Protective buildings located in hazardous areas must be designed to meet all ranges of area electrical classifications. Hazardous areas and locations are separated by class, division and group by NFPA 70: National Electric Code. These area locations are defined by the amount and type of various gases, vapors and other risk materials.
NFPA 70 recognizes three classes:
Class I – flammable gases and vapors
Class II – combustible dusts
Class III – easily ignitable fibers
In determining division, NFPA 70 recognizes two categories:
Division I - a location that is likely to have flammable liquid-produced vapors or combustible gases present under normal conditions
Division 2 - a location that is likely to have flammable liquid- produced vapors or combustible gases that can escape under abnormal conditions or in a case of accidental breakdown.
NFPA 70 also recognizes 5 major material groups that are determined by their flammability characteristics:
Group A- (ex. acetylene)
Group B- (ex. hydrogen)
Group C- (ex. ethylene)
Group D- (ex. propane, gasoline)
Group E-G- (ex. combustible dusts)
(For further information on flammable liquids and gases reference NFPA 497: Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas.)
Once the class, division and group has been identified there are number of NFPA-approved methods of providing protection techniques to meet the hazard. Methods to mitigate hazards include options ranging from providing classified electrical fixtures, to providing a pressurized building meeting NFPA 496, Standard for Purged and Pressurized Enclosures for Electrical Equipment. Depending on the owner’s safety policies, buildings may be equipped with gas detection sensors that activate alarms, shut down HVAC units and/or switch off the building’s electrical power.
For more specifics on MBI’s methods of addressing classified areas please contact us at +1 337-334-1900 and speak to one of our engineering specialists.
George Mayeux, Electrical Design Specialist