Looking for an opportunity to turn a basic concept into a controversial one on a project? Great! This week I'm exploring the quick-response remote area reduction that's provided in NFPA 13.
Suppress Early, Suppress Less
The concept behind reducing the calculated hydraulically remote area in a fire sprinkler system is entirely based on fighting a smaller fire earlier in the development of the fire.
There's a handful of factors that contribute to the timing of sprinkler response (a good future discussion), which include the thermal sensitivity, sprinkler temperature rating, distance of sprinklers relative to the ceiling, sprinkler spacing, ceiling height, and dynamics of the fire itself.
The reduction in the hydraulically remote area is based upon comparative tests of quick-response against standard-response spray sprinklers. According to the NFPA 13 handbook, the tests demonstrated that the earlier the water is applied to the fire, the smaller the fire and ultimately the less number of sprinklers needed to activate.
Not Universally Accepted
While the remote area reduction has been included in NFPA 13 for years, it's not universally accepted. Many engineer specifications don't allow the reduction, and design standards for major organizations such as the Department of Defense (UFC 3-600-01) don't permit it either.
Why not accept the remote area reduction, if NFPA 13 includes it? Like other elements in hydraulic design for fire sprinkler systems, not using the remote area reduction provides an additional safety factor to the system.
Additionally, since the quantity of sprinklers relates to the quantity of water flowing in the system, main sizes are directly impacted by using or not using the quick response area reduction. Building owners may opt to not want to reduce the remote area to preserve reasonable (larger) main sizes and give themselves flexibility on building modifications and sprinkler system changes in the future.
Quick-Response Area Reduction Calculator
This quick calculator is in part a checklist of prerequisites to reduce the remote area on a fire sprinkler system, in part a method of showing your work, and in part a quick calculator on determining your final remote area size. Don't see it below? Give it a try here.
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Joseph Meyer, PE, is a Fire Protection Engineer in St. Louis, Missouri. See bio on About page.