Burn Mode Analysis of Horizontal Cable Tray Fires (NUREG/CR-2431, SAND81-0079)
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Date Published: February 1982
Fritz R. Krause (Los Alamos National Laboratory)
Willard H. Schmidt
Systems Safety Technology Division
Sandia National Laboratories
Albuquerque, New Mexico 87185
Operated by Sandia Corporation
for the U.S. Department of Energy
Division of Engineering Technology
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
Under Memorandum of Understanding DOE 40-550-75
NRC FIN A-1010
Electrical cables constitute a serious fire hazard for nuclear power plants because the plastic insulation material is combustible and large quantities of cables are used in the plants. Nuclear power plant fires often continue to burn in the presence of smoke, whereas building fires usually burn in the presence of clear air, since smoke escapes through windows and doors before descending to the fuel. Fire growth classifications (realms) by the National Fire Protection Association (NFPA) thus may not be completely applicable for fire hazards analyses of nuclear power plants.
Electrical cable fire tests have been conducted at the Sandia Fire Research Facility in Albuquerque, New Mexico, in order to evaluate cable tray fire safety criteria for the Nuclear Regulatory Commission. A burn mode concept was developed in order to describe and classify the thermodynamic phenomena which occur in the presence of smoke and to compare the fire growth and recession of different cable types under otherwise unchanged fire test conditions. The importance of deep seated fires in cable trays from the standpoint of propagation, detection, and suppression is emphasized. The cable tray fire tests demonstrate that fire recession and deep seated fires can result from a descending smoke layer and that reignition and secondary fire growth is possible by readmission of fresh air.