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Special Cases

Category 3 devices

In contrast to Category 1 and 2 devices,potential hazards in the event of failure (e.g. short circuiting, connection break etc.) do not have to be considered for Category 3 devices (for use only in Zones 2 respectively 22). The device is evaluated only in respect of hazards during normal operation. It is relatively unlikely that the device should fail at the same time as a short-term explosive atmosphere is present. No EC Type Approval Test Certificate is therefore required for Category 3 operating devices. The manufacturer may confirm that the operating device complies with the relevant standard. None the less, ecom Category 3 devices are still tested by a certified centre and ecom is then awarded a declaration of conformity.

 

  • Of course, Category 2 operating devicesalso offer significantly greater safety in Zones 2 respectively 22
  • Dust explosions - albeit of a predominantlyminor nature - occur relatively frequently.

A leaflet issued by the Government Safety Organisation of the Federal Republic of Germany states:

"According to documentation published by property insurers, it can be assumed that an average of one dust explosion per day occurs in the Federal Republic of Germany; around one in four of these explosions are caused by food stuff or animal feed dusts."

Dust explosions are a world-wide problem. Between 1980 and 1990 in the USA, for example, some 200 serious food stuff or animal feed related dust explosions were recorded, causing 54 deaths, 256 injuries and property damage amounting to 165million US dollars.

 

Electrical operating devices represent only a small proportion ofthe ignition sources found to cause dust explosions – not least due to thesafety stipulations in the regulations for erecting electrical plants inpotentially-explosive areas.

 

With the introduction of the alreadyoutdated "Regulation on electrical equipment in explosive areas,ElexV" [1.4] in 1980, a type approval test certificate by a prescribednominated body was legally required for electrical equipment intended for usein zone 10 (in zones 20 and 21 from 01/07/2003).

 

”Dust explosion-protected” operatingdevices, the surface temperatures of which lies below the acceptable limit forstandardised dust thickness of 5mm, can, despite the existence of an officialtest certificate, become a danger source if, contrary to the conditions, theybecome covered or completely encased with a thick layer of dust.