Hazardous Locations: Know Your Explosion Proof Classifications|
Knowing where hazardous location approved lighting equipment is necessary and determining its proper application can be somewhat daunting to the uninitiated. Hazardous locations are defined by the NEC or “National Electrical Code” as areas "where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitable fibers or flyings." The NEC is a part of the National Fire Protection Association’s publications detailing electrical safety in the industrial and commercial workplace. A portion of the NEC deals specifically with the presence and operation of electrical equipment in hazardous locations precisely because electricity poses a serious potential to cause ignition of the flammable and volatile substances noted above. In an effort to clearly identify and label hazardous locations and the proper procedures for installing and operating electrical equipment within them, the NEC has devoted several chapters and articles in its publication to classification and ratings systems.
The NEC classifies hazardous locations according to three criteria, Type, Condition and Nature. The types of hazardous locations are determined according to the kind of dangerous materials or compounds that are present. An environment where flammable gases or vapors such as petrochemicals or natural gas are present in enough quantities to be potentially flammable or explosive and could be ignited by a spark or heat is considered a Class 1 hazardous location. Thus, chemical processing facilities, utilities and plants handling natural gas and fuels, spray painting booths, aircraft hangars and fueling stations all can be classified as Class 1 hazardous locations and so require electrical equipment used in those areas to be rated Class 1.
A second type of location is one where combustible dusts may be present. Many solid materials that are normally fairly inert can become potentially as flammable and explosive as petrochemicals when ground or pulverized into fine enough particles and suspended in the atmosphere. Locations where dust such as this is present are thus classified as Class 2 locations and so equipment rated Class 2 must be used. Grain silos, flour mills, coal preparation plants, sugar refineries, fireworks factories and plants that machine, manufacture or store aluminum or magnesium metals are all examples of class 2 hazardous locations.
A third type of hazardous location is one where easily ignitable fibers and flyings from machining and working processes are present but not necessarily suspended in the atmosphere. In these locations these materials can accumulate around equipment and machinery where they can then be easily ignited by sparks or heat. In these locations equipment that is classified as Class 3 must be used and include examples areas such as woodworking plants, textile plants, cotton mills, and processing plants.
It should be noted that none of the examples here are comprehensive and only serve to demonstrate the differing hazardous location classifications as they relate to different types of materials.
The second way hazardous areas are rated is according to the conditions of the area. In this case there are only two types of conditions, normal and abnormal. In normal conditions, flammable or explosive materials are present as a regular part of operations and such areas are classified as Division 1. In abnormal conditions, flammable or explosive materials are usually only present in sealed or contained states that do not allow them normal contact with the outside atmosphere. In these cases, the materials become dangerous when leaks, ruptures, breaks or other faulty conditions allow the materials to escape or vent flammable gases or fumes into the surrounding area, thus these are known as abnormal conditions and are classified as Division2. As a result, hazardous areas are usually rated Class 1 Division 1, Class 1 Division 2, Class 2 Division 1 and so on according to their respective types and conditions and thus equipment to be used in such areas must be similarly rated for these areas.
The third criteria for rating and classifying hazardous areas involves the nature of the flammable or explosive materials that are present. In Class 1 locations the natures of materials are grouped through application of the alphabetical designations Groups A, B, C, or D. Each letter represents a different material according to its flammability, volatility, ignition temperature and explosion pressure. Acetylene is the only item listed in Group A and represents an easily ignitable gas with the highest explosive pressures and thus there is little equipment normally available due to the small size of this group. Group B represents another fairly small category and includes hydrogen and other materials with similar traits. Groups C and D make up the largest Class 1 groups and include the bulk of flammable or volatile chemicals, vapors and materials including natural gas, butane and propane. The end result is that a Class 1 area can then be further narrowed according to these other criteria which would then be Class 1, Division 1, groups C and D or Class 1 Division 2 group B for example.
Class 2 dust location Groups include E, F and G where materials are categorized according to ignition temperature and the conductivity of the hazardous materials in question. Conductivity is important because metallic dusts that can conduct electrical current are included. Metallic dusts are contained within Group E. Group F includes materials such as charcoal dust and coal dust. Group G includes grain dusts, flour, starch, pulverized organics and similar materials.
As can now be seen, hazardous locations can be fitted within a specific set of criteria which then makes it possible to correctly select the proper electrical equipment for use within these locations. A paint spray booth for example would have flammable/explosive gases and vapors present as a part of normal operations, making it a Class 1 Division 1 area, while the nature of the materials would fit within Groups C and D. Thus a paint spray booth light rated Class 1 Division 1, Groups C and D would be required. A grain silo where combustible dusts are present during normal operations would be a Class 2 Division 1, Group G area.
The critical aspect to remember here is that each location is different and that just because equipment may be rated explosion proof does not mean it is suitable for any hazardous location. Equipment must be chosen according to the specific type, nature and conditions that are present and be appropriately labeled and approved for these areas in order to conform to federal and local regulatory guidelines.