Smoke and Heat detector covering area
- Thread starter TMMB
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gadfly56
Senior Member
- Location
- New Jersey
- Occupation
- Professional Engineer, Fire & Life Safety
Unless they have a specific listing, smoke detectors can be assumed to cover a 30' x 30' area. Technically, it's a circle with a radius of 21', which the 30' x 30' square just fits inside. Configuration of the ceiling may reduce the allowed spacing (beams, eg). There is no height limitation in the code, but for tall spaces (atriums, eg) you must consider stratification. As the smoke plume rises, it cools. At some point the smoke may collect in a layer that is below the ceiling of the space and of course the detectors won't see the smoke. Beam detectors are often used in this application.
Heat detectors similarly default to 30' x 30' coverage, but are more likely to have an actual listed spacing. They may have different listings for UL and FM, 25' for one and 50' for the other for example. Heat detectors are de-rated for height, but not to less than 40% of their listed spacing; see NFPA 72 for a table.
copper chopper
Senior Member
- Location
- wisconsin
according to the latest nfpa 72 every manufacturer does there own testing and sets there different spacing and hieght requirements so its up to what ever the manufacturer recomends.If your local fire marshall is a hardhead about this, he will want to see the instructions from them or he already knows... you can contanct the maker of your product and tell them what your situation is to ask for an application of there product.... and get it in wrighting...
gadfly56
Senior Member
- Location
- New Jersey
- Occupation
- Professional Engineer, Fire & Life Safety
I don't see any substantial difference between the 2010 and 2007 editions. The use of the 30-foot rule etc, still applies. Can you provide specific examples?
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