International Electrotechnical Commission (IEC) has developed the standard IEC60079-0:2004 (Electrical apparatus for explosive gas atmospheres Part 0: General requirements) Which provides directives of electrical safety in hazardous areas. The directive divides potentially explosive gases into two groups: Group I relates to mines susceptible to fire damp (methane) and Group II relates to other places.

Overview

Flour mills, bakeries, sugar processors, timber processors, coal handling plant, paper mills and processors of metals such as aluminum and magnesium, for example, can all have areas where dust-laden atmospheres are potentially explosive, so it can be seen that the full spectrum of production and process plants that can contain hazardous areas is extremely broad.

Hazardous Location Types - Zones

Zone 0

An area in which an explosive gas-air mixture is continuously present or present for long periods.

Zone 1

An area in which an explosive gas-air mixture is likely to occur during normal operation.

Zone 2

An area in which an explosive gas-air mixture is unlikely. If it does, it is only for a short period of time.

Zone 10

An explosive atmosphere, resulting from dust which is present continuously or for long periods of time.

Zone 11

A short-lived explosive dust atmosphere from unsettled dust deposits.

Hazardous Location Gases - Groups

IEC directives divide potentially explosive gases into two groups: Group I relates to mines susceptible to fire damp (methane) and Group II relates to other places.

Group II is further subdivided into three to reflect the different flammability of gases (and vapors and mists). Group IIA is for the least flammable gases (such as propane), while Group IIB is for medium-flammability gases (such as ethylene) and Group IIC is for the most flammable (such as hydrogen). However, it should be remembered that, in general, gases on their own are not flammable; they also need oxygen or another oxidant with which they can react in combustion. The exception to this rule is acetylene, which can decompose explosively in the absence of oxygen into carbon and hydrogen.

Specifiers gas detection equipment for hazardous areas need to know the likelihood of the explosive gas-air mixture being present and select only equipment approved for the specific hazardous area location.