In Part 1 of our guide to selecting the proper enclosures for industrial power systems, we explored the enclosures rated for non-hazardous locations (1-6 & 12-13). Before choosing the right enclosures for your industrial power systems, it’s important to understand what specific closures are rated for and where they will likely be found.
The other group, 7-10, covers hazardous conditions, as classified by NFPA 70. This includes explosion protection from chemicals or combustion and indoor industrial applications where airborne particulate solids, corrosive chemicals, solvents, lubricants, and coolant chemicals may be present. Where such hazardous conditions may exist in outdoor locations, a multi-enclosure fitout may be more appropriate.
In this blog, we’ll look at those enclosures rated for hazardous locations (7-10), how those classifications are determined, and what each rating means.
NFPA 70 Hazardous Locations Classification
The NFPA 70 classification for hazardous locations is rated for the dangerous materials that may be present in the environment and are broken down as follows:
Class 1
Denotes that flammable gasses, vapors, or liquids may be present.
Division 1 or 2
Denotes how often these materials are expected to be present, roughly:
Division 1- They would be expected under normal operating conditions and during maintenance or repair operations, leakage, or equipment breakdown.
Division 2- They would only appear under abnormal circumstances (when buildups of gasses or vapors can occur accidentally) or are adjacent to a Class 1 Division 1 location. The location will have positive mechanical ventilation, and any hazardous materials will be confined within closed containers when handled or used.
Groups
The hazardous materials are further divided into groups, i.e.:
A: AcetyleneB: Hydrogen, Butadiene, Ethylene oxide, Propylene oxideC: Diethyl Ether, Acetaldehyde, Cyclopropane, Dimethyl HydrazineD: Hydrocarbons, fuels, solvents (Gasoline, Butane, Benzene, Acetone, Ammonia, Methane, Propane, Alcohols etc.)
Class 2
This refers to combustible dust. Finely pulverized materials, later suspended and accumulating in the atmosphere, can cause powerful explosions when ignited.
Division 1 or 2
Division 1 means that ignitable quantities of dust are normally present or suspended in the environment. It may also mean that conductive dust may be present.
Division 2 means suspended dust is not normally in an ignitable concentration, though it may accidentally exist. Hazardous buildups of dust layers are also present.
Groups
E: Metal dust, both conductive and explosive (aluminum, magnesium, and their commercial alloys)F: Carbonaceous dust, highly combustible and also possibly conductive (carbon black, charcoal, coal, and coke)G: Other combustible dust (Flour, starch, wood, grain, combustible plastic or chemical dust)
Class 3
This refers to ignitable fibers and flyings—scraps, threads, and other materials that may catch fire when concentrated.
Division 1 or 2
Division 1 means the materials are commonly present, used, or handled in production.
Division 2 means they occur outside the manufacturing process, i.e., handled in storage.
Group
The dust in Class 3 includes those occurring from manufacturing, such as textiles, woodworking, etc. These are hazardous as they are easily ignitable; however, they are not likely to be explosive.
NEMA Enclosure Ratings for Hazardous Locations (7-10)
NEMA 7
Details: This enclosure is designed to protect against gasses and vapors and is rated for use in indoor locations classified in NFPA 70 as hazardous, namely Class 1, Division 1, Groups A, B, C, or D. As with all enclosures for hazardous locations the letter designating the vapor or gas it’s rated against should appear on the enclosure. The enclosure is designed to prevent internal explosions from causing an external hazard to surrounding personnel or igniting further explosions.
Uses: Type 7 enclosures are designed for use where combustible gasses, vapor, or liquids are commonly present. This includes premises such as waste disposal areas, utility gas plants, spray finishing plants, and gasoline storage and dispensing areas.
NEMA 8
Details: These enclosures are also rated for use with Class 1, Division 1 environments with the presence of Groups A, B, C, and D. However, the enclosures are rated for both indoor and outdoor use and are built in accordance with UL698. They are designed to prevent combustion by using oil-immersed equipment.
Uses: These enclosures can be deployed outdoors at petrochemical processing plants, fertilizer plants, and petroleum refineries.
NEMA 9
Details: Type 9 enclosures are designed for indoor use in locations classified as Class 2, Division 1, Groups E, F, or G. That is, they are designed to protect against the ignition of combustible dust. The enclosure should have a letter after ‘NEMA 9’ to show which type of dust it is rated against. The enclosures are designed to prevent the ingress of explosive amounts of hazardous dust, and any gaskets used must be mechanically attached and made of a noncombustible, non-deteriorating, vermin-proof material.
Uses: These are rated for indoor use and can be found in grain elevators, flour and feed mills and certain production plants where combustible dust is created, including plastics, starch, and medicines producers.
NEMA 10
Details: These enclosures are designed to meet Mine Safety and Health Administration regulations, namely 30 CFR, Part 18. They should be able to contain an explosion within the enclosure without causing an external hazard to either personnel or the risk of causing further combustion.
Uses: They are mainly used in mining applications for equipment such as electric motor-driven mining gear, used in atmospheres containing methane or natural gas, with or without coal dust.
Conclusion
NEMA standards for hazardous locations mean enclosures can be built and rated for specific threats. These range from combustible vapors, gasses, and liquids to combustible dust and include ignitable materials. Each NEMA enclosure from 7-10 should also feature the letter of the group of hazardous materials they are rated against.
Combustion inside enclosures can lead to dangers to personnel, destruction of equipment, and fire, as well as the risk of this initial explosion igniting greater explosions in the environment outside the enclosure. Clear ratings and proper use are, therefore, absolutely critical for health and safety.
At Enercon, we have extensive experience designing and building enclosures for all environments, including the hazardous locations rated at NEMA 7-10. Whatever needs you have in terms of enclosures for your next project, we’ll be happy to help. You can contact us here.
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