Equipment Grouping

In an explosive atmosphere, only suitable equipment must be installed: suitable means that they cannot ignite the explosive atmosphere. There are 3 types of Explosive atmospheres:

• The one present in mines: the gas is called Firedump.
• Explosive Gas Atmosphere: for example, the one inside a gas pressure reduction box
• Explosive Dust Atmosphere: for example, inside a woodworking factory

For that reason, equipment for explosive atmospheres are divided into three groups:

Equipment of Group I is intended for use in mines susceptible to firedamp. Equipment intended for mines where the atmosphere, in addition to firedamp, may contain significant proportions of other flammable gases (i.e. other than methane), shall be constructed and tested in accordance with the requirements relating to Group I and also to the subdivision of Group II corresponding to the other significant flammable gases.

Firedamp is a mixture of flammable gases, consisting primarily of methane (CH₄), that occurs naturally in coal seams and sometimes in ore mines. It is particularly dangerous in underground mines because it can accumulate in pockets, causing explosions if it comes into contact with a spark or heat source.

Main characteristics:

• Composition: Mainly methane, but may also contain other gases in minimal quantities.
• Colorless and odorless: In pure form, firedamp is difficult to detect without specific instruments.
• Density: It is less dense than air, so it tends to accumulate in elevated or poorly ventilated areas of tunnels.
• Explosive limits: It is explosive at concentrations between 5% and 15% in air

Equipment of Group II is intended for use in areas with an explosive gas atmosphere other than mines susceptible to firedamp.

Equipment of Group II is subdivided according to the nature of the explosive gas atmosphere for which it is intended.

Group II subdivisions:

•  IIA, a typical gas is propane
•  IIB, a typical gas is ethylene
•  IIC, typical gases are hydrogen and acetylene

This subdivision is based on the maximum experimental safe gap (MESG) or the minimum igniting current ratio (MIC ratio) of the explosive gas atmosphere in which the equipment may be installed.

Please bear in mind that Equipment marked IIB is suitable for applications requiring Group IIA equipment. Similarly, equipment marked IIC is suitable for applications requiring Group IIA or Group IIB equipment.

Equipment of Group III is intended for use in areas with an explosive dust atmosphere other than mines susceptible to firedamp.

Equipment of Group III is subdivided according to the nature of the explosive dust atmosphere for which it is intended. Group III subdivisions:

• IIIA: combustible flyings
• IIIB: non-conductive dust
• IIIC: conductive dust

Please bear in mind that Equipment marked IIIB is suitable for applications requiring Group IIIA equipment. Similarly, equipment marked IIIC is suitable for applications requiring Group IIIA or Group IIIB equipment.

Ex db I Mb

Electrical equipment with Type of Protection flameproof enclosure “d” (EPL Mb) for use in mines susceptible to firedamp.

Ex db [ia Ga] IIC Gb

DEF 02.0536 U

Ex Component (please notice the letter “U”), with Type of Protection flameproof enclosure “d” (EPL Gb) with intrinsically safe “ia” (EPL Ga) output circuit, for explosive gas of subdivision C.

Ex eb pxb IIC 125 °C (T4) Gb

GHI 02.0076 X

Electrical Equipment, utilizing types of protection increased safety “e” (EPL Gb) and pressurized enclosure “px” (EPL Gb), maximum surface temperature of 125 °C, for explosive gas of subdivision C, with gas of ignition temperature greater than 125 °C and with specific conditions of use indicated in the certificate (please notice the letter “X”).