AMERICAN FIRE SPRINKLER ASSOCIATION
12750 Merit Drive, Suite 350 * Dallas, Texas 75251
Ph: (214) 349-5965 Fax: (214) 276-0908
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TECH TALK
June 2007
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OBSTRUCTED OR UNOBSTRUCTED CONSTRUCTION
What do you classify a standard wood truss with 2x6 top cords but in
addition to this one another 2x6 was sistered to the top cord so that
the top cord measures 11 in. deep? Per NFPA 13, truss construction
is considered unobstructed. Is a truss even with one 2x6 top cord
considered unobstructed when a joist that is a 2x6 is considered
obstructed? What's the difference? This question hits the nail on
the head. It does NOT matter what you call the structural member but
as the definition says, whether or not the member impedes heat flow.
If the top chord is deep enough to be readily identified as
obstructed when it is a joist then it IS obstructed construction.
The root cause of our problem is that there is nothing that
quantifies how deep is too deep for unobstructed. We attempted to
get this straightened out in the 99 edition and the TC response was
that it is defined in the Annex. When we pointed out with a comment
what the Annex quantities and it isn't depth DOWN from the ceiling
the TC still elected to ignore it. You can lead a horse to water but
you can't make it drink. The annex identifies 4 inches deep as part
of what differentiates a joist from a beam (rightly called thickness
and width in this section) and a bar joist from a truss (called depth
in this section) but it is the distance ACROSS the structural member
as clearly identified in Figure A.3.7.2(c). Nothing discusses
distance down from the ceiling.
Few would call a 2x6 joist unobstructed but what about a 2x4
stringer? As a reasonable point of demarcation, we use the 2x4.
Looking at the figures in the annex of a Truss, it looks like a 2x4.
We know some amount of protrusion is acceptable and a 2x6 joist is
generally accepted as obstruction so WALLAH, a 2x4 is unobstructed
and anything beyond it REGARDLESS of the name of the member is
obstructed (assuming the spacing is as defined of course).
SPRIG OR SPRIG-UP?
Sprigs or sprig-ups were addressed during the 2006 ROP/ROC process.
What's the difference? None. The term was used interchangeably in
the 2002 edition and the submitter wanted to clean up the language in
the standard and the committee agreed. A change was made to use the
term "sprig" from "sprig-up" and the definition remains the same as
"A pipe that rises vertically and supplies a single sprinkler."
The bigger issue is installation of sprigs where the committee copied
section 9.3.6.5 (seismic requirement for restraint of sprigs) and
created a new Section 9.2.3.7 "Sprigs 4 ft (1.2m) or longer shall be
restrained against lateral movement." The change addresses the
concerns raised by the Hanging and Bracing Committee for the pipe to
remain in place as intended. The committee felt that long sprigs
required restraint to ensure that the sprinkler remained in its
intended location during the life of the system and when flowing.
Another proposal that was REJECTED was section 8.3.1.3 Upright
sprinklers installed on sprigs less than 12 in. shall be installed
with the frame arms parallel to the branch line or main, unless
specifically listed for other orientation. The submitter indicated
that sprinklers installed on mains may cause shadowing but the
committee determined there was insufficient data to back this
proposal. Section 8.6.5.2.1.8 addresses upright sprinklers on piping
that the 3 times rule doesn't apply if the piping is less than 3 in.
MARK YOUR CALENDARS FOR THE NEXT VIRTUAL SEMINAR
Commissioning
July 11, 2007
To Register:
Event ID: 12912
12:00 PM EDT
11:00 AM CDT
10:00 AM MDT
9:00 AM PDT
Earn: 0.1 CEU's / 1.0 CPD's.
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Non Member: $130 per connection
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To Register:
By Phone: 800-775-7654, please have your credit card information ready.
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54702-1187 (Payment must accompany registration)
Online: www.krm.com/afsa
UPCOMING CENTER FOR LIFE SAFETY EDUCATION (CLSE) VIRTUAL SEMINAR
Residential Sprinkler Update
August 22, 2007
Event ID: 12913
SAVE THE DATE! Seminar and Registration details coming soon.
2007 AFSA DESIGN SCHOOLS
Beginning System Planning School
July 9-20, 2007 Sold Out!
August 6-17, 2007 Sold Out!
October 8-19, 2007 Sold Out!
November 5-16, 2007 Sold Out!
December 3-14, 2007
Registration Prices:
Member $1200
Non-Member $1700
TechTalk is prepared by the Technical Services Department of the
American Fire Sprinkler Association: Vice President of Engineering
and Technical Services, Roland Huggins, a PE
registered in fire protection engineering; Phill Brown, a CFPS and a
NICET IV certified automatic sprinkler technician, and Tom Wellen, a
degreed fire protection-engineering technologist. Opinions are
provided with the understanding that AFSA assumes no liability for
the opinions or actions taken on them and they are not to be
considered the official interpretation of the NFPA or that of its
technical committees.
Copyright (c) 2007, American Fire Sprinkler Association, 9696
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