Intrinsically safe electrical apparatus are divided into 3 categories “ia” , “ib” and “ic”
Safety Level –ia- If a single fault or any combination of 2 faults occurs during normal operation, the electrical apparatus of this category must NOT be capable of causing an ignition
Safety Level –ib- This category must NOT be capable of causing an ignition during normal operation and with occurrence of a single fault Safety Level –ic- Limit the energy and spark during normal operation but suitable for zone 2 usage only