The concept of explosion proof light ratings can be confusing to understand. Hazardous workplace conditions can vary greatly and that means that a comprehensive rating system becomes necessary in order to ensure a safe work environment. There are a wide variety of explosion proof equipment including explosion proof light towers, explosion proof string lights, explosion proof exit signs, and various other versions of hazardous area lighting. Understanding the way these lights are classified is important in order to make an informed decision on which type of light is right for a specific workplace.
Definition and Construction of Explosion Proof Lighting
Let’s clear up the very first misconception that is present when talking about explosion proof lighitng, and that is the very term explosion proof. A light fixture that is rated to be explosion proof does not mean that light is built to survive an explosion. Instead, it simply means that it is designed to prevent the device from being the cause of an external explosion.
For example, a Class I Division 1 fixture is designed to contain an explosion within the fixture should the internal components start one. External heat from the environment or location where the light is located will not cause an explosion nor will the light’s housing allow a spark or arc to start an ignition. As one gets further into the classification system, differences in the explosion proof qualities of various explosion proof equipment will begin to become clear.
A Class I Division 2 light are not held to as high of a standard as Division 1 products. To meet the requirements for Division 2, a light does not have to be able to contain an explosion. Instead, they must be found to be unable to cause an explosion in environments for which they are approved to be used. The approved environments are designated through a selection of different groups that contain various hazardous work locations. An intrinsically safe light is a light that will not cause any explosion whatsoever.
This can be accomplished in several different ways depending on the design of the light, but the most common way is for the fixture to contain any ignited flammable vapors or gases within the light itself for a duration of time that renders them cool enough to prevent further ignition of vapors in the work place atmosphere once they finally exit the light. These methods of ensuring only cool enough gases are released from any explosion proof equipment can vary depending on the design and classification of each item.
Once the definition of explosion proof is understood, it becomes clear that explosion proof lighting is not a one size fits all solution to any hazardous work area or location. In fact, an explosion proof light that is safe for one work location may be a real danger in another. That is why it is important to become educated on the classification system and the type of work environments it encompasses.
Understanding Class and Division
There are three classes of explosion proof lights known as Class I, Class II, and Class III. These are the broadest sense in which explosion proof lights are distinguished from each other. The classes are each broken down further into two separate divisions.
Here are the three classes and their corresponding divisions:
Class I, Division 1 – Where ignitable concentrations of flammable gases, vapors or liquids are present continuously or frequently within the atmosphere under normal operation conditions.
Class I, Division 2 – Where ignitable concentrations of flammable gases, vapors, or liquids are present within the atmosphere under abnormal operating conditions.
Class II, Division 1 – Where ignitable concentrations of combustible dusts are present within the atmosphere under normal operation conditions.
Class II, Division 2 – Where ignitable concentrations of combustible dust are present within the atmosphere under abnormal operating conditions.
Class III, Division 1 – Where easily ignitable fibers or materials producing combustible flyings are present within the atmosphere under normal operation conditions.
Class III, Division 2 – Where easily ignitable fibers or materials producing combustible flyings are present within the atmosphere under abnormal operating conditions.
Locations that are classified in Class III are as follows: Rayon, cotton and textile mills, cotton gins, cotton-seed mills, flax-processing plants, clothing manufacturing plants, woodworking plants, and other manufacturing and processing plants in which combustible fibers and flyings are used in the manufacturing process.
Materials present in a Class III environment are as follows: rayon, cotton (including cotton linters and cotton waste), sisal or henequen, istle, jute, hemp, Spanish moss, excelsior, tow, cocoa fiber, oakum, and baled waste kapok.
Note: These classifications only apply to the United States and were developed by the National Fire Protection Association in their National Electric Code. There is some cross compatibility with Canada in this regard.
Breaking Down The Groups
Although the classes and divisions system makes a strong push towards ensuring all work environments have safe lighting installed, further detailing of each hazardous working environment is necessary due to the wide range of flammable materials that could be present in different industries.
The classification system solves this problem through the use of groups. The different groups, and the classes they are associated with, are listed below:
Class I Groups
Group A: Acetylene
Group B: Hydrogen
Group B Exceptions: Exception 1) Group D equipment can be used in Group B atmospheres containing butadiene as long as all conduit runs into explosion-proof equipment have explosion-proof seals installed within 18 inches of the enclosure. Exception 2) Group C equipment can be used in Group B atmospheres containing allyl glycidyl ether, n-butyl glycidyl ether, ethylene oxide, propylene oxide, and acrolein as long as the same requirements in Exception 1 are met.
Group C: Propane and Ethylene
Group D:
Benzene, Butane, Methane & Propane
Group D Note: Ammonia atmospheres have a different classification of areas and do not fall completely within Group D or any other of the groups mentioned in this article. For more information on this, read ANSI/ASHRAE 15-1994, Safety Code for Mechanical Information and ANSI/CGA G2.1-1989, Safety Requirements for the Storage and Handling of Anhydrous Ammonia.
Class I Group Exception: Carbon disulfide is a chemical that requires safeguards beyond what is required for most other Class I groups due to its low autoignition temperature and the smaller joint clearance permitted to arrest the resulting flame.
Class II Groups
Group E: Metal Dust- This includes aluminum, magnesium, and their commercial alloys and other combustible dusts that present similar hazards in the presence of electrical tools and equipment.
Group E Note: Not all metal dusts fall into this classification. Zirconium, thorium, and uranium dusts have much lower ignition temperatures and minimum ignition energies lower than any material that falls within Class I or Class II. These dusts require further safeguards.
Group F: Carbon and Charcoal- Examples include coal, carbon black, charcoal, and coke dusts.
Group G: Combustible dusts not included in Group E or Group F. These include flour, grain, wood, plastic and chemical dusts. Certain dusts may require additional precautions.
Class III Groups
Class III contains no groups and is broken down only into Division 1 and Division 2 for fibers and flyings.
Larson Electronics manufacturers a wide variety of explosion proof lighting equipment, including the following explosion proof lights:
At Larson Electronics, we do more than meet your lighting needs. We also provide replacement, retrofit, and upgrade parts as well as industrial grade power accessories. Our craftsmen can custom build any lighting system and/or accessories to fit the unique demands of your operation. A commitment tohonesty, quality, and dependability has made Larson Electronics a leader in the lighting and electronics business since 1973. Contact us today at 800-369-6671 or message sales@www.larson-electronics.com for more information about our custom options tailored to meet your specific industry needs.
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