Understanding how hazardous locations are classified can oftentimes seem a confusing and difficult process. With so many variances between the different hazards and dangerous materials that may exist, their frequency or duration of presence, and the differences in potential they hold for possible consequences, just figuring out the how’s and why’s of a locations classification can seem a daunting task. While we would like to be able to tell you that in reality the system of classification is actually simple to understand and apply, the truth is that some thought and consideration must be put into just how the classification is derived and applied in order to utilize it in practical applications. The following article outlines hazardous location standards as set forth in the National Electrical Code, or, NEC for short. The NEC deals with classification standards for the United States, however, the Canadian Electrical Code, or CEC for short, is also often applied to the same locations and equipment designed for operation within hazardous locations due to the great similarity between these codes. These code guidelines are generally accepted as valid in most instances between the United States and Canada and are almost identical in their makeup.

  
In the United States, OSHA is the government agency holding authority over workplace electrical safety and regulations, and in Canada it is the Standards Council of Canada. In both countries, local city, state and county or regions may also have their own added standards and regulations in addition to the standards noted above. It is the responsibility of operators, owners and those otherwise in charge of operating a facility to determine their locations’ classification and to meet compliance accordingly. Equipment to be used in hazardous locations must be approved for use in such locations according to classification and must have been tested by an (OSHA for the U.S. or SCC for Canada) authorized testing laboratory. Laboratories authorized by OSHA for the U.S. include Underwriters Laboratories (UL), MET Laboratories, and ETL Testing Laboratories Incorporated to name a few. In Canada, Underwriters Laboratories, C-UL Underwriters Laboratories of Canada, and the CSA Canadian Standards Association are some of the approved testing laboratories.

The National Electrical Code addresses hazardous locations in articles 500 through 516 and periodically adjusts these articles as standards are amended or altered. Hazardous locations are classified using NEC definitions, which also form the basis for testing of equipment to be used in hazardous areas. The following is a straightforward breakdown of hazardous locations and should be considered only a guideline. Operators should refer to NEC guidelines when dealing with their particular locations.

Class 1 locations are defined as areas where flammable gases or vapors may be present during the normal processes of operation in large enough quantities to create flammable or explosive mixtures and atmospheres.

Class 1 Division 1 locations are areas where a hazardous atmosphere can be present during normal operations. These conditions may be present continuously, occasionally, intermittently or periodically during normal operating, repair, servicing or maintenance operations. Additionally, this also includes areas where breakdowns or equipment failures release flammable or explosive vapors at the same time as an electrical equipment failure occurs.

Class 1 Division 2 locations are areas where flammable gases, liquids or vapors may be present under abnormal conditions such as during a container failure or accidental opening of a closed system. In these locations, gases and vapors are not normally present except within closed systems or in storage, but can become a hazard when they escape confinement and contaminate the ambient atmosphere.

Class 2 locations are areas where the presence of combustible dusts creates a hazardous condition. These dusts can consist of the shavings, flyings and finely divided particulates from a wide variety of materials including metals, wood, synthetics and plastics, each of which materials are covered under groups according to their explosive potential.

Class 2 Division 1 locations are areas where combustible dust may be present during the normal operating processes in large enough quantities and in suspension within the ambient atmosphere to produce an ignitable or explosive mixture. These dusts can be present constantly as a normal part of operations, introduced intermittently, or occasionally. These locations include conductive dusts and locations where failed or malfunctioning equipment can create a potential ignition source and create a hazardous location.

Class 2 Division 2 locations include areas where combustible dusts are not normally present in suspension, are not normally put into suspension, and or accumulations of dust can create interference with the normal heat dissipation of equipment or accumulations could be ignited due to their proximity to electrical equipment.

Class 3 locations denote areas where the presence of fibers and flyings present an easy potential for ignition and are in sufficient amounts to create a hazardous locations.  

 
Class 3 Division 1 locations are areas where the presence of flammable flyings and fibers are in high enough amounts to be easily ignited.

Class 3 Division 2 locations are areas where readily ignited flyings or fibers are stored and can present a hazard under abnormal conditions.

Classes and Divisions are also further broken up into groups. Groups denote the different types of materials, chemicals, gases, vapors and flammable liquids which may be present. Groups A, B, C and D denote flammable gases. Groups E, F and G denote combustible dusts. Materials are grouped according to their individual properties including their explosive force potential, ignition temperature, electrical conductivity, and composition.

Anyone considering the installation of electrical equipment into areas designated as hazardous locations must reference the National Electrical Code under sections 500 through 516 in order to ensure safety and compliance with all regulations on both federal and local levels. Local ordinances and regulations may differ from federal regulations and operators should make every effort to include all regulations into their installation schemes. Failure to comply with regulations can result in serious injuries or death as well as a loss of insurance and fines and penalties from regulating agencies charged with policing hazardous location compliance.