Despite its critical nature, explosion proof lighting is quite often wholly misunderstood both in its basic nature and varying types. Tell someone their location requires an explosion proof light fixture and the first thing they’ll likely assume is you mean a light that cannot explode. There is even more often a misunderstanding regarding the various types of safety lighting available and a lot of mistaken assumption that one type is interchangeable with another. For instance, some may assume that because a fixture is vapor proof it is safe to use in areas where flammable or explosive vapors are present, and thus is comparable to an explosion proof fixture. Nothing could be further from the truth, and such misunderstandings can lead to serious injury or even death.

Explosion proof lights are lamps and fixtures that have been designed specifically for use in areas where dangerous flammable, explosive or otherwise volatile gases, vapor, liquids and materials are or may be present. Locations such as these are considered “Hazardous Locations” and are defined by different codes and directives such as the NEC (National Electrical Code-USA), ATEX (European Union), CEC (Canadian Electrical Code) and similar codes and regulations. Such locations can have materials such as petrochemicals, explosive dusts, solvents and fibers which are present as a part of everyday operations or could be present under unusual conditions such as a container or pipeline leak. Regardless of when these locations have flammable or explosive materials present however, the electrical equipment used in locations classified as hazardous must comply with regulations and laws based on electrical codes regarding hazardous locations.

At the basic level, explosion proof lighting is equipment designed to prevent the ignition of flammable or explosive materials, gases, or vapors. Lighting is one of the most commonly encountered electrical devices in any type of workplace and the types of lighting used can range from high power permanent fixtures to a common flashlight used for portable illumination. Every type of light used in a hazardous location must be explosion proof certified regardless of its size or type. Since lighting equipment operates on electrical current, and electrical current can create heat or sparks, it must be properly designed specifically for use in hazardous locations if flammable or explosive materials may be present. Lighting can present an ignition danger in several ways, including but not limited to; the operating heat of the lamp, the minute sparks created by on/off switches, defective wiring or internal components which can lead to short circuiting, or heat buildup from the accumulation of dusts or fibers on the fixture. As a result, the manner in which lighting equipment meets regulatory compliance for hazardous locations can vary and is usually reflected by its design and the type of approvals it carries.
 

Lighting for hazardous locations must be certified explosion proof or intrinsically safe by an authorized third party testing organization such as Underwriters Laboratories which tests and certifies equipment according to the relevant electrical codes set out by the NEC, ATEX etc. Intrinsically safe and explosion proof certification is similar, however the two terms denote different levels of design which reflect how they protect against ignition. Explosion proof equipment is designed to withstand and contain the ignition of flammable materials within the fixture itself, whereas intrinsically safe equipment does not produce or carry enough electrical current to cause ignition. For all intents and purposes, intrinsically safe lighting represents the highest level of safety, while explosion proof lighting meets minimum requirements for a much wider variety of environments. Intrinsically safe lighting tends to be small, low powered, and impractical for general lighting applications, and so is much less common than explosion proof lighting which generally encompasses more powerful fixtures.

Explosion proof lights do not prevent ignition completely, but rather control it and prevent the atmosphere outside of the light fixture from igniting. This is accomplished in a few different ways, but the general premise is to contain an ignition within the lamp housing long enough for the ignited gases to cool before escaping from the fixture. Explosion proof lights are generally constructed of heavy gauge, thick walled metals such as aluminum for rigidity and strength. The joints are typically fitted together with fine threads which serve a dual purpose; they provide a strong joint that can withstand an internal explosion, and they actually allow the pressures created by an internal explosion to escape. They do this safely by forcing the escaping heated gases to slow down to the point that by the time they exit the fixture, they have cooled enough to be unable to ignite the atmosphere outside the light fixture.

So as can be seen, it is not that explosion proof lights cannot explode, but rather they can withstand and contain an explosion or ignition within themselves. In addition to being certified explosion proof, lighting for hazardous locations must also be approved for use around the different types of conditions and materials they might come into contact with. Hazardous locations are rated according to the likelihood of the hazardous condition, and the types of materials which make the area dangerous. Thus, locations are defined as Class 1 which refers to Gases or Vapors, or Class 2 which denotes combustible or electrically conductive dusts. Additionally, locations are further sub categorized according to the likelihood of the hazardous condition existing, with Division 1 denoting the presence of hazardous materials under normal conditions, and Division 2 denoting their presence under abnormal conditions such as a container leak. Locations are also broken down according to the types of materials and classified as Groups A through G. For a detailed description of hazardous location classification refer to our article "IECex/ATEX and North American NEC HAZLOC Equipment Classification".

To be suitable for a given hazardous location, a fixture must be certified according to Class, Divison, and Group. Thus, a Class 1 Division 1 Group C locations requires equipment carrying Class 1 Division 1 Group C certification. If the fixture does not carry this certification, it is not suitable for use in hazardous locations regardless of any manufacturer claims as to it being explosion proof.