Due to our large distribution center market segment, we see a lot of water tanks each year. Recently our engineers have been specifying tanks to be heated and insulated in areas where it was not required in the past. We have received strong pushback from general contractors and sprinkler contractors. Often the response we get in these situations is “We have never done that before!”

The common denominator is the client’s desire to comply with FM Global requirements. In the July 2022 edition of Factory Mutual Data Sheet (FMDS) 3-2 Water Tanks for Fire Protection, there was an important change in the requirement for heating of water tanks compared to the previous edition. In fact, there has been an evolution in the heating requirement in both FMDS 3-2 and NFPA 22 Standard for Water Tanks for Fire Protection.

Beginning in 2018 NFPA 22 and 2022 FMDS 3-2 both removed the isothermal maps from the body of the standard. However, the FMDS now contains a link to a more detailed online map.

NFPA 22 Table 16.2.1(a) requires a heating system for an on-grade suction tank when the lowest one-day mean temperature (“LODMT”) is <5°F (-15°C). The temperature information is to come from an approved source as required by TIA 18-1 issued August 14, 2018. Determining what source will be approved may be a challenge.

Prior to July 2022, FMDS 3-2 required a heating system for an on-grade suction tank based on the LODMT and when available the 30°F normal daily minimum temperature (“NDMT”). Heat (and thermal insulation) was required for a pump suction tank when the LODMT is ≤5°F (-15°C). However, heat (and insulation) was required for exposed piping for suction tanks when the LODMT is ≤15°F (-9.4°C) and insulation for exposed piping for suction tanks when the LODMT is ≤20°F (-6.7°C).

The requirements of FMDS 3-2 have been updated and are now based on the 100-year daily minimum temperature (“100-year DMT”). Heat (and thermal insulation) for a pump suction tank is required when the 100-year DMT is ≤-5°F (-20.6°C). However, heat (and thermal insulation) is required for exposed piping for suction tanks when the 100-year DMT is ≤5°F (-15°C) and insulation for exposed piping for suction tanks when the 100-year DMT is ≤20°F (-6.7°C).

The result of the change in the basis for pump suction tank heat in FMDS 3-2 is that locations such as: Portland, Little Rock, Memphis, Nashville, Birmingham, Atlanta, Greenville/Spartanburg, and Raleigh/Durham, will now require heat and thermal insulation for fire pump suction tanks when insured by FM Global. The 100-year DMT map is available at FMGlobal’s website by selecting the Natural Hazard Maps button and then selecting the freeze map.

Many clients prefer to follow the recommendations of the various FM Data Sheets even if they are not insured by FM Global. We recommend that non-FM Global insured clients contact their insurer and determine if a pump suction tank designed and installed in accordance with NFPA 22 is acceptable.

Imagine saving your client $100,000 with one phone call!