DUST Groups

Electrical Equipment for Group III (DUST)

Electrical Equipment for use in explosive Atmospheres are divided according to the following types of explosive atmospheres (To facilitate the procedure of selection of equipment)

The (historic) Explosive Atmosphere in the MINES (Below-surface).  The atmosphere inside the mines may consist of explosive gas/vapours or explosive dust or a combination of these.

Electrical equipment for use in mines are referred to as GROUP I Electrical Equipment.

Equipment protection Levels are:-

Ma

Mb

The Explosive Atmosphere which is formed due to gases & vapours and is above-surface (not in the Mines).

The Electrical Equipment for use in this atmosphere are referred to as Electrical Equipment of GROUP II

This atmosphere is formed due to Explosive Gases and due to large number of explosive gases involved , the classification is further divided into following GAS GROUPS:-

II  A      (a well-known industrial gas : PROPANE)

II  B      (a well-known industrial gas : ETHYLENE)

II C      ( well-known industrial gases HYDROGEN , CARBON DISULPHIDE)

(It is evident that the gases have been grouped according to the chemical & physical properties)

The Explosive Atmosphere which is formed due to DUST & FLYINGS (fiber or fluff  as cotton, or wooden flyings ) and is above-surface (not in the Mines).

The Electrical Equipment for use in this atmosphere are referred to as Electrical Equipment of GROUP III

This atmosphere is formed due to Explosive DUST and due to large number of types of explosive DUST & FLYINGS involved , the classification is further divided into following DUST GROUPS:-

III  A     Combustible Flyings

III  B     Combustible but non-conductive Dust (The particle size of the dust grain is 500 micro meter or less, and can remain suspended  in air and may settle due to its own weight)

III C     Combustible & conductive Dust (The particle size of the dust grain is 500 micro meter or less, and can remain suspended  in air and may settle due to its own weight)