable or combustible liquid, or vapor whose MESG is less than 0.45 mm.

Group C: Atmospheres or areas containing a flammable gas, liquid, or vapor whose MESG is greater than 0.45 mm but less than or equal to 0.75 mm. Or MIC ratio greater than 0.40 and less than or equal to 0.80. Materiel likes ethylene either, acetaldehyde, and cyclosporine.

Group D: Atmospheres containing a flammable gas, liquid, or vapor whose MESG is greater than 0.45 mm but less than or equal to 0.75 mm. Or MIC ratio greater than 0.40 and less than or equal to 0.80. Materiel like acetone, benzene, butane, ethanol, gasoline, methane,propane, ammonia, etc.

Group E: This group include atmospheres that contain  combustible metal dust such as aluminum and magnesium.

 Group F: This group consists of combustible carbonaceous dust with an 8% volatility rate or more. Material like carbon black, coke dust, or coal is an example.

Group G: All those material or Atmospheres that are not covered by Group E or Group F Are called group G. Materials like starch, flour, Wood, Grain, plastic and other chemical comes in this category.

Hazardous area Zone classification

Zone is another system that is used for hazardous area classification. It is defined as the probability of sufficient hazardous material such as gas or dust, being to produce explosive or ignitable mixtures. Different zone exists for different materials. We are discussing here both gas and dust.

Zone 0 for gas: flammable gases, Vapor placed for a long time.

Zone 1 for gas: flammable gases, vapors in normal operating conditions.

Zone 3 for Gas: flammable gases or vapors that have less probability to occur. And for a short time duration.

Dust and powder

Different types of zones for dust are zone 20, zone 21, and zone 22.

Zone 20: This type of zone consists of ignitable powder or combustible dust for a long time in a specific place or area.

Zone 21: when ignitable materials or combustible dust occur under normal conditions.

Zone22: In this type of zone the probability of ignitable or combustible dust occurrence is low or for a short period of time.