Reducing hazardous materials releases from railroad tank car safety vents

The leading cause of hazardous materials releases in railroad transportation over the 5 years prior to this research was burst frangible disks on tank cars. These burst disks occur as a result of pressure surges in the tank car safety vent during transportation. More than a dozen different surge pressure reduction devices (SPRDs) have been developed to protect the frangible disk from these surges. A statistical analysis of tank cars in service indicated that cars equipped with SPRDs experienced a lower rate of leakage due to burst frangible disks than similar cars without SPRDs. This analysis, however, did not provide sufficient resolution to determine the relative effectiveness of the different SPRD designs. A series of controlled experiments was conducted to determine the surge reduction effectiveness and the flow performance of different SPRDs. These tests showed that there were significant differences in the performance of the various surge pressure reduction devices in both surge reduction and flow rate. The results of these tests will help tank car builders, owners, and operators improve the safety performance of tank cars by installing SPRDs that will reduce non-accident-caused releases of hazardous materials and still function adequately to relieve pressure when necessary. The results also will provide a basis for setting SPRD performance and testing requirements and identify promising design elements for new SPRDs.