Understanding Tolerable Risk Criteria – Considering the Growth of LNG Transportation

Cheap natural gas and the aim to lower emissions from combustion systems such as stationary power generation and heavy haul vehicle engines has led to a multi-industry effort to convert to natural gas equipment. Natural gas pipelines can reach most of the U.S., but there are many areas where shipping liquefied natural gas (LNG) via truck or train may be the most economical solution. This article focuses on shipping LNG via rail and benchmarking the risk this poses. Although similar to other hazardous materials, LNG shipping via rail is a new endeavor in the U.S., and the regulations don’t currently allow this to happen. The Federal Rail Administration (FRA) is the government entity that regulates rail shipping, and after a series of crude oil train accidents over the last decade has implemented a requirement for a risk-based analysis in order to get approval to ship high hazard flammable trains (HHFT). Further, the FRA has issued specific guidance related to risk assessment for LNG trains. Quantitative Risk Assessment (QRA) is one tool that can be applied to evaluate the risks posed by shipping LNG. This falls into a special class of QRA called Transportation Risk Analysis.

But how do we evaluate the quantified risk for shipping LNG? How can demonstrate that the risk of shipping LNG is acceptable to our society? Currently, the U.S. federal government has not explicitly provided risk criteria for evaluating acceptability of shipping LNG via specific routes. In contrast, international regulators and industry organizations have implemented tolerable risk criteria for determining acceptability of new technologies, but their underlying bases may not be apparent. In this paper, we will demonstrate how existing stationary LNG plant tolerable risk criteria can be used to develop criteria for LNG transportation risk. The inappropriateness of directly applying these existing stationary plant risk criteria to transportation will be explained, and other existing HHFT commodities (propane (LPG) for example) will be used to benchmark against the stationary LNG plant criteria and to show how these criteria can be modified to apply to transportation risk. Ultimately, the risks will be quantified for LNG HHFTs and compared to existing HHFTs to show that the newer fuel, LNG, poses reasonable and equivalent risks to many of the other HHFTs currently shipped through the U.S. From this work, a tolerable risk criterion for LNG shipping via rail will be proposed.