Understanding Hazardous Locations According to NEC Hazard Codes

Posted by Power Temp Systems, Inc. on

NEC Hazard Codes

Power Temp Systems wants to enable people who work in potentially hazardous locations to get a better understanding of what is considered a hazardous location by the NEC and the proper precautions to take when bringing power into these types of areas. We will explore the different hazardous location classifications in the NEC to give you a better understanding of what to look for and what each tier in the system refers to.

The NEC uses the word “hazardous” as a way to define how a specific location is classified due to either the flammability properties in that area or the specific use of that area. Simply put, a hazardous location is an area where the possibility of an explosion, fire or electrocution exists, which can be created by the presence of flammable vapors, gases, moisture, combustible dust, or easily ignitable fibers.

NEC Classes

Classes define the general nature of the hazardous material that may be in the surrounding atmosphere. They are the first tier in the NEC classification systems. The NEC put flammability properties into classes. Each class represents different types of flammable materials or elements.

  • Class I refers to flammable gases or vapors that are or may be present in the atmosphere in significant enough quantities to produce a fire or explosion if ignited.
  • Class II refers to combustible or conductive dust particles that are or may be present in the atmosphere in significant enough quantities to produce a fire or explosion if ignited.
  • Class III refers to easily ignitable fibers or flyings that are or may be present in the surrounding area in quantities significant enough to produce a fire or explosion if ignited.

NEC Divisions

Divisions define the probability of a hazardous material or element being present in a surrounding atmosphere that has the ability to be ignited. They are the second tier in the NEC classification system and fall under classes. Divisions are broken into two levels that address all hazardous materials.

  • A Division 1 classification means that the substance in the Class it is paired with has a high probability of producing an ignitable or explosive mixture due to it being present continuously, intermittently or periodically. The substance may also come from the equipment in the area under normal circumstances.
  • A Division 2 classification means that the substance in the Class it is paired with has a low probability of producing an ignitable or explosive mixture due to it being present only during abnormal circumstances or for a short period of time, such as a system breakdown or container failure.

NEC Groups

Groups define the type of hazardous material in the area. Groups are broken out into seven different segments. The NEC lists and defines hazardous gases, vapors, and dusts by groups characterized by their combustible or ignitable properties.

  • Group A refers to an area that contains acetylene. If an area has this element present or there is a possibility it could be in the atmosphere, the area is considered hazardous.
  • Group B refers to an area that contains a flammable gas, liquid-produced vapor or combustible liquid-produced vapor mixed with air that has the potential to catch fire and burn or explode. The elements in this Group have an MESG (Maximum Experimental Safe Gap) value equal to or less than 0.45mm or an MIC (Minimum Igniting Current) ratio equal to or less than 0.40. Some examples include hydrogen, butadiene, ethylene oxide, propylene oxide, and acrolein.
  • Group C refers to an area containing a flammable gas, liquid-produced vapor or combustible liquid-produced vapor mixed with air that has the potential to catch fire and burn or explode. The elements in this Group have an MESG higher than 0.75mm or an MIC ratio between 0.40 and 0.80. Some examples include carbon monoxide, ether, hydrogen sulfide, morpholine, cyclopropane, ethyl, isoprene, acetaldehyde and ethylene.
  • Group D refers to an area containing a flammable gas, liquid-produced vapor or combustible liquid-produced vapor mixed with air that has the potential to catch fire and burn or explode. The elements in this Group have an MESG value higher than 0.75mm or an MIC ration higher than 0.80. Some examples include gasoline, acetone, ammonia, benzene, butane, ethanol, hexane, methanol, methane, vinyl chloride, natural gas, naphtha, and propane.
  • Group E refers to an area containing combustible metal dusts such as aluminum, magnesium, bronze, chromium, titanium, zinc and other commercial alloys.
  • Group F refers to an area containing dusts with carbon or carbon compounds, carbon black, coal black, charcoal, coal or coke dusts.
  • Group G refers to an area that contains combustible dusts that are not included in Groups E and F, such as flour, grain, sugar, wood, starch, chemicals, and plastics.

NEC Zones

Zones in the NEC classification systems define the properties of the hazardous material if it is a gas or a dust, and the probability of a hazardous material being present in the area in a form concentrated enough to ignite and start a fire.

  • Zones 0, 1 and 2 are reserved for gases, vapors, and mists.
  • Zone 0 refers to flammable gases or vapors that are present continuously or for long periods of time in ignitable concentrations.
  • Zone 1 refers to flammable gases or vapors that are present in ignitable concentrations that are likely to occur under normal operating conditions.
  • Zone 2 refers to flammable gases or vapors that are present in ignitable concentrations that are not likely to occur under normal operating conditions and are present for only a short period of time.
  • Zones 20, 21 and 22 refer to dusts, fibers or flyings.
  • Zone 20 refers to flammable dusts, fibers or flyings that are present continuously or for long periods of time in ignitable concentrations.
  • Zone 21 refers to flammable dusts, fibers or flyings that are present in ignitable concentrations that are likely to occur under normal operating conditions.
  • Zone 22 refers to flammable dusts, fibers or flyings that are present in ignitable concentrations that are not likely to occur under normal operating conditions and are

A simple solution for safer operations in questionable work environments is using quality equipment that is certified safe and efficient by industry-recognized organizations. Power Temp Systems carries a variety of UL certified equipment for all classifications of hazardous work areas. Our detailed product descriptions help operators understand why our products are so safe and why the help to create a safer work environment on any project. The main goal of our products is to distribute power in the safest and most efficient manner possible. We hope we could help you understand the risks of working in these types of environments and why it is crucial to take every precaution in any project involving electricity.