Michael,
The following is the logic used in a project that we work with the Owner in
addressing the AHJ concerns. THIS IS FOR YOUR REVIEW AND NOT FOR USE IN DESIGN,
SINCE THIS IS AN ENGINEERING OPINION AND I AM NOT PROVIDING AN ENGINEERING
OPINION IN MY RESPONSE TO YOUR QUESTION.
The logic of looking at similar fuel load and fuel load configurations in NFPA
13 in order to apply to the PODS unit storage being contemplated is a common
practice in the fire protection engineering community.
Let us look first at the type of commodity being stored in the PODS unit.
Discussion with other AHJ Fire Protection Engineers the commodity
classification of the storage within the PODS units. The Fire Protection
Engineer stated that he had opened and inspected a large number of the PODS
units through out his jurisdiction and classifies the storage to be typical
Class IV commodity. NFPA 13 Paragraph 2-2.3.4 defines a Class IV commodity as
a product, with or without pallets, that meets one of the following criteria:
(1) Constructed partially or totally of Group B plastics.
(2) Consists of free-flowing Group A plastic materials.
(3) Contains within itself or its packaging an appreciable amount (5
percent to 15 percent by weight or 5 percent to 25 percent by volume) of Group
A plastics. The remaining materials shall be permitted to be metal, wood,
paper, natural or synthetic fibers, or Group B or Group C plastics.
The NFPA definition of a Class IV commodity describes almost all house hold
products that could be stored in a PODS unit.
Now that we have defined the type of commodity lets look at the height and
storage configuration of the fuel load.
The PODS unit is enclosed on five sides with ¾ inch plywood panels supported by
4" x 4" wood framing, approximately 8' wide x 8'-5" high x 16' long with a
flexible plastic roof. A fire in a PODS unit will grow within the unit, when
the roof of the unit is breached by the fire a large amount of heat and
unburned products of combustion will be released into the building, which can
result in a large column of superheated air racing to the ceil of the building.
This large heat release from a shielded fire will overwhelm an ESFR sprinkler
system by operating an excessive number of sprinkler heads. Each three high set
of stored units with have a minimum 3 ft access aisle on all four sides of each
stack of three high PODS units.
To overcome the heat release from a shielded fire 286ºF temperature rated
standard type of sprinkler will need to be used in the sprinkler system.
Historically, this sprinkler head was used to address high heat release rated
fires.
A similar occupancy that has a shielded fire growth potential is the
manufacturer of mobile /modular homes which is classified as an Extra Hazard
Group II occupancy classification which is required to be protected by a
sprinkler system designed to provide a design density of 0.40 gpm per sq. ft.
over the hydraulically most remote 2,000 sq. ft. using 286ºF temperature rated
sprinklers at the ceiling.
A second design criterion is defined using the fire control approach for
commodities stored on pallets, in solid piles or in bin boxes. The storage of
Class IV commodity to a height of 25'-6" on pallets, in solid piles or in bin
boxes required to be protected by a sprinkler system designed to provide a
design density of 0.426 gpm per sq. ft. over the hydraulically most remote
2,000 sq. ft. using 286ºF temperature rated sprinklers at the ceiling.
It appears that both design criterions are converging to a design density of
0.426 gpm per sq. ft. over the hydraulically most remote 2,000 sq. ft. as a
single design point.
Because of the storage of the PODS units three high there is a real possibility
that a fire in a lower unit will cause the collapse of the pile onto a second
pile of storage units and at the same time shield the fire from the water
discharge from the overhead sprinkler system. In order to address the shielded
fire issue from a collapse of a pile of three storage units a second sprinkler
system density design criteria needs to be provided. Usually when there is a
concern about a shielded fire the area of operation for the sprinkler system is
increased to either 4,000 sq. ft. or even as high as 5,000 sq. ft. with a
minimum design density of 0.30 gpm over the hydraulic most remote area. The
design density of 0.30 gpm provides protection of the building's steel roof
structure from the heat released from the shielded fire.
We recommended a design criteria as to produce a sprinkler system density of
0.42 gpm per sq. ft. over the hydraulically most remote 3,000 sq. ft. and a
secondary design density of 0.30 gpm per sq. ft. over the hydraulically most
remote 4,000 sq. ft.
A report was on how the design criteria was developed and sent to the AHJ for
their review. This is an extremely condensed version of the engineering report
sent to the Owner and AHJ.
Have a fire safe day.
Jim
DAVIDSON ASSOCIATES
Fire Protection Engineering P. O. Box 4010
Code Consultants Greenville, DE 19807-0010
Medical Gas Systems Engineering (302) 994-9500
Fax (302) 234-1781
CONFIDENTIALITY
This report and any attachments are confidential and also may be privileged.
If you are not the named recipient, or have otherwise received this report in
error, please destroy the report, notify the sender immediately, and do not
disclose its contents to any other person, use them for any purpose, or store
or copy them in any medium.
Thank you for your cooperation.
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Michael
Foster
Sent: Friday, July 05, 2013 2:46 PM
To: [email protected]
Subject: POD Storage
We have a client that wishes to store the POD style storage units in their
warehouse, they have asked what sprinkler design criteria is required. I have
been unable to fine anything in NFPA or FM data sheet, so I am looking for any
help
Thanking you in advance
Regards
Michael Foster
Phaser Fire Protection Ltd.
[email protected] <mailto:[email protected]>
tel: 604.888.0318
fax: 604.888.4732
cel: 604.790.0937
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