Thursday, October 24, 2019

PHMSA Publishes LNG by Rail NPRM

Today the DOT’s Pipeline and Hazardous Material Safety Administration (PHMSA) published a notice of proposed rulemaking (NPRM) “Hazardous Materials: Liquefied Natural Gas by Rail” in the Federal Register (84 FR 56964-56977). The rule would make changes to the Hazardous Materials Regulations to allow for the bulk transport of Methane, refrigerated liquid, commonly known as liquefied natural gas (LNG), in DOT-113C120W specification rail tank cars. The rulemaking was initiated in response to a petition for rulemaking [.PDF download link] from the Association for American Railroads (AAR).

Tank Car Specification

The AAR petition requested that PHMSA consider authorizing the use of current DOT-113C120W and a new DOT-113C140W specification tank car for the transport of LNG by rail. In this rulemaking PHMSA is only proposing to authorize the use of the DOT-113C120W specification tank car which are currently in service for the transportation of other flammable cryogenic liquids. PHMSA notes that they “anticipate that DOT-113 specification tank cars will need to be manufactured to satisfy the demand for transporting LNG as the current fleet of these tank cars is used for the transportation of ethylene and other cryogenic liquids.”

The rulemaking would amend 49 CFR 179.319(d)(2) to add the following pressure relief requirements for LNG:

Maximum pressure when offered for transportation – 15 psig;
Design service temperature – minus 216˚F; and
Maximum start to discharge pressure – 75 psig

Operational Controls

The NPRM is not proposing to impose any additional operational controls beyond those currently required for flammable cryogenic liquids. It is, however, seeking comments on whether or not the following controls should be considered in the final rule:

Incorporate by reference AAR Circular OT-55 key train and/or key route provisions;

LNG Characteristics

There is a lengthy discussion in the preamble about the characteristics of LNG; particularly the characteristics of LNG fires. The discussion of a vapor cloud fire is important:

“If an LNG vapor cloud is ignited before the cloud has been dispersed or diluted to below its lower flammability limit, a flash fire will occur. Unlike other flammable liquids and gases, a LNG vapor cloud will not ignite entirely at once. If ignited, the flash fire that forms has a temperature of about 1,330 °C (2,426 °F). The resulting ignition leads to a relatively slow (subsonic) burning vapor fire which travels back to the release point producing either a pool fire or a jet fire [emphasis added]. The radiant heat effects from such a flash fire does not extend to distances significantly larger than the width of the flammable cloud. The slow burning vapor fire will not generate damaging overpressures (i.e., explosions), if unconfined. To produce an overpressure event, the LNG vapors need to be within the flammability range and ignited, and either be confined within a structure or the travelling flame in the open encounters structural obstructions (e.g., houses, trees, bushes, pipe racks, etc.) that can increase the flame turbulence significantly when the flash fire reaches the source of vapor (boiling LNG), if there is still a liquid pool of LNG evaporating at that time, a pool fire will result.”

DOT 113 Accident History

The preamble includes a discussion of the accident history of the DOT 113 tank car. It describes only one incident in 37 years in which a fire occurred as a result of a derailment involving flammable cryogenic liquids transported in DOT 113C120 tank cars. According to a local news report the fire was relatively unremarkable.

Public Comments

PHMSA is soliciting public comments on this NPRM. Comments may be submitted via the Federal eRulemaking Portal (; Docket # PHMSA-2018-0025). Comments need to be submitted by December 23rd, 2019.


If the public comments on PHMSA’s LNG by rail special permit are any indication (2,973 comments to date) there will be a large public outcry against this NPRM. It will come mainly from people who have not read the NPRM and particularly did not read the discussion on LNG characteristics and the accident history of the DOT 113 railcar.

We are seeing an increasing amount of natural gas being produced in oil fields in the United States. It makes no economic sense nor environmental sense to not use that methane as either a fuel or a chemical feedstock. Either of those uses will require transporting the natural gas from where it is produced to where it is used or to where it is shipped to our trading partners via ocean going vessels. The pipeline infrastructure (the safest way to ship either natural gas or LNG) is not in place to provide that transportation. Currently the only other authorized way to ship the material is by truck. That mode has more safety issues than does rail, and the dwindling supply of hazmat qualified truck drivers provides an additional impediment to transporting large quantities of LNG by truck.

Economically and environmentally this rulemaking is necessary. There are some changes that I think need to be made and I will address those in a separate blog post with subsequent submission as a comment on this NPRM.

I urge everyone with an interest in this topic (pro and con) to closely read this NPMR, consider what PHMSA is proposing (and missing) and submit well-reasoned comments to help to improve this rulemaking.

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