Hazard Area Classification, HAC

Hazardous Area Classification, HAC, or zoning is the discipline used to define where and how often a flammable atmosphere may exist. In order to carry out a risk assessment for combustible dusts with respect to fire and explosion it is necessary first to identify where flammable clouds or layers could be present.

Combustible Dust

According to NFPA 499 and NFPA 70, Locations shall be classified on the basis of the properties of the combustible dust or ignitable fibers/flyings that may be present, and the likelihood that a combustible or combustible concentration or quantity is present.

Class II, Division 1. Broadly equivalent to zone 20, 21

  • In which combustible dust is in the air under normal operating conditions in quantities sufficient to produce explosive or ignitible mixtures, or
  • Where mechanical failure or abnormal operation of machinery or equipment might cause such explosive or ignitible mixtures to be produced, and might also provide a source of ignition through simultaneous failure of electric equipment, through operation of protection devices, or from other causes

Class II, Division 2. Broadly equivalent to zone 22

  • In which combustible dust due to abnormal operations may be present in the air in quantities sufficient to produce explosive or ignitible mixtures; or
  • Where combustible dust accumulations are present but are normally insufficient to interfere with the normal operation of electrical equipment or other apparatus, but could as a result of infrequent malfunctioning of handling or processing equipment become suspended in the air;

Detail methodology used for HAC Combustible Dust according to NFPA 499 is shown at Figure 1. Data required for HAC Combustible Dust is shown at Table 1

Figure 1 Methodology HAC Combustible Dust According To NFPA 499
Table 1 Data Required for HAC Combustible Dust

Flammable Liquid/Gas

According to NFPA 497, the decision to classify an area as hazardous is based on the possibility that an ignitible mixture could occur. Having decided that an area should be classified, the next step is to determine which classification methodology should be utilized: the U.S. traditional NEC Articles 500 and 501, Class, Division, Group; or the NEC Article 505, Class, Zone, Group. 

This proposal is to seek study according to Class, Division, Group for Hazard Area Classification according to NFPA 497 as follow: 

  • Division 1 Classified Locations, broadly equivalent to Zone 0/1. A condition for Division 1 is whether the location is likely to have an ignitible mixture present under normal conditions. For instance, the presence of a combustible material in the immediate vicinity of an open dip tank is normal and requires a Division 1 classification.
  • Division 2 Classified Locations, broadly equivalent to Zone 2. The criterion for a Division 2 location is whether the location is likely to have ignitible mixtures present only under abnormal conditions. The term abnormal is used here in a limited sense and does not include a major catastrophe.

Detail methodology used for HAC Flammable liquid/gas according to NFPA 497 is shown at Figure 2. Data required for HAC Flammable Liquid/Gas is shown at Table 2.

Figure 1 Methodology HAC Combustible Dust According To NFPA 499
Table 2 Data Required for Extent HAC for Flammable Liquid/Gas