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Hazardous Location Primer

This primer is meant to introduce some of the basic of hazardous (classified) locations as contained in Article 500 of the NEC (National Electric Code). It is meant for the non-professional and those who are “exposed” to these products but who do not have the time or resources for in depth study.

It is a fact that gases, vapors and mists escape during the production, processing, transporting and storage of flammable materials in the chemical and petrochemical industries, as well as in the production of mineral oil and natural gas, in mining and in many other sectors. Also, during many processes, flammable dust are created. These flammable gasses, vapors, mists and dusts, can form an explosive atmosphere. If this atmosphere is ignited, an explosion can take place, which may result in severe harm to human life and property

Electric powered lift trucks used in these areas must be designed to prevent any normal operation of the equipment from igniting the atmosphere.

NEC Hazardous Location Classification
A Hazardous Location is an area where a fire and/or explosion hazard may exist due to flammable gasses or vapors, flammable liquids, combustible dust, or ignitable fibers or flyings. The area is classified in accordance with properties of the material responsible for the potential hazard and with the likelihood of the hazard actually being present. The following explains the significance of Class, Group, and Division designators.

Class is used to provide a general definition of the physical characteristics of the hazardous material with which we are dealing. The three classes are:

Class I
Gasses, vapors and liquids that can be present in explosive or ignitable mixtures. For example: Gasoline – As a vapor (or liquid) is ignitable and/or explosive; therefore, it is a Class I material.

Class II
Dust. Combustible dust that can be present in amounts that could produce potentially explosive mixtures, or dust of an electrically conductive nature. Examples: Flour or cornstarch. As a compact mass these products may only burn or smolder but when finely distributed in air. The mixture becomes explosive.

Metallic dust such as aluminum or magnesium have several dangerous properties. They are electrically conductive. They can burn very violently even when not finely distributed in air. When finely distributed in air they can be violently explosive. All fall into Class II – Dust.

Class III
Fibers or flyings that are easily ignitable but are not apt to be suspended in air in such amounts to produce ignitable mixtures. Example: Rayon, Nylon, Cotton, Sawdust or Wood Chips, etc.

Groups
Group designations are used to selectively group the material by relatively similar hazardous characteristics. For Example: Both gasoline and hydrogen are explosive when mixed with and ignited, but the explosive effect and violence of the resulting explosion will be substantially different. Groups are designed by the letters A through G. Letters A through D are Groups for Class I and E through G are Groups for Class II.

A, B, C, D – Gasses/Vapors are grouped by:

  • Ignition temperature of the substand
  • Explosion pressure
  • Flammable characteristics

E, F, G – Dusts are grouped by:

  • Combustibility
  • Penetrability between parts
  • Ability to contribute to creation of an ignition source (abrasiveness, electrical conductiveness)
  • Blanketing effect
  • Ignition temperatures

Divisions
A Hazardous Location is an area where a fire and/or explosion hazard may exist due to flammable gasses or vapors, flammable liquids, combustible dust, or ignitable fibers or flyings. The area is classified in accordance with properties of the material responsible for the potential hazard and with the likelihood of the hazard actually being present. The following explains the significance of Class, Group, and Division designators.

Division 1
Division 1 locations which ignitable concentrations of flammable gases, vapors, liquids or combustible dust can exist all of the time under normal operating conditions.

Division 2
Division 2 locations which ignitable concentrations of flammable gases, vapors, liquids or combustible dust are not likely to exist under normal operating conditions.

Summary
Class: Denotes physical characteristics of the materials.
Group: Categorizes the materials by relatively similar hazardous characteristics.
Division: Classifies the likelihood of the presence of the hazardous condition.

RICO Equipment, Inc. cannot assume responsibility for Class, Group, Division or Operating Temperature determination. Ultimate responsibility is in the hands of user and authorities having jurisdiction.