The standard of electrical installations and equipment in explosives buildings is determined according to the explosive hazard which is likely to be encountered, such as the quantity and nature of the explosives present and the atmospheres that may occur during the processes undertaken.
There are 4 broad standards or categories of electrical installation which are denoted by the letters A, B, C and D, which are selected based on standard algorithm. The Dangerous Substances and Explosive Atmospheres Regulations are concerned with protection against risks from fire, explosion and similar events arising from dangerous substances used or present in the workplace. They set minimum requirements for the protection of workers from fire and explosion risks related to dangerous substances and potentially explosive atmospheres. Classification of zones is a process of detailed analysis of the potential for release of explosives dust or vapor; it is not a straightforward empirical process.
Category A – Zone Determination
Cat A areas are sub divided into three zones, Zone 0, 1 and 2 recognize the differing degrees with which explosive concentrations of gases/ mists/vapors may arise in terms of both the frequency of occurrence and the probable duration of existence on each occasion.
Zone 0 “A place in which an explosive atmosphere consisting of a mixture with air or dangerous substances in the form of gas, vapor or mist is present continuously or for long periods frequently.”
Zone 1 “A place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapor or mist is likely to occur in normal operation occasionally.”
Zone 2 “A place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapor or mist is not likely to occur in normal operation but, if it does occur, will persist for a short period only.”
Category B – Zone Determination
Cat B areas are sub divided into three zones, as below,
Zone 20 “A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is present continuously, or for long periods or frequently”
Zone 21 “A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur in normal operation occasionally”
Zone 22 “A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is not likely to occur in normal operation but, if it does occur, will persist for a short period only”
Category C & D Electrical Installations
Category C electrical installations are required for explosives buildings where the explosives and the activity within do not give rise to flammable vapor or explosive dust atmosphere or give rise to an explosive hazard due to accumulated dust.
Category D comprises buildings, rooms, etc. where authorized small quantities of explosives, except HD 1.1, are stored or processed as determined by the departmental IE, and in which explosives are not exposed, and activities do not give rise to flammable vapor or explosives dust.
