Intrinsically safe describes electrical equipment and circuits designed to limit electrical and thermal energy so they cannot ignite flammable gases, vapors or dusts, even when a fault occurs in a hazardous location.
Intrinsically safe (IS) describes electrical equipment and wiring designed so that, under normal operation and specified fault conditions, it cannot release enough electrical or thermal energy to ignite a flammable atmosphere. Rather than containing an explosion or keeping flammable gas away from sparks, intrinsic safety works by keeping the energy in the circuit so low that a spark or hot surface simply is not strong enough to cause ignition.
Intrinsic safety is one of several protection methods for electrical equipment used in hazardous (classified) locations, where flammable gases, vapors, combustible dusts or ignitable fibers may be present. It is especially common for low-power devices such as gas detectors, sensors, transmitters, radios, flashlights, handheld meters and tablets used in refineries, chemical plants, mines, grain elevators, pharmaceutical facilities and fuel terminals.
Because intrinsically safe equipment removes the ignition source at the design level, it allows work and live maintenance to take place in areas where ordinary electronics would be a serious explosion hazard. The protection only holds, however, when the whole system, including barriers, cables and connected devices, is designed, installed and maintained according to its certification.
Every flammable gas, vapor or dust has a minimum ignition energy, the smallest amount of energy that can set it off. Intrinsically safe circuits are designed to stay well below that energy, even if components fail, wires short together or connections break. Designers limit voltage, current and stored energy in capacitors and inductors so that any spark that could occur is too weak to ignite the surrounding atmosphere.
Hot surfaces can also cause ignition. Intrinsically safe equipment is assigned a temperature class, or T-code, that shows its maximum surface temperature. The T-code must be lower than the autoignition temperature of the gases or dusts that may be present.
Field devices in the hazardous area are usually connected to control systems in a safe area through associated apparatus, such as zener barriers or galvanic isolators. These devices limit the energy that can pass into the hazardous area, even if a fault occurs on the safe side, such as mains voltage being applied by mistake.
To ensure an IS system stays safe, the electrical characteristics of the field device, the barrier and the cable must be compatible. Certified equipment lists entity parameters, such as maximum voltage, current, capacitance and inductance, and system designers check that the combination stays within those limits.
Whether intrinsically safe equipment is needed depends on how an area is classified under the National Electrical Code (NFPA 70) or international standards.
Classes are further divided into groups based on the specific material, such as hydrogen or propane, because different materials ignite at different energies.
The zone system, used internationally and also recognized in the NEC, divides gas atmospheres into Zones 0, 1 and 2, and dust atmospheres into Zones 20, 21 and 22, based on how often and how long the hazard is present. Intrinsic safety is one of the few protection methods suitable for Zone 0, where a flammable atmosphere is present continuously or for long periods.
Intrinsically safe equipment must be tested and certified by a recognized testing laboratory. In the United States, UL 913 is a key standard. Internationally, IEC 60079-11 applies, and certification schemes such as IECEx and the European ATEX directive are widely used. Markings on the device show where it may be used, for example Class I, Division 1, Groups C and D, or an Ex ia marking, which indicates the highest level of intrinsic safety protection.
A fuel distribution terminal wanted to give operators tablets for digital inspection checklists and work permits. A supervisor bought consumer tablets in rugged cases, and operators began carrying them into the loading rack area, which was classified as Class I, Division 1 because gasoline vapors are present during normal loading. During an internal audit, the safety coordinator flagged the tablets as uncontrolled ignition sources in a classified area.
The terminal pulled the consumer tablets from the loading rack and replaced them with tablets certified as intrinsically safe for Class I, Division 1, Group D, with matching certified chargers kept in the control room. It also posted signs at the boundary of the classified area restricting personal electronics, added hazardous location ratings to its purchasing approval process for any electrical equipment, and updated its hot work and permit procedures to include a check of all electronics brought into the area.
Explosion-proof equipment is built with a heavy enclosure strong enough to contain an internal explosion and prevent flames from escaping. Intrinsically safe equipment prevents ignition in the first place by limiting energy. IS equipment is usually lighter, smaller and safer to maintain while live, but it is limited to low-power devices.
No, not unless it is a specially certified model with markings showing its hazardous location rating. Standard smartphones and tablets can produce sparks or heat if damaged or faulty and should not be used in classified areas.
Generally no. Repairs or modifications can change the energy limits that the certification depends on. Follow the manufacturer's instructions and use authorized repair facilities.
No. Each device is certified for specific classes, divisions or zones, gas or dust groups and temperature classes. It must match the classification of the area where it will be used.
Part of SafetyIQ's EHS glossary: plain-English definitions of workplace health and safety terms.
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