Explosion Proof and Intrinsically Safe: There is a Difference|
When it comes to explosion proof lighting many people have trouble understanding exactly what the term means. Factor in that there is also the term “intrinsically safe light” which is related to explosion proof lighting, and the fact that few people have had the benefit of a good layman explanation of the terms, and it becomes clear that there is plenty of room for confusion. A clear explanation of the terms is important to understanding what these terms mean and here we will try to provide that explanation in order to clear up some of the confusion.
To begin with we need to talk in generalities and give a brief description of what explosion proof lights are used for. Explosion proof lights are special lamps constructed specifically for use in volatile environments, or more accurately termed “Hazardous Locations”. The definition of a hazardous location is determined by regulating bodies for a given region such as the National Electrical Code as carried by OSHA in the United States. Hazardous location refers to areas where there is a high enough concentration of volatile or combustible substances in the air to present a high danger of fires or explosions. These substances need not be only vapors or fumes from volatile fuels or solvents like gasoline or paint thinner, they can also be fine particles such as dusts like flour or sawdust. The high danger of fires and explosions that these substances present has resulted in laws that require workers to use equipment specially designed to reduce and prevent the chances of igniting these materials which could cause catastrophic combustion.
Any electrical equipment that is going to be operated in a hazardous location presents a possible ignition source. Everything from switches to electric motors are capable of producing sparks or electrical arcing that can ignite flammable substances if they come into contact with them. The most commonly present electrical equipment in hazardous locations is lighting and any lighting to be used in these locations must be designed to prevent the chances of inadvertent ignition. For use in hazardous locations there are two basic choices for electrical illumination, the intrinsically safe light, or the explosion proof light. Although both can be used in hazardous locations, the design behind these lights is based on different principals with explosion proof lights being designed to contain an ignition within the light itself, while intrinsically safe lights care incapable of providing enough electrical energy to create a spark or heat that could act as an ignition source.
Explosion proof lights are designed to be extremely durable. Lights like the Larson Electronics EPL-PM-1X300-100 are designed to actually contain an explosion within their housings which as you can imagine is no minor feat. The body is made out of heavy cast aluminum alloy that contains no copper to prevent sparks from impacts, with oil and abrasion resistant electrical cord that has an explosion proof connector at its end. It’s water resistant and can be used in wet conditions and is suitable for use in marine environments and the lamp is a 300 watt halogen to provide bright illumination while keeping heat to acceptable levels. This is important as halogen lamps over 400 watts produce a great deal of heat and any explosion proof rated halogen lamp that operates over 400 watts must be designed with further considerations for managing this heat.
Just because a lamp is explosion proof certified however does not mean it is acceptable for use in all hazardous locations. Explosion proof lamps have to be certified explosion proof by a sanctioning body like Underwiters Laboratories and are rated according to the type of hazardous location they will be operated in. These classifications consist of a Class, Division, Groups and Zones and each is based on a specific set of criteria determined by the types of hazardous materials and conditions that may be present. This means that a light must approved according to these classifications and a light used outside of its classification will not adhere to the proper regulations even if it is rated explosion proof. For example the Larson Electronics EPL-PM-1X300-100 mentioned above is rated Class-1, Division-1, Group-D. This means that this light is suitable for all classes and divisions lower than 1 but not groups higher than D.
The confusion between explosion proof lights and intrinsically safe lights arises mainly from the assumptions as to what these lights are intended to do. Since the light is called “explosion proof”, the first assumption is that the lamp is incapable of causing an explosion. This is an erroneous assumption as the light is indeed capable of causing an explosion. It earns an explosion proof rating because it is capable of containing an explosion within itself, preventing that explosion from escaping at temperature levels that could ignite substances present in the atmosphere outside of the lights housing. So while an explosion proof light may not be airtight and perfectly sealed, it is designed to contain an explosion long enough to allow the escaping heated gases and material from that explosion to cool below temperatures capable of causing ignition. Many explosion proof lights accomplish this through the use of fine threads when joining the parts of the lamps assembly together. These threads create a long channel that escaping gases must travel along before they can exit the lamps housing. By the time they finish traveling along these channels and escape from the units housing, these gases have cooled to a temperature that is well below that required to ignite flammable materials.
Intrinsically safe lights are different, in that as well as being constructed of materials that are incapable of or resist creating sparks, they are also sealed and do not operate on enough current to produce sources of ignition. A good example would be an intrinsically safe LED flashlight. A flashlight like this operates on low amperage batteries and the LED lamp uses very little electrical current to produce light, resulting in very little heat and too little energy to create ignition should it be exposed to a volatile atmosphere.
These are just the basics of explosion proof and intrinsically safe lighting. There is a great deal more involved and choosing the right lamps for your application will require a more in-depth understanding of all the ratings and classifications that are related. Larson Electronics provides additional information about these ratings on its website and you are encouraged to read it through in order to fully understand how these classifications work and how they apply to electrical equipment.