Technical Reports

A Study to Reduce the Hazards of Tank Car Transportation

  • 01
  • Nov
  • 1970
AUTHOR: Bullerdiek, Vassallo, Adams and Matheis
OFFICE: RPD
SUBOFFICE: RPD-30
REPORT NUMBER: DOT/FRA/ORD-71/74
SUBJECT: Hazardous Materials
KEYWORDS: hazardous materials; costs; fire exposure; transport; heat transfer; liquefied compressed gases; relief system design; safety; tank cars
ABSTRACT: The report details the findings of a 4-month study contract directed at reducing the hazards of tank car transportation. Principal objectives were to (1) define thermal inputs and associated vapor generation rates for hazardous materials transported in tank cars when subjected to fire exposure. (2) develop performance specifications and conceptual design and application requirements for safety devices preventing catastrophic car failures, and (3) formulate a research program for the design and test verification of recommended safety devices. Prime effort was directed toward the prevention of catastrophic rupture of large-capacity pressure-type cars. A number of shortcomings with existing safety-relief specifications were indicated. A key finding was that the controlling condition in sizing for propane relief should be the liquid feed, or "upset" car condition, and not vapor feed per the current criterion. The net result is a significant undersizing of relief area considering the existing heat flux criterion to be accurate. Analytical studies and review of test data indicate the existing heat flux criterion to be signifi¬cantly low--further increasing the possibilities of overpressure. A staged safety relief system was recommended for cars with liquefied compressed gas ladings. The primary relief element would be a pressure-maintaining system sized for handling abnormal operating conditions other than severe fire exposure. The secondary relief system would be a "dump" type to drop system pressures to levels preventing catastrophic rupture and "rocketing" under severe fire exposure conditions. Both model and full scale test programs are recommended.

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