Ex i EN 60079-11 Explosive atmospheres. Equipment protection by intrinsic safety "i"
Based on the concept of removing the ignition source by reducing the power in the circuit i.e. keeping voltage and current below the ignition level of the hazard it is the 'safest' form of protection.1
With one exception2 Intrinsic Safety is the method used for Category 1G i.e. Zone 0.
A circuit in which any spark or any thermal effect produced in the conditions specified in IEC 60079‑11, including normal operation and specified fault conditions, are not capable of causing ignition of a given explosive gas atmosphere.
Unlike all other protection methods, for installed systems intrinsic safety is a system concept, not just an individual entity but a combination of interconnected entities.
Assuming a device is not self-contained i.e. portable then there will be at least two items (plus cable) to form an intrinsically safe circuit commonly referred to as a IS loop.
Each item in the loop can be one of 4 types:
| Associated Apparatus | Simple Apparatus | Certified Equipment | Cables | |
|---|---|---|---|---|
| Contains both IS and Non-IS circuits | Basic 2 terminal devices e.g. switches | Certified equipment | Connecting Cables |
As Intrinsic Safety is a system concept each of the entities together in the the complete loop must be documented to confirm integrity in the form of a Descriptive System Document
For more detailed information please see refer to the specific Intrinsic Safety section.
Notes