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Density for a 13-R fire sprinkler system

Density for a 13-R fire sprinkler system

Density for a 13-R fire sprinkler system

Just wondering, is it exceptable to use a density of .05 gpm to design for a NFPA 13R Light Hazard only? I am reviewing a set of plans and am not used to seeing that low of a density. Any comments would be helpful. Thanks.

RE: Density for a 13-R fire sprinkler system

Generally, in the dwelling units and ajoining corridors, you use the 0.05 or the listing of the head, whichever is greater.  Outside the dwelling units, you calculate per NFPA 13.

Travis Mack
MFP Design, LLC

RE: Density for a 13-R fire sprinkler system Residential Sprinklers that have been listed with specific coverage criteria.  Sprinklers shall be installed in accordance with the coverage criteria specified by the listing

Usually with residential you go by the cut sheets on the sprinklers and ensure they are spaced per listing and calculated as such.

The 0.05 is ok in garages per

If non-residential sprinklers are used then nfpa13r kicks it back to nfpa13 per

Hope this helps

RE: Density for a 13-R fire sprinkler system

I will be quickly corrected if I am wrong.

Depends on where you use them.

Saying light hazard I assume the area is outside the dwelling unit?  If it is the answer is no.  Inside dwelling units installed per 13R you are good to go with 0.05 but outside the dwelling units in 13R systems and everywhere in 13 systems, the minimum density of 0.10 must be met even when using residential sprinklers.

From NFPA #13 - 2002 Residential Sprinklers.* The design area shall be the area that includes the four hydraulically most demanding sprinklers.* Unless the requirements of are met, the minimum required discharge from each of the four hydraulically most demanding sprinklers shall be the greater of the following:  
(1) In accordance with minimum flow rates indicated in individual listings
(2) Calculated based on delivering a minimum of 0.1 gpm/ft2 (4.1 mm/min) over the design area in accordance with the provisions of  For modifications or additions to existing systems equipped with residential sprinklers, the listed discharge criteria less than 0.1 gpm/ft2 (4.1 mm/min) shall be permitted to be used.

Consider a 16'-3"x16'-3" living room in an apartment building designed per NFPA #13.

Using a VIKING VK466 sprinkler http://www.vikinggroupinc.com/databook/sprinklers/residential/091406.pdf this room would require 17.0 gpm and while you can use it in a 13 system or in a 13R system in a room measuring 16'-3" x 16'-3" the minimum discharge needs to be 26.4 gpm not the 17.0 gpm per listing.

If the room measured 16'-3" x 9'-0" (146.25 sq ft) to achieve the minimum density the sprinkler would discharge at 14.7 gpm but with a distance of 16'-3" you would need to use 17.0 which is in accordance with the listing.

99% of the time it doesn't impact but even in a 13R system once you are outside the dwelling unit the density of 0.10 gpm kicks in but we seldom see it because corridors are usually narrow enough where the issue doesn't come up.


RE: Density for a 13-R fire sprinkler system


Good analysis in your post.  You are correct that even at a 0.1 density, it often makes little difference in corridors and similar spaces becuase the spaces are narrow.  I also used to think that the 0.1 density applied outside the dwelling unit, even when using residential sprinklers.  But I recently had the opportunity to discuss the issue with an NFPA 13R committee member (informally, of course) and he pointed me to the last line of section of the 2002 edition of NFPA 13R:  "unless permitted by and" specifies densities, spacing requirements, etc. that all come from NFPA 13.  But section says that the listed spaces are to be protected in accordance with the requirements for residential sprinklers.  In NFPA 13R, that means a minimum density of 0.05.  Section does not reference requirements from NFPA 13.

The commentary from the sprinkler system handbook provides some additional insight in this case.  It points out that the reason residential sprinklers are allowed is that the fire hazard is very similar to those found in residential occupancies.  Hotel and motel lobbies are excluded because their fire hazard is no longer residential in nature.  

The person I spoke with indicated that as long as the fire hazard is considered similar enough to residential occupancies that residential heads can be used, there is no reason to treat the space any differently than a residence, and that includes the density.  He said the same reasoning applies in certain garages (section that are considered part of the dwelling unit.  That is why the density is allowed to be 0.05.


RE: Density for a 13-R fire sprinkler system


Deserves more checking on my part.

But I think I am right in saying residential sprinklers can be used in the dwelling units of systems that are designed per NFPA #13 but the density must be .10 gpm even inside the dwelling unit.  


RE: Density for a 13-R fire sprinkler system

Thanks for all the help. You guy's are great.

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