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NFPA 75: Raised floor fire protection

Utilizing separate suppression 'zones' for both above floor and sub-floor spaces is a common practice in areas where the subfloor contains a significant hazard/fuel load.

We want your help for the following question about NFPA 75.Our company is designing a clean agent fire protection...

system for a data center. There are two rooms with false floor each, so the customer wants the system have four independent suppression zones in order to reduce the quantity of agent in a eventual discharge. It means one suppression system for each false floor and each computer room. Besides the tightness between false floor and computer room, what kind of considerations we must take? Are there some disadvantages or contradicting any standard?

Utilizing separate suppression 'zones' for both above floor and sub-floor spaces is a common practice in areas where the subfloor contains a significant hazard/fuel load.


  • Tightness between 'zones' is certainly one, as you have mentioned. The biggest concern here is likely not to be the physical tightness of the interlocking elements of the sub-floor, but rather the likelihood of designed ventilation (floor tiles with perforations or tiles left open under cabinets) used as part of the AC strategy. Make sure your fire suppression strategy synchronizes adequately with your AC strategy in this regard.
  • Generally speaking, use the same suppression agent for these two hazards. Although there is unlikely to be any major performance or health based issues with using different agents -- the NFPA 2001 standard does provide guidance in this area, section 1.8
  • Ensure that both zones of protection are adequately covered by independent fire and/or smoke detection means. This should also take into consideration the accessibility of these devices, particularly in the subfloor space. Service/maintenance of subfloor smoke detectors can frequently be problematic and is therefore sometimes (wrongly) neglected alltogether.
  • Ensure design and installation of the suppression system piping meets the equipment manufacturers specifications, particularly in the sub-floor space. This space can frequently be crowded with wiring and a challenge to install the piping correctly. Note things like nozzle types (sidewall or 360 degree), nozzle orientations (facing up or facing down) and t-split orientations to ensure they comply with the manufacturers specifications.

    Although a good local contractor will design and install correctly, there are many ways to cut corners in this challenging type of installation. Take the responsibility to double and triple check installation practices and design elements to ensure they meet with the manufacturers specifications.

This was last published in June 2006
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