Differences in Laboratory Design Criteria Between NFPA and FM Global

written by Fire Protection Designer Alex Bielewicz

The design requirements of a sprinkler system can become complicated when FM Global sprinkler requirements need to be considered in addition to the typical requirements of NFPA 13 – Standard for the Installation of Sprinkler Systems. Sometimes these two organizations classify the hazard of an occupancy in different ways. NFPA 13 uses light hazard, ordinary hazard (group 1 or 2), and extra hazard (group 1 or 2). FM Global data sheet 3-26 uses hazard category 1, hazard category 2, and hazard category 3. A difference in occupancy classification can mean very different requirements for the size of the hydraulic calculation area and the amount of water needed to discharge per sprinkler. This can change the number of sprinklers, type of sprinkler, and pipe size – all things that can have a significant cost implication.

One example of an occupancy type with conflicting classifications is laboratory spaces. NFPA 45 – Standard on Fire Protection for Laboratories Using Chemicals divides labs into class A, B, C, or D. Class A or B laboratories are designed to NFPA 13 ordinary hazard group 2, while Class C or D laboratories are designed to NFPA 13 ordinary hazard group 1. FM global considers laboratories to be hazard category 1, in both healthcare or chemical and pharmaceutical settings. In this case, NFPA 13 has the stricter design requirements – a density of 0.15 gpm/ft² for OH1 or 0.20 gpm/ft² for OH2 over a minimum calculation area of 1500 ft². FM’s requirements are a density of 0.10 gpm/ft², also over a minimum calculation area of 1500 ft².

In a situation like this, you have to consider what the authority having jurisdiction (AHJ) will require when reviewing the plans and calculations. The local or state fire marshal will require the design to at the very least meet the NFPA requirements for sprinkler systems. With a laboratory space, that means designing to a hazard classification of ordinary hazard group 1, even though FM Global sprinkler requirements are less strict. On the other hand, in an occupancy where FM’s recommendations are stricter than the requirements on NFPA 13, the system should be designed for FM Global sprinkler requirements.

In addition to the typical design requirements for laboratories of NFPA 13 and FM Global (data sheets 2-0 and 3-26), there are other NFPA standards or FM data sheets that may need to be consulted for protection of higher hazard materials in the labs. NFPA 45 only allows for certain quantities of flammable chemicals to be used and stored in a laboratory, while NFPA 30 – Flammable and Combustible Liquids Code contains requirements for larger quantities of chemical storage.

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