Effects of Lading Conditions on Puncture Resistance and Release Probability of HAZMAT Tank Cars
Authors: Kirkpatrick Steven W. 
Published: June 2024

The derailment on February 3, 2023, in East Palestine, Ohio resulted in both a significant release of hazardous materials (HAZMAT) and fires. As a result of the derailment, and subsequent NTSB and FRA investigations, there will likely be a renewed interest in the safety of transporting HAZMAT in DOT-111 general-purpose tank cars. However, the past regulatory efforts related to the transport of high-hazard flammable commodities in DOT-111 tank cars was focused on the tank car design. There was limited consideration of alternative loading and operational conditions that could have an equally significant impact on the safety and probability of release for these tank cars.

The past regulatory responses to safety concerns for HAZMAT transport in railroad tank car safety have developed requirements for strengthening of the tank shell. The March 2009 regulations on poison inhalation hazard (PIH) tank cars (Federal Register, 74 FR 1769) required commodities to be shipped in tank cars with higher pressure ratings (thicker tank walls). Similarly, the July 2015 regulations on high-hazard flammable tank cars (Federal Register, 80 FR 26643) requires the use of DOT-117 tank cars for these commodities instead of the DOT-111 tank cars previously used. The DOT-117 has both a thicker tank shell and requires an external protective jacket compared to the DOT-111 tank. These simple upgrades in the tank thickness/strength, are easy requirements to specify. The upgrades to the tank structure are also relatively simple to evaluate, either in terms of the expected reduction in the conditional probability of release (CPR), or for improved puncture resistance in an impact test or analysis.

The effects of different tank car commodities and loading conditions have been evaluated in past tank car safety studies. The effects of the loading conditions, such as the internal pressure and the magnitude of the outage volume (vapor space above the lading), can produce significant changes in the puncture resistance. However, these effects have not been sufficiently considered as a factor for improving safety of HAZMAT transport by rail.

The objective of this study is to evaluate the potential for reductions in HAZMAT releases from modifications to the tank loading conditions. Validated tank car impact and puncture analysis methodologies are used to evaluate the effect of these modifications (e.g., larger outage volumes). For example, we analyze the loading conditions required for a DOT-111 tank car to have an equivalent tank shell puncture resistance as a DOT-117 tank car loaded with crude oil at nominal operating conditions. These relative comparisons could be applied by decision makers to make informed choices on the best approaches for improved railroad HAZMAT safety.

The results of the study show that the CPR for a DOT-111A100W1 can be significantly reduced, when loaded with larger outage volumes than required to meet the 1% minimum outage requirement. Applying these findings show that there are simple methods that can be applied to improve the safety of HAZMAT transport by rail. For example, shipping HAZMAT commodities in tank cars that are larger in volume than required based on the minimum 1% outage requirement and gross rail load (GRL) limit, will reduce releases and increase safety.