Occupational Safety And Health Administration OSHA

Date: 11/11/2013

Hazardous Classified Locations And National Electrical Code (NEC)

Construction Safety and Health Outreach Program

OSHA NEC Class Division Hazardous Classified Locations HMIThe National Electrical Code (NEC) defines hazardous locations as those areas "where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitable fibers or flyings."

A substantial part of the NEC is devoted to the discussion of hazardous locations. That's because electrical equipment can become a source of ignition in these volatile areas. Articles 500 through 504, and 510 through 517 provide classification and installation standards for the use of electrical equipment in these locations. The writers of the NEC developed a short-hand method of describing areas classified as hazardous locations. One of the purposes of this discussion is to explain this classification system. 

Hazardous Locations Definition

A Hazardous Location is an explosive atmosphere due to the presence of flammable gases, vapors, or liquids (Class I), combustible dusts (Class II) or ignitable fibers & flyings (Class III).

An area may also be considered "hazardous" for other reasons, such as the use of electrical equipment in the vicinity of water, the risk of personal injury from moving or falling parts, or even the presence of biological hazards. While hazards are associated with all of these conditions, areas are only considered hazardous (classified) locations under conditions defined by the NEC, CEC, IEC 60079-10, or CENELEC EN 60079-10, as applicable.

This approach to classifying hazardous locations is used by the United States (National Electrical Code), Canada (Canadian Electrical Code), Europe (CENELEC EN60079-10) and throughout the world (IEC 60079-10).

Hazardous Location Conditions

In addition to the types of hazardous locations, the National Electrical Code also concerns itself with the kinds of conditions under which these hazards are present. The Code specifies that hazardous material may exist in several different kinds of conditions which, for simplicity, can be described as, first, normal conditions, and, second, abnormal conditions.

In the normal condition, the hazard would be expected to be present in everyday production operations or during frequent repair and maintenance activity.

When the hazardous material is expected to be confined within closed containers or closed systems and will be present only through accidental rupture, breakage or unusual faulty operation, the situation could be called "abnormal."

The Code writers have designated these two kinds of conditions very simply, as Division 1 - normal and Division 2 - abnormal. Class I, Class II and Class III hazardous locations can be either Division 1 or Division 2.

Good examples of Class I, Division 1 locations would be the areas near open dome loading facilities or adjacent to relief valves in a petroleum refinery, because the hazardous material would be present during normal plant operations.

Closed storage drums containing flammable liquids in an inside storage room would not normally allow the hazardous vapors to escape into the atmosphere. But, what happens if one of the containers is leaking? You've got a Division 2 -abnormal - condition . . . a Class I, Division 2 hazardous location.

The three types of hazardous locations:

  • Class I - gas or vapor
  • Class II - dust, and
  • Class III - fibers and flyings.

And secondly, kinds of conditions:

  • Division 1 - normal conditions, and
  • Division 2 - abnormal conditions.

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CONTINUATION:

Hazardous Areas panel PCs AIS panel PCs and thin clients with HMI open platforms are designed and certified to meet National Electrical Code (NEC)/Canadian Electrical Code (CEC) Class/Division standards, ATEX Directive 94/9/EC Category 3, IECEx and IEC Zone standards for increased safety in Human Machine Interface (HMI) panels in Division 2 and Zone 2 applications. 

AIS offers UL Class I Division 2 (C1D2 or Class I Div 2), Groups A, B, C, D, T4, ATEX 94/9/EC Category 3 Zone 2, IEC’s IECEx Zone 2, Ex “nA” and Ex “ic” certification on its Hazardous Locations (Hazlocs) & Hazardous Areas panel PCs and open HMI platforms which are primarily designed for the volatile and harsh environments of Oil, Gas, and Petrochemical manufacturing industries. Learn more » 

The standard or custom HMI applications are designed to meet Class I and II, Division 2 and Class III, Divisions 1 and 2 Hazardous (Classified) Locations (North American Classification), and Zone 1/21 and 2/22 Hazardous Areas (European and IEC Classification) specifications.