Explosion Proof and Intrinsically Safe Fundamentals|
Hazardous locations represent some of the most demanding and dangerous work environments in the world today. These work areas are designated as hazardous by regulating bodies such as OSHA due to several characteristics typical of such locations. These characteristics can be the enclosed nature of the workspace which allows volatile gases or vapors to become concentrated, the presence of flammable or volatile petrochemicals, or the presence of volatile fine particulates just to name a few, each of which can create an explosion or fire hazard.
Prevention is the most important aspect of controlling the risk of fire or explosion in hazardous locations. Many of the instances where explosions or fire have occurred in the industrial or commercial workplace are the result of what is known as inadvertent ignition. Inadvertent ignition occurs when something as simple as the spark from a light switch or the heat from a lamp ignites volatile compounds or materials, resulting in fire or explosion. All electrical devices regardless of their type produce some potential for spark or heat. As most hazardous work areas necessitate the use of electrical equipment in their operations, controlling the possibility of inadvertent ignition these electrical devices present is critical to the safety of the workplace.
In regards to illuminating hazardous locations, control and prevention is practiced through the use of what is termed explosion proof or intrinsically safe lighting. These types of luminaries are designed to prevent inadvertent ignition caused by the sparks or heat that could possibly be produced by this equipment. This is achieved through special designs, voltage limitations and heat controls that reduce or remove the possibility of sparks, heat or flame created by these lamps.
Intrinsically safe and explosion proof lighting equipment are not the same and each fulfills a different role according to its ratings. Ratings determine the suitability of electrical devices for use in hazardous locations according to type of environment each hazardous location represents. Ratings are represented by Classes, Divisions, Groups, and or Zones, and each carry within them differing levels represented by a numbering system. Thus, explosion proof lighting equipment will be rated for use in Class-1 Division-1 or Class-1 Division-2 environments for example. Each rating level represents a different type of environment according to the types of hazardous materials and conditions that may be encountered. Therefore, if an area is designated a Class-1 Division-2 work area, then only equipment rated as Class-1 Division-2 may be used within it. This means that not only must explosion proof luminaries be rated as explosion proof, but they must also carry the proper ratings according to the environment they will be used in. As a result, just because a lamp is rated as explosion proof, does not mean it is suitable for use in all hazardous locations.
Intrinsically safe luminaries are of a different order than explosion proof luminaries. Explosion proof luminaries are typically higher powered and are generally designed to contain ignitions or explosions within their housings long enough to allow any heated escaping gases to cool below ignition temperatures before they can exit the lamp. Intrinsically safe luminaries on the other hand are typically low powered and incapable or producing enough heat or sparks to produce any ignition at all.
Explosion proof and intrinsically safe lighting equipment is rated and approved by accredited bodies such as Underwriters Laboratories. Once equipment is approved, it must carry somewhere on its housing labeling which certifies this approval. Any equipment sold, marketed or represented as suitable for hazardous locations, regardless of the manufacturers claims, must carry this approval or it is not in conformance with regulatory laws and guidelines and thus not safe for use in hazardous locations.
This is little more than a primer covering the very basics of explosion proof lighting. Anyone interested in learning more should consult with OSHA or the National Electrical Codes which are published with the National Fire Codes series produced by the National Fire Protection Association.