Explosive Atmospheres: Intrinsic Safety

Intrinsic Safety (IS) is one of the most widely used types of protection for electrical equipment intended for explosive atmospheres (Ex-equipment). Today, it is practically inconceivable to design a hazardous area without its application. This protection concept is applied to measuring, control, and communication devices in explosive atmospheres and is commonly recognised by its characteristic light blue marking.

While intrinsic safety is only one of several types of protection for electrical Ex-equipment, its versatility has made it one of the most widespread. The principle of intrinsic safety is to prevent ignition of an explosive atmosphere by electrical sparks or hot surfaces. For gases and vapours, typical ignition energies range from 0.01 mJ to 0.3 mJ. Intrinsic safety ensures that by limiting voltage, current, power, inductance, and capacitance, any spark or thermal effect generated within an IS-protected circuit will remain below these ignition thresholds. Thus, an intrinsically safe device is incapable of igniting an explosive atmosphere.

An IS system generally consists of two main parts. The first is the intrinsically safe barrier, usually located in an electrical cabinet outside the hazardous area. Its function is to restrict all electrical parameters of the circuit. This barrier then supplies the second part of the circuit — the intrinsically safe device installed within the hazardous area. Due to the limited available power (typically not exceeding 1 W), intrinsic safety is most often applied to low-power instrumentation and control devices, such as temperature, pressure, position, level, or vibration sensors.

IS devices must comply with the general requirements of IEC 60079-0 and the specific requirements of IEC 60079-11 for intrinsic safety. The protection is marked with the symbol Ex i, which is further subdivided into Ex ia, Ex ib, and Ex ic, denoting different levels of protection. Ex ia provides the highest level of safety and may be used, for example, inside a gasoline tank, while Ex ic represents the lowest level and is suitable only for less demanding applications, such as gas bottle storage facilities.

At SIQ, we test and certify devices with intrinsic safety protection. Certification is carried out in accordance with the 2014/34/EU (ATEX) Directive as well as the international IECEx certification scheme.

More information:
Matej Debenc
E-mail: matej.debenc@siq.si
Tel.: +386 1 4778 227