What is “Explosion Proof”?

First, ‘explosion proof’ does not mean that the object, say an enclosed engine, will be unscathed in an explosion caused by an outside source. What is does mean, is that the enclosure surrounding the object itself will prevent and contain any internal ignition from creating a blast outside of the object’s enclosure. The highest temperature created by the object and its enclosure must not exceed the explosive/combustive limit of the gases, dusts, and other ignitable elements in the area surrounding the object.

On a very basic level, explosion proof insulations and enclosures prevent the conditions necessary to create an explosion in the environment in which they are used.


What can go wrong if components, engines, and machinery aren't explosion proof?

As an example, think of the internal combustion engine. Because internal combustion engines bring in air from the outside to create the fuel to air ratio that powers them, this delicate balance can be upset if that outside air contains flammable agents. For instance, additional gases brought into an internal combustion engine increase the fuel to air ratio resulting in pre-ignition conditions. If the temperature of the operating motor reaches the auto-ignition temperature of the mixture of the inherent and new fuel sources, an explosion occurs.

Persons working on a daily basis with flammable and explosive materials know that there are not always observable indicators of an atmosphere that could ignite. Many gases have no scent and are not visible, and unless you know what you’re looking at, dust doesn’t always look as dangerous as it can be. A novice in a shop might not be aware of, or know what hazards to look for before turning on an unprotected motor. Should gases and dust ignite, an explosion could occur with additional hazards such as flashback and could cause loss of property, lost work, and even death.

It doesn’t have to be a spark that causes an explosion. Temperature alone can set the stage for ignition. A hot exhaust pipe that is above the explosive limit of the gases or dust particles that were brought into the engine and are now on their way out can ignite and cause flashback throughout the entire machine.

Common Methods for Containing and Controlling Explosions

It is important to know that sparks are not the only cause of ignition – that high temperatures can be an ignition source.

In addition to explosion proof enclosures, explosion proof insulation and high temperature insulation of machine components such as exhausts, manifolds, and turbo chargers brings potentially high temperatures down to a level tolerated by area gases and dusts. While this may seem overly simple, it is possible to reduce temperatures by more than 440% with proper insulation.

The method used to explosion proof or dust ignition proof your equipment depends on what hazardous materials classifications, divisions, and standards it falls under.

Common Explosion Proof Terminology

Explosion proof – Apparatus is enclosed in a case that is capable of withstanding an explosion of a specified gas or vapor that may occur within it and of preventing the ignition of a specified gas or vapor surrounding the enclosure by sparks, flashes, or explosion of the gas or vapor within, and which operates at such an external temperature that a surrounding flammable atmosphere will not be ignited thereby.

Dust Ignition proof – protection that excludes ignitable amounts of dust or amounts that might affect performance or rating and that, when installed and protected in accordance with the original design intent, will not allow arcs, sparks or heat otherwise generated or liberated inside the enclosure to cause ignition of exterior accumulations or atmospheric suspensions of a specified dust.

Intrinsically safe – A type of protection in which the electrical equipment under normal or abnormal conditions is incapable of releasing sufficient electrical or thermal energy to cause ignition of a specific hazardous atmospheric mixture in its most easily ignitable concentrations. This type of protection is referred to as “Ex i”.
Explosion containment: The only method that allows the explosion to occur but confines it to a well-defined area, thus avoiding the propagation to the surrounding atmosphere. Explosion-proof enclosures are based on this method.

Segregation  A method that attempts to physically separate or isolate the electrical parts or hot surfaces from the explosive mixture. This method includes various techniques, such as pressurization, encapsulation, etc.
Prevention: A method that limits the energy, both electrical and thermal, to safe levels under both normal operation and fault conditions. Intrinsic safety is the most representative technique of this method.