Intrinsically Safe vs Non-Incendive: What Is the Difference?

Intrinsically safe equipment limits electrical and thermal energy so it cannot ignite a hazardous atmosphere even when faults occur, which allows use in the most hazardous areas. Non-incendive equipment cannot cause ignition in normal operation, but is not protected against faults, so it is limited to Division 2 or Zone 2 areas.

Both are ways of making electrical equipment safe where flammable gas, vapor or dust may be present. Neither relies on a heavy enclosure to contain an explosion, which is what explosion-proof or flameproof designs do. The difference is how many things are allowed to go wrong: intrinsic safety assumes components can fail, while non-incendive design assumes the equipment is working as intended.

Intrinsic safety works by keeping energy too low to ignite anything, which suits low-power devices such as sensors and handheld radios. A panel PC with a large screen and an Intel Core processor draws too much power for that, so most hazardous area HMIs are non-incendive designs certified for Division 2 or Zone 2.

An intrinsically safe circuit is designed so that the energy available at any point, including in a spark when a wire breaks or shorts, stays below what is needed to ignite the gas. Stored energy in capacitors and inductors is limited too, and surface temperatures are kept below the temperature class.

Where an intrinsically safe field device connects to equipment in the safe area, a zener barrier or galvanic isolator sits between them and caps the voltage and current that can reach the hazardous area. Engineers check each loop with entity parameters: the maximum voltage, current, power, capacitance and inductance the device can accept against what the barrier can deliver. The international standard is IEC 60079-11, and in the US UL 913.

Non-incendive equipment, written nonincendive in US standards, is designed so that nothing in it can produce an igniting spark or hot surface while it is operating normally. Contacts that open and close are sealed or kept at low energy, and surface temperatures are controlled. The US standard is UL 121201, formerly ISA 12.12.01, and the IEC zone system uses comparable concepts such as Ex ec and Ex ic.

Because faults are not covered, non-incendive equipment relies on the area itself being safe most of the time. That is exactly the definition of Division 2 and Zone 2: a flammable atmosphere only appears if something else fails, and the chance of that coinciding with a fault in the equipment is accepted as very low.

A related idea is nonincendive field wiring. Here the equipment in the safe area or the Division 2 area limits the energy on a particular circuit, such as a sensor loop, so that opening, shorting or earthing that wiring in normal operation cannot ignite the atmosphere. That lets the field wiring use ordinary Division 2 methods without barriers, while the rest of the equipment stays non-incendive.

In short, intrinsic safety buys access to the most hazardous areas at the cost of very low power. Non-incendive design keeps normal power but is limited to areas where the hazard is occasional.

The area classification usually makes the decision before the equipment does.

We supply intrinsically safe computers and hazardous area panel PCs for both approaches, and the wastewater HMI case study shows one in use. Each system is integrated and validated as standard within its certified configuration.