Understanding the Hazards of the Job
NFPA codes and standards define hazards differently.
NFPA Journal®, July/August 2008
NFPA codes and standards define a “hazard” using the perspective of the document’s purpose. There is no one definition for hazard or level of hazard because the common definition as a “potential for harm” is overshadowed by document-specific differences with regard to the potential of the kind of harm. When moving among documents, a user could be confused by the changes or, worse, not even notice the same words are used in different concepts and contexts.
For example, Section 18.104.22.168, Low Hazard Contents, of NFPA 101®, Life Safety Code®, defines low-hazard contents as those of “such low combustibility that no self-propagating fire therein can occur.” Section 22.214.171.124, Ordinary Hazard Contents, defines ordinary-hazard contents as those “that are likely to burn with moderate rapidity or to give off a considerable volume of smoke.” And Section 126.96.36.199, High Hazard Contents, defines high-hazard contents as those that “are likely to burn with extreme rapidity or from which explosions are likely.”
These definitions of hazard are based on the hazard to life safety and apply only to the contents, not the building structure. It is interesting to note that the low-hazard definition will apply to very few buildings as the phrase “no self-propagating fire therein can occur” excludes buildings with any combustible contents. A building storing salt for the state highway department may be an example.
NFPA 10, Portable Fire Extinguishers, uses a different definition for hazard that is based on the ability of someone using a portable fire extinguisher to extinguish a fire. For example, Section 188.8.131.52, Light (Low) Hazards, defines light (low) hazard occupancies as “locations where the quantity and combustibility of Class A combustibles and Class B flammables is low and fires with relatively low rates of heat release are expected. These occupancies consist of fire hazards having normally expected quantities of Class A combustible furnishings and/or the total anticipated quantity of Class B flammables present is expected to be less than 1 gal (3.8 L) in any room or area.”
This definition may leave one wondering what “low quantity and combustibility” is and how that may apply to a particular occupancy, but the Annex note provides several examples of low-hazard occupancies—another reason you should always read those Annex notes!
So the Life Safety Code would consider an office building an ordinary hazard, but NFPA 10 would consider it a light hazard for the placement of portable fire extinguishers.
NFPA 13, Installation of Sprinkler Systems, includes a different series of definitions of hazard in Chapter 5 that are based on the ability of sprinklers to control a fire, and other standards also have different definitions of hazard levels.
This complexity tells us this is an area that needs further development, and it is one for which we have the quantifying tools to make an important improvement.
For now, when discussing hazards, make sure that all parties involved understand the context or the code or standard in which the term is being used. The proper classification of hazard may be different within the same building or facility depending on which code or standard is being applied.
Chip Carson, P.E., is president of Carson Associates, Inc., a fire engineering and code consultancy. He is also a member of NFPA’s Board of Directors.