American Fire Sprinkler Association
12750 Merit Dr., Suite 350 * Dallas TX 75251
Ph: (214) 349-5965 Fax: (214) 276-0908
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TECHNICAL UPDATE
OCTOBER 22, 2008
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"A self-storage facility has solid partition walls located more than
18 in. down from the deflector. Chain link fencing is applied from the
top of the wall up to the roof deck for security. Should the chain
link fencing be treated as an obstruction or wall?"
We have reviewed the 2007 edition of NFPA 13 as the applicable
Standard. Our informal interpretation is that chain link fencing is
not an obstruction and should not be treated as a wall.
NFPA 13 does not specifically address chain link fencing as an
obstruction or wall but we can gain clues from NFPA 13 on how to deal
with this application. First is the definition for unobstructed
construction where the structural members do not impede heat flow or
water distribution in a manner that materially affects the ability of
sprinklers to control or suppress a fire. In addition, the horizontal
structural members are not solid, where the openings are at least 70
percent of the cross section area and the depth of the member does not
exceed the least dimension of the openings. Annex material for bar
joist construction with fireproofing applied is considered obstructed
if the fireproofing is greater than 30 percent of the area (less than
70 percent open) of the joist in Section A.3.7.1 (7). Another area the
standard addresses a similar issue is privacy curtains in section
8.6.5.2.2.1 where the fabric mesh on ceiling tracks and have openings
in the mesh equal to 70 percent or greater and extend a minimum of 22
in. from ceiling shall not be considered obstructions. The handbook
commentary indicates that this applies to light hazard occupancies
only since the testing involved a light hazard environment. The
testing showed that as much water reached the opposite side of the
curtain as allowed by Section 8.6.5.2.2 for suspended or floor-mounted
vertical obstructions. In considering the self-storage application,
the solid walls are located more than 18 in. down from the deflector
and are not considered obstructions by NFPA 13. The sprinklers are
also spaced less than light hazard occupancies even though the fuel
package is higher for the storage. The chain link fencing located
above the wall is more than 70 percent open and will not impede heat
flow. Since the heat will readily flow to the ceiling, the next
question is will enough water get onto the floor area? We often think
that every inch of floor space must be directly wetted. This isn't
the case. As shown for obstructions greater than 18 in. below the
sprinkler, we can have obstructions up to 4 ft wide without sprinklers
beneath them. In addition, solid obstructions such as bookshelves in
libraries are acceptable as long as there is an 18-inch clearance.
This explicitly tells us that we can tolerate a fair amount of
shadowing on the floor and still maintain control of the fire. Thus
the chain link fencing installed above the wall is not an obstruction.
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Technical Update is prepared by the Technical Services Dept. of the
AFSA: Vice President of Engineering and Technical Services Roland
Huggins, a PE registered in fire protection engineering; Phill Brown,
a NICET IV certified automatic sprinkler technician and NFPA Certified
Fire Protection Specialist (CFPS) and Tom Wellen, a degreed fire
protection engineering technologist. This is provided with the
understanding that the AFSA assumes no liability for this opinion or
actions taken on it and they are not to be considered the official
position of the NFPA or its technical committees.
Copyright (c) 2008, American Fire Sprinkler Association. All Rights
Reserved
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