ETL 1110-3-481
31 Mar 97
release stations. These systems have open orifices. The worst
case for open systems is an accidental discharge, and the fire
department responding and shutting off the system. Containment
will be designed to hold a minimum of 10-minutes of full system
flow. This capacity should be increased if longer fire
department response times are anticipated.
e. Closed Fire Extinguishing Systems. Closed systems are
systems which have no open orifices. In order for these systems
to discharge, there must be a fire that produces sufficient heat
to fuse sprinkler heads. Such systems are overhead wet-pipe
sprinkler systems and pre-action sprinkler systems. For these
systems, the worst case is defined as the discharge that occurs
from periodic testing. Containment systems will be designed to
hold 3-minute test flows of each system and to facilitate
required periodic flow testing.
Containment System Capacity
5.2
The minimum capacity of any containment system should be adequate
to handle anticipated maximum flows. For open fire extinguishing
systems, the capacity should be based upon the one event that can
produce the largest single discharge amount from an inadvertent
activation. For closed fire extinguishing systems, the
anticipated flow is that produced during acceptance and periodic
system testing.
5.2.1
Discharge From Open Systems
Containment capacity must consider both inadvertent discharges
from open discharge devices, e.g., nozzle systems, as well as
discharges from testing of all system proportioners. Capacity
should be based on a discharge duration of 10 minutes due to
inadvertent discharge from open discharge devices. For example,
assume an aircraft hangar has three closed-head sprinkler
systems, each with a design flow rate of 2,400 gpm, and a nozzle
system with a total calculated flow rate of 2,200 gpm. The
required containment capacity for an anticipated 10-minute
inadvertent discharge of the nozzles would be 22,000 gallons. A
22,000 gallon capacity containment system would be more than
adequate to handle a 3-minute test flow of 7,200 gallons of foam
solution from a single proportioner. In actuality, the
containment system could handle the test flows from three of the
four closed-head sprinkler systems. The ten minute duration for
inadvertent flows may be modified, if the designer determines
that the emergency response to shut the AFFF systems would either
take more or less time than 10 minutes.
A-8
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