Posted By Innes Gray The basis for intrinsic safety as the type of protection is that a certain minimum igniting energy is required to ignite an explosive atmosphere IA intrinsic safety In an intrinsically safe circuit, this minimum igniting energy does not exist in the Hazardous area in normal operation or in a malfunction. The intrinsic safety of a circuit is achieved by limiting the current and voltage. The intrinsic safety”I” type of protection is therefore restricted to circuits with relatively low power levels. In an intrinsically safe circuit, therefore, there are no Sparks or Thermal effects (temperature raises) during operation or a malfunction which could cause ignition of an explosive atmosphere. XA Are Sealed units where we know there will be explosive atmosphere and the source will have Sparks or Thermal effects This may explain the what is and is not where they can be used that is another story