Topic: Appropriately Sized PRDs for Tank Cars in Class 3 Flammable Liquid Service

NTSB Recommendation: In conjunction with thermal protection systems called for in safety recommendation R-15-29 [[14??]], require that all new and existing tank cars used to transport all Class 3 flammable liquids be equipped with appropriately sized pressure relief devices that allow the release of pressure under fire conditions to ensure thermal performance that meets or exceeds the requirements of Title 49 Code of Federal Regulations 179.18(a), and that minimizes the likelihood of energetic thermal ruptures.

PHMSA Action: PHMSA published a final rule on May 8, 2015 entitled "Hazardous Materials: Enhanced Tank Car Standards and Operational Controls for High-Hazard Flammable Trains" (HM-251; 80 FR 26643) requires thermal protections systems for tanks cars used in high hazard flammable trains (HHFTs). These thermal protection systems must include a reclosing pressure relief device that conforms to § 173.31. The combination of thermal protection systems with an appropriately sized relief device increases tank car protection in a pool fire environment such that it can delay, or even prevent, thermal ruptures caused by extreme heat, increasing internal tank pressure, and tank wall thinning.

Latest PHMSA Response: Letter sent to the NTSB on May 4, 2015.

NTSB Status: OAA