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An explosion hazard occurs in the industry, warehouse which stores. processes and manufactures inflammable such as:gas, liquid, solid. A mixture of inflammable substancce in the form of gas, vapours, mist or dust with air we call an Explosive Atmosphere.
Explosion rises if in the Explosion Atmoshere – excessive temperature, an electrical arc, spark or any other energy ignition occurs. The equipment for EX zones – due to ATEX directives – is divided into Groups and Sub-groups:
LIST OF EQUIPMENT FOR EX W/G ZONE DIRECTIVE ATEX
I – the equipment for alla underground coal with firedamp
II – the equipment for hazardous areas other than undeground coal mining
SUB-GROUPS OF INFLAMMABLE DUST AND VARPOUS EXPLOSIVENESS FOR GROUP II
IIA – Propane group (for example.: acetone, ethyl and methyl alcohol)
IIB – Ethylene group (for example: ethylene, hydrogen sulphide)
IIC – Hydrogen group (acetylene, hydrogen, carbon disulphide)
The self- ignite temperature or spontaneous igniton temperature is the minimum temperature at which an explosive atmosphere can spontaneisly ignite.
The energy required to start a flame can be changed to themal form by an increase in the temperature of the mixture. The explosive mixtures are allocated into broad bands giving the Temperasture Class meaning the maximum surface temperatures for the electrical equipment.
Temperature class – maximum temperature for increasing of equipment surface
| Temp.class | Max surface temp. | Self-ignition temp. |
|---|---|---|
| T1 | 450oC | 450oC |
| T2 | 300oC | > 300oC |
| T3 | 200oC | > 200oC |
| T4 | 135oC | > 135oC |
| T5 | 100oC | > 100oC |
| T6 | 85oC | > 85oC |
The explosion hazardous areas are divided into Zones.
| Explosive Atmoshere | Explosion Hazardous Zones | |
|---|---|---|
| a mixture of air with: gas, varpours, mist or inflammable dust G | ZONE O | an area in which an explosive atmosphere is continously present or for long periods or frquently |
| ZONE 1 | an area in which an explosive atosphere is likely to occur occasionally in normal operation | |
| ZONE 2 | an area in which an explosive atmoshere is not likely to occurr in normal operation but if it does occur, will persist for a short period only |
| Explosive Atmoshere | Explosion Hazardous Zones | |
|---|---|---|
| a mixture of air with: inflammable dust D | ZONE 20 | an area in which an explosive atmosphere is continously present or for long periods or frquently |
| ZONE 21 | an area in which an explosive atosphere is likely to occur occasionally in normal operation | |
| ZONE 22 | an area in which an explosive atmoshere is not likely to occurr in normal operation but if it does occur, will persist for a short period only |
EXPLOSION-PROOF ENCLOUSERS ARE DIVIDED INTO THE PROTECTION SUB-GROUPS.BELOW WE PRESENT SOME EXAMPLES OF PROTECTION SUB-GROUP:
„e“ increased safty protection – normally sparking components are excluded from this method of protection. Other components are designed to substsntially reduce the likelihood of the occurance of fault conditions which could cause ignition. This is done by reducing and controlling working temperatures, ensuring the electrical connections are reliable, increasing insulation effectivness and reducing the probability of contamination by dirtt and moisture ingress.
„d” flameproof enclosure protection – the pontentially incendive parts are contained within an enlosure into which the explosive atmosphere can enter but which will contain. Any resultant explosion and prevent its transmission outsider of the enclosure.
„n” non speaking protection – for this method precautions are taken with connection and wiring to increase reliability, though not as high degree as for Ex e. Where internal surfaces are hotter than the desired T rating, they can be tightly enclosed to prevent the ready ingress of an explosive atmosphere.