IE Circular No. 78-18, UL Fire Test
CR78018
November 2, 1978
MEMORANDUM FOR: B. H. Grier, Director, Region I
J. P. O'Reilly, Director, Region II
J. G. Keppler, Director, Region III
K. V. Seyfrit, Director, Region IV
R. H. Engelken, Director, Region V
FROM: Norman C. Moseley, Director, ROI, IE
SUBJECT: IE CIRCULAR NO. 78-18, UL FIRE TEST
The subject document is transmitted for issuance on November 6, 1978. The
Circular should be issued to all power reactor facilities with an operating
license or a construction permit. Also enclosed is a draft copy of the
transmittal letter. This circular is being issued for information only. No
inspection followup is necessary since no action by the licensee is
requested. We anticipate sending a followup to this circular when the final
results of this fire test are available.
/s/
Norman C. Moseley, Director
Division of Reactor Operations
Inspection
Office of Inspection and Enforcement
Enclosures:
1. IE Circular No. 78-18
2. Draft Transmittal Letter
CONTACT: D. C. Kirkpatrick, IE
49-28180
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(Draft letter to all power reactor facilities with an operating license or a
construction permit)
IE Circular 78-18
Addressee:
The enclosed Circular 78-18 is forwarded to you for information. No specific
action is requested and no written response is required. If you desire
additional information regarding this matter, please contact this office.
Signature
(Regional Director)
Enclosure:
1. IE Circular 78-18
2. List of IE Circulars
Issued in 1978
.
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D. C. 20555
November 6 ,1978
IE Circular 78-18
UL FIRE TEST
Background
On September 15, 1978, a fire test of a full-scale vertical cable tray array
was conducted at the Underwriters Laboratory (UL) near Chicago, Illinois. It
was part of the fire protection research program managed by Sandia
Laboratories under NRC contract. The purpose of the test was to demonstrate
the effectiveness of area sprinklers and cable tray fire barriers
constructed Of ceramic fiber blankets in preventing damage to cables as a
result of an exposure to a flammable liquid fire. The test resulted in
damage to some electrical cables.
Discussion
The configuration of the fire test was selected to simulate a section of a
plant area with vertical cable trays containing redundant safety divisions
arranged such that the redundant divisions could be simultaneously exposed
to a potential fire resulting from an inadvertent spill of flammable liquid
in the area. The arrangement of the cable trays and the designation of the
redundant tray divisions is shown in Figure 1. Figure 2 shows the location
of the fire detectors and the three groups of sprinklers. Each of the five
cable trays contained cable insulated with polyvinyl chloride and Was
enclosed in a separated ceramic fiber blanket fire barrier from floor to
ceiling in accordance with the manufacturer's recommendations. The sprinkler
and detector arrangement was as permitted by NFPA Code. However, no water
vias actually used at any time during this test due to the failure of some
sprinkler heads to actuate, as explained below.
Each sprinkler location in the test arrangement contained three nominally
identical temperature sensing sprinkler heads with fusible links adjacent to
an open sprinkler head which was connected to a manual water supply valve.
The temperature sensing heads were wired to signal when their links fused.
After all three temperature sensing heads at a given location activated,
then the water supply for the open head was to be manually admitted. The
sprinklers were of a type which actuate at the slow end of acceptance for
reaction time. The test procedure required that all three temperature
sensing heads had to activate before water would be turned on. In this way,
it was expected to get some data on variability in the response time of
identical sprinklers.
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November 6, 1978 IE Circular 78-18
Test Details
The test was started by igniting the two gallons of heptane that was poured
into the floor pan. A fully developed fire occurred almost immediately. The
ceiling smoke detector alarmed in about 15 seconds. In about 50-60 seconds,
two of the three temperature sensing sprinklers located between the wall and
cable trays 1 and 2 activated. The fire between cable trays 1, 2, 3, and 4
appeared most intense, apparently because of a chimney effect between the
four trays. The flames between cable trays 3 and 5 did not appear to be so
intense. The ceramic fiber blanket absorbed some of the heptane so that
after the heptane in the pan burned, most of the flame seemed to come from
the bottom outside surface of the ceramic fiber blanket. No additional
temperature sensing sprinkler heads at any location activated; thus, the
sprinkler water supply was not turned on for any of the three sprinkler
locations. The apparent slow response of the third temperature sensing
sprinkler is being investigated, since this was not intended to be a slow
response sprinkler.
At about 3 minutes into the test there was an indication of a short circuit
in cable tray 3, which was probably caused by the fire. After 5-7 minutes
the height of the flames appeared to subside; however, residual flames
continued for about 40 minutes.
Preliminary Results and Analyses
Preliminary information indicates that the flammable liquid or flames
penetrated the protective barriers at the bottom of the vertical trays and
caused fire damage to the polyvinyl chloride insulation on cables in four of
the five trays.
On subsequent 500-volt megger tests, it was found that another cable in tray
2 had also experienced some damage, as evidenced by a conductor to ground
short.
The most probable cause of the fire damage in certain cable trays appears to
be related to the absorption or seepage of heptane under the ceramic fiber
blanket at the juncture with the floor. Once the heptane entered the
interior regions of the cable tray, then ignition apparently occurred via
the small opening at the floor or through a vapor/air path within the
joints. There is some indication that some cable damage was caused by
absorption of heptane on the inside of the barrier (wicking effect) and its
ignition which heated a cable tray ladder rung, causing damage to a cable in
contact with the rung. The ingress of the heptane into the ceramic fiber
needs to be further evaluated since this appears to be the most significant
failure mode.
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November 6, 1978 IE Circular 78-18
Tentative Conclusions
The test results are still being analyzed, and it would be premature to
establish firm conclusions at this time; however, the results now available
indicate that the following areas of the fire protection program need close
consideration:
1. To protect against spills of flammable liquids, barriers or curbs may
be needed to prevent entry of the flammable liquid behind fire
barriers. A wick effect may also need to be considered in the design of
fire barriers.
2. Some small fires may hot actuate sprinkler heads. To reduce this
possibility in sprinkler systems to be installed, fast response
sprinkler heads should be considered (less than approximately 3 minutes
in the UL Standard 199 "Automatic Sprinklers for Fire Protection
Service").
3. The location of the fire detection devices and the sprinkler heads
relative to the fire and components being protected is of great
importance. The path of the air movement in the area influences the
actuation of such devices and should be considered in the system
layout.
The final results of this test will be issued when the analysis of the test
is complete.
This circular is being issued for information only. No specific action is
requested and no written response is required. If you desire additional
information regarding this matter, contact the Director of the appropriate
NRC Regional Office.
Attachments:
1. Figure 1
2. Figure 2
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