Here here. We witness the very same problem on large wet gridded systems,
just as your experience and research indicates.
We have one AHJ would REQUIRES test/drain ITCs. Guess where my false
alarming issues are? I suspect this AHJ requirement is for their
convenience and is not based on scientific laws of hydraulics and certainly
not based on NFPA recommendations or typical trade practice. We have to
live with the unintended consequences as a result of this "design
compromise/requirement".
Byron
Byron Blake, CET
Service/Inspections
Freedom Fire Protection, LLC
Longmont, CO
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Rodney Hamm
Sent: Sunday, March 01, 2009 5:38 PM
To: [email protected]
Subject: RE: statistics
If anyone has any pull or influence with the development of NFPA 13........
Please discuss the idiotic approach of installing Inspector's Test
Connections at the sprinkler riser (~12 in. downstream of the flow switch).
This has been considered "acceptable" by NFPA 13 since 2002 and is quickly
becoming standard practice in the great state of Georgia. There are several
significant reasons why this is a bad idea AND from an engineering
standpoint this is a very poor design. The inevitable trapped air in the
system causes or can potentially cause a number of problems: Excessive
system pressure when temperatures increase, false water flow alarms due to
air pocket expansion/contraction, failed water flow alarms due to cycling
flow switches, increased rust on the interior surfaces of sprinkler piping,
etc.
From what I have seen, most contractors or sprinkler designers who
primarily
install or design new systems have no idea this approach causes problems for
the building owner and/or fire protection system inspectors. I can confirm
these are common problems at several of the facilities I have visited over
the past few years. In many instances, the only effective solution is to
install a suitably located Inspector's Test Connection or bleed the air
pockets using sprinklers at the highest elevations. We have installed air
bleed off connections for numerous systems simply to allow trapped air to be
removed from the high point. The problem is access at some facilities after
the solid ceilings or other obstructions have been introduced.
In my humble opinion, Inspector's Test Connections should be installed at
the most remote point of each system. The connection point (prior to being
piped to within 6 ft. of the floor level) should be at the highest elevation
of the sprinkler system piping whenever possible. Auxiliary drains or low
point drains should NOT be considered Inspector's Test Connections.
I would assume it is safe to say anyone who has enough experience and
personal dealings with inspections and/or problem solving (after the design
phase and initial installation project has been completed) realizes that the
Inspector's Test Connection serves more purposes than just testing the water
flow alarms. {I have heard "the sole purpose of the ITC is to test the alarm
device" so many times that I get a smile every time someone spouts it.} I
simply disagree with the relatively recent change in NFPA 13 which allows
this approach. I strongly believe the practice of installing the Inspector's
Test Connection a few feet downstream of the water flow switch should be
considered unacceptable.
In many instances, the fire alarm companies and building owners have to deal
with the issues caused by this poor design. They rarely if ever realize the
true source or reason for the intermittent false alarms. They simple bypass
the alarm or set the delays so high that flow switch cycling becomes a
problem during alarm testing.
We see systems with >175 psi on a regular basis caused by this
problem.......some systems even peg the 300 psi gauges. On of my customers
had 5 separate incidents where sprinklers developed leaks and/or popped open
due to excess system pressure during Spring & early Summer of 2007. We added
pressure relief valves in August of 2007 for all of their wet systems and
this resolved the problem. This is a >1 million sq. ft. facility with
several wet systems. False fire alarms and excess air pressure are very
common problems when the ITC is not located at the most remote and/or
highest elevation of the system piping. I could provide many more examples,
but I think I have made my point.
Black steel, moisture and trapped air allows more rust to develop on the
interior surfaces of the sprinkler piping than if the majority of the
sprinkler piping is full of water. Therefore, it would be safe to conclude
that trapped air in the sprinkler systems will shorten the life of the
sprinkler system piping.
The fact that someone or some group convinced the NFPA committee to change
the standard and the fact that the approach saves time and money during
installation does not make it a good engineering design!
There are probably a few instances where placing the ITC a few feet
downstream of the flow switch should be considered acceptable due to limited
or no feasible alternatives; however, these instances should be the last
resort alternative rather than standard practice.
Just one man's perspective!! I wonder if anyone on this forum agrees with me
on this subject.
Rodney K. Hamm, P.E.
President/Owner
Falcon Fire Protection
Office (478) 953-1677
Cell (478) 396-6988
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