Electrical Enclosures For Hazardous Locations: A Brief Guide For 2019

Explosions and fire are a major safety concern in the industrial plants. A number of engineering designs, codes, standards, and regulations emphasize this aspect of industrial safety, because of the grave and dangerous aspects of it. The Occupational Safety and Health Administration (OSHA) has a well-established system for classifying locations that are dangerous health hazards present in varying degrees at industries.

According to the OSHA Publication 3073, specially designed machine, equipment, and industrial panela, along with the special Installation techniques should be only used at the hazardous locations. These are the areas where flammable and combustible gases, vapors, liquids, and dust may be present, in quantity sufficient enough to cause fire or explosion.

What causes explosion or fire in an industrial setting

For an explosion/fire to occur, flammable substance or fuel, an oxidizer (or air), and a source of ignition (high heat or spark) should be present. The major causes of fire in the industry are listed below.

  • Combustion engine
  • Static electricity
  • Hazardous, impure and/or dirty chemicals
  • Defects in electrical wiring
  • Hot processes or work conditions
  • Mechanical spark
  • Improper employee training
  • Smoking on the premises
  • Improper supervision which leads to negligence of the codes and regulations pertaining to safety

The NFPA system of classification of hazardous location

The National Fire Protection Association (NFPA) has a system of classes, zones, and divisions through which it aims to classify the different kinds of hazardous locations. The classification is published in the NEC (National Electric Code) 70.

The division 1 areas are those industrial areas and processes where the flammable/gases/liquids or the ignitable fibers are manufactured, used, and handled. On the other hand, the division 2 areas are those where the flammable substances and vapors/gases are not used in the manufacturing processes but may be handled or stored in other areas. Class 1 areas contain the flammable vapors/gases, while the Class 2 areas contain combustible dust. The Class 3 areas contain ignitible dust, to an extent that it is risky.

Electrical Enclosures and their ratings

The use of correct equipment, including electrical enclosures and hazardous location panel, can prevent fire and explosion. The marking of the enclosure will provide information on the hazard group, class and protection type the enclosure conforms to. These ratings are given by NEMA (National Electrical Manufacturer Association. The UL (Underwriters Laboratories) rating may also show that the enclosure conforms to certain standards and can be used in specific areas.

Limiting the energy

Limiting the extent of energy (thermal or electrical) may reduce an essential element for an explosion or fire to occur. Fiber optics, pneumatics, and intrinsic safety may be used.

Isolation of the hazard

The method involves removing the hazard or preventing its diffusion or spread. Purge and pressurization systems and encapsulation, among other methods, can be used to attain the objectives.