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Fire Safety in Passenger Rail Transportation
From 1975 to 1979, rail transit car fire hazard evaluation reports for the Washington Metropolitan Area Transit Administration (WMATA) and Bay Area Rapid Transit District (BART) systems were published. The WMATA subway car fire evaluation consisted of individual small-scale tests of several interior materials and seven full-scale tests to determine the overall effects of an assembled system as compared to the fire characteristics of the individual components. The intent was to assist WMATA in assessing the potential fire hazard in new Metrorail subway cars. One criterion was that the ignition not spread from the area of origin. While the small-scale test results indicated that the car interior may not be readily ignited by very small ignition sources, the full-scale test results showed that the materials failed to perform in their end-use configuration as would have been predicted. For mock-up tests with urethane foam seat cushions, significant smoke obscuration was evident in approximately 5 minutes. Vinyl/chloroprene seat cushions were seen as less hazardous than an integral skin urethane foam assembly. The BART rail car evaluation included the review of interior and exterior car design, communication system, materials (tests and performance), fire detection and suppression, fire statistics, and scenarios. No tests were conducted. An additional study investigated fire safety guidelines for automated people movers systems. An extensive review of literature related to fire safety of fixed guideway transit systems was included in the report.
NIST studied the large-scale burning behavior of materials used for Amtrak passenger rail car interior furnishings. Small-scale cone calorimeter tests, and full-scale furniture calorimeter assembly tests were conducted. The comparison of small-scale flammability and smoke emission test data with real-scale test data showed that the small-scale tests were able to effectively quantify the effect of changes in materials within the same real-scale geometry. However, when the geometry of the full-scale rail coach car test mockup was changed, the chosen small-scale tests failed to predict the effects of the changes. Small-scale seat assemblies, and real-scale mock-up test data were compared. The relative fire performance of these materials (from lowest HRR to highest HRR) was consistent in mockup tests (for a given geometry of the full-scale mockup).
Beginning in the mid-1990's the U.S. Federal Railroad Administration (FRA) funded NIST to develop a systematic approach to the quantification of fire hazards in passenger trains that could form the basis for regulatory reform. At the time the research began the FRA issued guidelines that were generally utilized by the U.S. rail industry. During the work a major train accident in Silver Spring, Maryland occurred in 1996 that eventually resulted in the FRA guidelines being converted to federal regulations. An extensive literature review documented U.S. and European approaches to passenger train fire safety that rely primarily on individual small-scale test methods to evaluate material fire performance. This was followed by a three-phase research program. Phase I focused on the evaluation of passenger rail car interior furnishing materials using data from existing FRA-cited small-scale test methods and from an alternative test method using the cone calorimeter (ASTM International E-1354) . In Phase II, full-scale tests were conducted of selected interior material component assemblies using a larger scale furniture calorimeter; fire hazard analyses were then conducted for three types of intercity passenger rail cars, using data from both types of tests. Phase III compared the results of Phases I and II of the research program, with a series of full-scale fire tests conducted in an Amtrak coach rail car.
From the fire hazard analyses conducted, conditions in all three passenger rail car designs studied remain tenable sufficiently long enough to allow safe passenger and crew egress for all but the most severe ignition sources. Comparison of times to untenable conditions for a range of fire sizes determined from the full-scale experimental measurements with those calculated by the CFAST fire model showed agreement which averaged approximately 13 %. The range of ignition source strengths indicated that an ignition source size between 25 kW and approximately 200 kW is necessary to promote significant fire spread, which is consistent with the conclusions from earlier research that the ignition source strength of passenger rail car materials is 2 to 10 times greater than typical office furnishings.
NIST undertook a study undertaken to estimate the thermal environment of the Howard Street Tunnel in Baltimore, Maryland, following the derailment in July 2001 of a freight train and the burning of spilled tripropylene and the contents of surrounding rail cars. A numerical ﬁre model developed by BFRL was used to simulate the ﬁre’s growth and spread in the tunnel. The ﬁre model was been validated for this application using temperature data collected during a series of ﬁre experiments conducted at a decommissioned highway tunnel in West Virginia. The cross-sectional area of the tunnel and the ﬁre sizes used in the West Virginia experiments are similar to the Howard Street Tunnel.
For the Howard Street Tunnel ﬁre, the peak calculated temperatures within the tunnel were approximately 1,000 °C within the ﬂaming regions, and on average approximately 500 °C when averaged over a length of the tunnel equal to three to four rail car lengths. Because of the insulation provided by the thick brick walls of the tunnel, the calculated temperatures within a few car lengths of the ﬁre were relatively uniform, consistent with what one would expect to ﬁnd in an oven or furnace. The peak wall surface temperature reached about 800 °C where the ﬂames were directly impinging, and on average 400 °C over the length of three to four rail cars. The steel temperature of the rail cars would be expected to be similar to the surrounding gas temperature because of the long exposure time and the high thermal conductivity of steel.