Technical Reports

Tank Car Relief Valve Requirement for Liquid Posison Inhalation Hazard (PIH) Lading

  • 01
  • Sep
  • 2003
AUTHOR: Peter Conlon, Milton R. Johnson, and Michael Grolmes
OFFICE: RPD
REPORT NUMBER: DOT/FRA/ORD-03/21
SUBJECT: Hazardous Materials
KEYWORDS: Tank Car, Hazardous Materials, Pressure Relief Valves, Poison Inhalation Hazard, PIH, Thermally Reactive Materials, Polymerizable Materials, Dangerous When Wet Materials
ABSTRACT: Analyses were performed for the Federal Railroad Administration (FRA) by Transportation Technology Center, Inc., a subsidiary of the Association of American Railroads, to determine if the changes made to Chapter 49 of the Code of Federal Regulations under docket HM-181 for the selection pressure relief valves used on tank cars transporting liquid materials designated as poison inhalation hazard (PIH) would affect safety. Also considered were the implications for other materials that are thermally reactive, polymerizable, or dangerous when wet. Key findings are: (1) The start-to-discharge pressure of a pressure relief valve on a tank car used to transport PIH materials is not a significant factor in the survival of the car when subjected to a 100-minute pool fire provided a large enough flow capacity is chosen for the valve; (2) If the overturned car case is included in the conditions to be considered by the regulations, it is recommended that the criterion for the pressure in the tank not exceeding the flow capacity of the valve not apply; (3) Although pressure relief design methods for polymerizable and thermally reactive materials are not considered in current regulations, surviving in a 100-minute fire is likely for most cases; (4) The relatively high start to discharge pressures used in present tank car safety relief devices are an impediment to achieving practical sized pressure relief for most runaway reaction scenarios.
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