18 Oct Electrical Sources in Hazardous Locations

Electrical Sources in Hazardous Locations

Electrical equipment can become an ignition source when it produces sparks, arcs, or excessive heat in an atmosphere containing flammable gases, vapors, combustible dusts, or ignitable fibers. Proper electrical installations and equipment are essential for preventing fires and explosions in these areas.

Hazardous locations require specially designed and approved electrical equipment. Electrical components, wiring methods, and instruments must be suitable for the specific hazardous material and conditions that may be present.

Hazardous Location Classifications

Under the Class/Division system, hazardous locations are classified according to the type of combustible or flammable material present:

• Class I – Flammable Gases or Vapors: Locations where flammable gases or vapors may be present in quantities sufficient to produce explosive or ignitable mixtures.
• Class II – Combustible Dusts: Locations where combustible dust may be present in quantities sufficient to create a fire or explosion hazard.
• Class III – Ignitable Fibers or Flyings: Locations where easily ignitable fibers or flyings are handled, manufactured, or used.

Hazardous locations may also be designated as Division 1 or Division 2, depending on the likelihood and conditions under which the hazardous material may be present.

• Division 1 generally applies where hazardous concentrations may exist under normal operating conditions or may exist frequently because of maintenance, repair, leakage, or equipment failure.
• Division 2 generally applies where hazardous materials are normally contained within closed systems and hazardous concentrations are expected primarily under abnormal conditions, such as accidental rupture or equipment failure.

Selecting Electrical Equipment

Before selecting electrical equipment or wiring for a hazardous location, the hazardous area must be properly classified and the materials present must be identified.

Equipment suitable for one hazardous environment may not be suitable for another. For example, electrical equipment approved for combustible-dust locations may not be acceptable for an atmosphere containing flammable gases or vapors.

Electrical equipment must be approved for the specific Class, Division, material group, and operating conditions in which it will be used. Installation, inspection, and maintenance should be performed by qualified persons in accordance with applicable electrical requirements.

Explosionproof and Dust-Ignitionproof Equipment

Certain Class I locations require explosionproof equipment. Explosionproof enclosures are designed to withstand an internal explosion of specified gases or vapors and prevent the surrounding hazardous atmosphere from being ignited.

The term explosionproof does not mean the equipment cannot experience an internal explosion or that it is suitable for every hazardous location. Equipment must be specifically approved for the atmosphere in which it is installed.

Certain Class II locations may require dust-ignitionproof equipment. This equipment is designed to prevent combustible dust from entering the enclosure in quantities capable of interfering with operation or creating an ignition hazard and to prevent enclosure temperatures or internal ignition sources from igniting surrounding dust.

Examples of Hazardous Locations

Depending on the materials, processes, concentrations, and conditions involved, hazardous locations may include:

• Areas where volatile flammable liquids are transferred or dispensed.
• Interiors of spray booths and certain spray-finishing areas.
• Areas where flammable gases, vapors, or solvents may accumulate.
• Grain elevators and other areas where combustible dust may be suspended in the air.
• Fuel storage and gasoline-dispensing locations.
• Areas where ignitable fibers or flyings are manufactured, handled, or stored.

Safe Work Practices

Employees working in or around hazardous electrical locations should:

• Know the hazardous-location classification before beginning electrical work.
• Use only electrical equipment and wiring approved for the specific location.
• Never substitute ordinary electrical equipment for hazardous-location-rated equipment.
• Keep electrical enclosures, covers, seals, fittings, and fasteners properly installed.
• Inspect equipment for damage, corrosion, missing fasteners, damaged seals, and other defects.
• Maintain required grounding and bonding.
• Control static electricity and other potential ignition sources.
• Keep combustible dust from accumulating on electrical equipment and surrounding surfaces.
• Follow lockout/tagout procedures before servicing electrical equipment when required.
• Report damaged or improperly installed equipment immediately.

Remember

A piece of electrical equipment that is safe in an ordinary location may become an ignition source in a hazardous atmosphere. Know the classification, know the material creating the hazard, and use only electrical equipment approved for that specific environment.