Saturday, December 14, 2019

LNG by Rail NPRM Comments – 12-14-19

With just a little over two weeks left before the end of the comment period on the DOT’s Pipeline and Hazardous Material Administration (PHMSA) notice of proposed rulemaking (NPRM) that would allow the rail transportation of liquified natural gas (LNG), there have only been 76 comments posted to the Docket. The vast majority of those comments have been from individual who are generally opposed to the NPRM, but the opposition does not seem to be an organized letter writing campaign.

Five of the comments submitted to date do not fall into the private citizen comment category (note: all links are .PDF download links):

Port of Brownsville, Texas (in opposition to a local LNG facility, not about LNG by rail);

The fifth comment was my comment that I posted here back in October.

Not Enough Safety Data

Three of the commenters (ignoring the Brownsville comments) above made frequent mention that PHMSA and the Federal Railroad Administration (FRA) have not completed a variety of safety tests currently planned and/or underway related to the shipment of LNG by rail. These tests include:

• Puncture resistance testing for DOT 113C120W railcars;
• Pool fire testing for DOT 113C120W railcars;
• FRA testing of an alternative ‘LNG tender’ design; and
• FRA testing of an alternative ISO tank design;

Additionally, the NTSB notes that the limited data on crashes involving DOT 113 railcars in other cryogenic service does not provide a large enough statistical universe to offer an reliable predictive data about the potential safety of LNG shipments, especially if the size of the fleet increases as projected.

The VOB comment expresses concerns about the adequacy of emergency response information that is available for a large-scale release from a multi-unit LNG train.

NOTE: The PHMSA LNG by rail special permit did include a training special condition for the shipper to provide emergency response training to all emergency response agencies that could be affected between the authorized origin and destination.

Operational Controls

The NTSB comments include a lengthy discussion about the operational controls that should be part of the LNG by rail rulemaking. They recommend:

• Rail route security assessments in accordance with 49 CFR 172.820;
• Speed restrictions – 40 mph in high-threat urban areas, 50 mph elsewhere;
• Enhanced breaking requirements – ECP, 2-way end-of-train devices, or distributed power systems;
• LNG railcar placement – more than 5 cars away from locomotive or occupied equipment to protect train personnel in event of derailment.

NOTE: The special permit did include an enhanced breaking equipment special condition.


It is interesting that there have been no comments submitted to date from any of the environmental or transportation safety advocacy groups that we have seen with earlier NPRMs for crude oil shipments for instance. I am particularly surprised that there have not been any letter writing campaigns organized by these organizations. Such campaigns have little effect on regulatory agencies (particularly in a Republican Administration), but they do have a positive effect on monetary contributions to those organizations.

One issue that none of the commenters to date (myself included) have raised is the peculiar vulnerability associated with double-shell railcars used in the shipment of cryogenic liquids. The annular space between the two shells has the air evacuated to very-low pressure (vacuum) levels. This is used to help prevent environmental heat from raising the temperature (and the resulting pressure) in the internal tank in much the same way that a vacuum thermos bottle keeps one’s coffee hot.

PHMSA has touted this double shell design as an additional way of preventing leaks of the LNG during an accident; a puncturing object would have to pass through the outer shell, the annular space and the inner shell for a leak to occur. Except….. During an accident where the outer shell is punctured, environmental air enters the annular space and heat-transfer immediately begins. In the event of a pool fire in the vicinity (not even necessarily with ‘flame impingement’ on the car), the heat transfer is much higher than normal.

In a relatively short amount of time (depending on environmental conditions) the interior tank pressure is going to raise above the pressure set for the pressure relief valve and the tank car will begin to vent. If the PRV were equipped with an ignition device, an impressive flame would accompany the screaming sound of quickly escaping natural gas. Without a flaring device on the PRV, a gas cloud would form that would continue to expand until it reached some other ignition source. In a best-case scenario the cloud would burn back to the PRV which would then become an unintended flare device. Oh yes, and the local air temperature would increase significantly and the heat transfer rate would increase.

If the heat transfer rate were high-enough the pressure would continue to rise even with the PRV venting. At some point the pressure in the tank could rise to the point where the rupture disk would release large volumes of natural gas into the environment. Because of the larger opening of the rupture disk, the burn-back of the vapor cloud could potentially result in the flame burning back into the confined space of the rail car where detonation would likely result.

This is one of the reasons that PHMSA’s special condition of requiring remote pressure monitoring of each railcar is so important; important, however, only if the information on rising pressure levels can be provided to emergency responders in a timely manner. Fires in and around LNG railcars should aggressively fought to help keep the LNG cars in a safe temperature/pressure situation, but only until pressures start to approach the PRV release pressure. Then fast evacuations of firefighting personnel are the main priority.

Determining how high the pressure can reach before safe evacuations should be ordered is one of the reasons that DOT needs to test these railcars to failure in fire situations in both puncture-free and loss-of-vacuum situations. And why the pressure monitoring needs to be conducted on both the annular space and the inner tank.

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