Explosion Proof Lighting is a light fixture that has the unique ability, in case of an internal explosion, to contain this event inside the fixture. If a spark creates an explosion inside an explosion proof fixture, the fixture is designed not to transfer this explosion to its external environment. Explosion proof lighting is all about containment. That is why they are extremely robust fixtures with thick metal walls and glass.

Lights that are Explosion Proof rated are certified and tested and must pass a specific standards to ensure they are safe. The most common classes are Class 1 Division 1 and Class 1 Division 2.

The major difference between these two classes is the existence of combustible materials in the surrounding environment. In Class 1 Division 1 environments, these gases, vapors or materials are commonly present. In Class 1 Division 2 environments, these same explosive materials, gases or vapors are present at times but not all the time.

Explosion proof lighting is a special type of product designed to withstand the toughest environments, specifically hazardous locations.

Per Article 500 of the National Electrical Code (NEC), an area is considered a hazardous location when there are (or may be) ignitable concentrations of combustible substances in the air. These substances include vapors, dust, certain fibers, and flammable gasses. To be considered explosion proof, a lighting fixture must be able to contain an internal combustion by preventing it from propagating outside the unit.

Many people assume that these fixtures work via a seal around the bulb (and its other components), which prevents flammable compounds from entering the device. However, that's only half the story. Explosion proof lighting contains a unique feature called a flame path, which is a special type of joint between different parts of the enclosure. This flame path is essentially a controlled leak that allows expanding gasses from an internal explosion to cool and safely vent to the outside, without igniting any explosive atmosphere that may be outside the lamp. The class, division and group that the enclosure is rated for determines the allowable leak rate (flame path gap and length) to prevent external ignition.

It is worth noting that products that are appropriate in hazardous areas are not always explosion proof. There are many other methods to mitigate explosion risk. Other techniques include intrinsic safety, encapsulation, oil immersion, pressurization, and so on, depending on each application’s specific needs. Project managers should review a product's certifications prior to bringing it to the job site to ensure the equipment is appropriate for their specific application.