The Simple Basics of Hazardous Location Lighting Ratings|
Article- May 2013 By Larson Electronics.com
Larson Electronics Class I, Div. I & II Emergency Lighting System
Some of the most commonly misunderstood terms in industrial lighting involve equipment designed for use in specific locations where various hazardous and non hazardous materials might be present. Industrial and oftentimes commercial operations involve a variety of substances that depending on their nature or characteristics can pose potential problems when they are in close proximity to electrically powered devices. The type of hazard and its severity depends greatly on the material in question and can range from a potential for damage and eventual failure of the equipment being used, to a risk of fires or explosions that can result in serious injuries or even death. The problem arises from the fact that the terms used to describe equipment designed for use in proximity to these hazardous materials can be easily misunderstood, resulting in equipment that is improperly rated being used in a potentially dangerous location.
Some of the most common terms encountered with industrial lighting designed for use in hazardous locations include, Explosion Proof, Intrinsically Safe, and Vapor Proof. As you can imagine, the first impression a layman gains just from an initial observation of the terms may be entirely different than what the term actually means. For instance, one of the most common misperceptions among those unfamiliar with industrial lighting is that lighting labeled as “Explosion Proof” is able to withstand exposure to an explosion and continue operating. While a second consideration would probably invoke our common sense (what good would a light surviving an explosion be if the person using the light were exposed to the explosion as well?), this misconception remains one of the most commonly encountered. Some other misconceptions are more nuanced and involve incorrect assumptions, for instance, that vapor proof lighting is safe to use in a flammable atmosphere since vapors cannot enter the housing. This of course is false, but underscores how easy it is to make an erroneous assessment of electrical equipment based solely on its general description.
Electrical equipment and lighting in particular intended for use in specialized applications due to concerns with potentially hazardous materials being present in a given location must be properly rated and approved for those locations according to the nature of the hazards. As it pertains to electrical equipment, a hazardous location is an area where the presence of flammable or explosive vapors, gases, flammable liquids, combustible dusts, or ignitable fibers or flyings poses a potential fire or explosion risk. For an example, the area in and around an automotive paint spray booth represents a hazardous location because of the flammable gases and vapors given off by the various paints and solvents used during operations. In such locations as these, two types of fixtures which include Explosion Proof and Intrinsically Safe will be required.
Explosion proof light fixtures and electrical devices in general, are designed not to withstand an explosion, but to prevent the device from causing the ignition of flammable atmospheres and materials outside the fixture. There are variations on the methods used to accomplish this, but the most common involves a sealed housing that is designed to contain any ignition of gases or vapors WITHIN the housing long enough so that when they finally do exit, they have cooled enough to be unable to ignite those same vapors or gases outside the housing. Usually this is accomplished through a series of threads or channels joining the various parts of the housing together. When an ignition takes place within the housing, the hot gases must follow these series of channels or threads before they can exit, this in turn slows them down enough to allow sufficient cooling to take place before exit.
Intrinsically safe fixtures rely on a design that renders them essentially incapable of causing an ignition at all. With these forms of lighting, the design is such that there is little heat produced, and the currents utilized are too weak to cause an ignition source, even in the case of internal failures or shorts. These devices are also typically fully sealed and may incorporate internal circuits, sensors and relays which can limit or end current supply in the event of a device failure. Intrinsically safe light fixtures are less common than explosion proof rated fixtures, in large part because they are typically low powered and thus limited in their ability to produce enough luminosity for large scale lighting applications. You’ll typically find devices such as portable flashlights and lanterns, indicator lights, and small LED fixtures to make up the majority of intrinsically safe rated lighting devices.
The main point to understand with both intrinsically safe and explosion proof rated fixtures is that they are not a one size fits all lighting solution. Explosion proof lighting is rated and certified according to a classification system that takes into account the basic nature of the hazardous environment according to the type of materials that are present, the specific type of flammable or explosive materials present, and the likelihood of their presence. This classification is denoted as Class, Division, and Groups, and in order for a light to be suitable for a specific type of environment it must carry a matching or higher rated classification rating for the classification of the area it is to be used within.
Vapor proof fixtures are perhaps responsible for some of the most common misunderstandings in industrial lighting safety. As we noted earlier, the term “Vapor Proof” can be misleading because upon first glance it would seem obvious that a fixture impervious to the intrusion of vapors within its housing should be safe in a hazardous environment.
This is not the case however, and regardless of a fixtures’ vapor proof rating, unless it carries explosion proof or intrinsically safe certification it is not safe for use in hazardous locations. Vapor proof lighting does offer some protection from effects such as corrosion and humidity in locations where these conditions can be a problem, providing a lighting solution that can withstand these conditions while maintaining a high degree of reliability.