IE Circular No. 78-18, UL Fire Test


                                                  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 


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. 


                                        Norman C. Moseley, Director 
                                        Division of Reactor Operations 
                                        Office of Inspection and Enforcement

1.  IE Circular No. 78-18
2.  Draft Transmittal Letter 

CONTACT:  D. C. Kirkpatrick, IE 

(Draft letter to all power reactor facilities with an operating license or a 
construction permit) 

                                                         IE Circular 78-18 

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. 

                                        (Regional Director) 

1.  IE Circular 78-18 
2.  List of IE Circulars 
      Issued in 1978 

                             UNITED STATES 
                         WASHINGTON, D. C. 20555  

                             November 6 ,1978 

                                                          IE Circular 78-18 



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. 


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. 

                                  1 of 3 

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 

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. 

                                  2 of 3 

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 

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 

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 

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. 

1.  Figure 1 
2.  Figure 2  

                                Page 3 of 3 

Page Last Reviewed/Updated Thursday, March 25, 2021