PHMSA Response Letter
Ms. Lisa M. Tonery
Fulbright & Jaworski L.L.P.
666 Fifth Avenue, 31 st Floor
New York, NY 10103-3198
Dear Ms. Tonery:
As counsel for Downeast LNG, Inc. (Downeast or the Company), you have asked for a written interpretation on two questions related to your client's proposal to build a liquefied natural gas (LNG) import terminal in the town of Robbinston, Maine (Robbinston LNG Import Terminal or the Terminal). Specifically, you have asked whether Downeast may use its alternative source term model (DLNG Source Term Model) to comply with the vapor-gas exclusion zone requirements in 49 C.F .R. § 193.2059 . You have also asked whether the Company must examine the effects of jetting and flashing to comply with those same requirements.
Under the conditions described in this letter, Downeast may use the DLNG Source Term Model to calculate the vapor-gas exclusion zone for the sumps at the Robbinston LNG Import Terminal. The Company must also examine the effects of jetting and flashing in siting appropriate facilities at the Terminal, including pressurized piping or equipment, to comply with our vapor-gas dispersion exclusion zone requirements.
The Pipeline and Hazardous Materials Safety Administration (PHMSA) issues federal safety standards for siting LNG facilities.! Those regulations require that an operator or governmental authority control the activities that occur within a specified distance around the facilities at an LNG plant, to protect the public from unsafe levels of thermal radiation and flammable vaporgas dispersion in the event of an accident. Certain mathematical models and other parameters must be used to calculate the dimensions of these "exclusion zones."
In the case of vapor-gas dispersion, two different computational models are already authorized for use by regulation: (1) the DEGADIS Dense Gas Dispersion Model (DEGADIS), a model developed by the U.S. Coast Guard and Gas Research Institute (GR!) to simulate the downwind dispersion of dense gases in the atmosphere, and (2) FEM3A, another dispersion model designed "to account for additional cloud dilution which may be caused by the complex flow patterns induced by tank and dike structure."
Downeast intends to calculate the vapor-gas dispersion exclusion zone for the Robbinston LNG Import Terminal with DEGADIS, an integral model that requires the user to input a "source term." The source term is designed to simulate the physical phenomena that occur immediately after an LNG release, but prior to atmospheric dispersion.
You have asked whether the Company may use a new source term model, the DLNG Source Term Model, to perform the exclusion zone analysis for the sumps at the Terminal. You state that this new model uses conservative assumptions for the effects of pool spreading, vapor production, and vapor retention. In your opinion, that makes it suitable for use with DEGADIS under our regulations.
The source term used as the input for DEGADIS must have a suitable basis to comply with our Siting Requirements. "Otherwise, a user could select whatever source term is likely to produce the most favorable outcome, e.g., the smallest or largest possible exclusion zone, or even at random." Such a result would not be consistent with the limitations of DEGADIS or our statutory obligation to protect the public from the hazards associated with an LNG plant. For these reasons, the utmost care must also be exercised in evaluating the suitability of any such model, a task that involves "making predictions, within [PHMSA' s] area of special expertise."
We further note that the proponent of an alternative source term model previously had to petition for, and receive, the Administrator's approval to use that model to comply with our vapor-gas dispersion exclusion zone requirements. However, our predecessor agency repealed that requirement in a March 2000 final rule. Consequently, the Administrator's approval is no longer an absolute prere~uisite to using an alternative source term model with DEGADIS under our Siting Requirements.
In our opinion, the DLNG Source Term Model can be used with DEGADIS to calculate the vapor-gas dispersion exclusion zones for the sumps at the Robbinston LNG Import Terminal. Downeast has demonstrated, through the use of a parametric analysis, that an instantaneous pool spreading scenario across these particular sump floors will produce the longest flammable vaporgas cloud. The Company has also shown that its heat transfer methodology is appropriate. As confirmed in the documents submitted with your letter, that methodology "assum[ es] perfect thermal contact between [the] pool and [the] ground, and only vertical temperature gradients in the ground," and the conduction is modeled "by the one-dimensional Fourier conduction equation in the ground, with an initial state where the ground is uniformly at ambient temperature, and assumes the boiling temperature of LNG as soon as the spreading pool reaches" the sump floor. Finally, the model conservatively assumes that none of the produced vapors is retained by the sump walls.
These conservative assumptions provide the model with a suitable basis for use in this particular application. Accordingly, we conclude that the DLNG Source Term Model can be used with DEGADIS to calculate the vapor-gas dispersion exclusion zones for the sumps at the Robbinston LN G Import Terminal.
The phenomena known as jetting and flashing can occur if pressurized piping or equipment fails. Jetting can cause released LNG to propel beyond an impoundment system, or result in fragmentation and formation of aerosols. It can also erode earthen dikes, expose equipment to cryogenic liquids, or project LNG or its vapors onto adjacent properties. Flashing is the instantaneous vaporization of released LNG due to exposure ambient pressure and temperature. Like jetting, it can cause fragmentation and formation of aerosols and project vapors onto adjacent properties. Understanding the effect of these phenomena is important to public safety, as they can create hazards (e.g., cascading failures, the loss of containment, and the instantaneous formation of a vapor-gas cloud) that are capable of affecting offsite properties and activities.
You state that Downeast has not considered jetting and flashing in siting the Robbinston LNG Import Terminal, because the "Part 193 Subpart B LNG Requirements do not speak to either flashing or jetting and flammable vapor production rate in the event of an LNG leak." You have asked PHMSA for an opinion to that effect, namely, that "[j]etting and flashing are not to be considered with respect to the exclusion zone analysis of 49 CFR Section 193.2059." Contrary to your position, we conclude that these phenomena should be considered in appropriate cases.
The source tenn model used as the input for DEGADIS must have a suitable basis to comply with our vapor-gas exclusion zone requirements. In the case of jetting and flashing, there is no dispute that a failure of pressurized piping or equipment may cause LNG to vaporize in the air. Using a source tenn model that ignores that effect (or any other phenomena that has a similar influence on the discharge, vaporization, or conveyance of LNG) could distort the downwind dispersion of vapor gas and compromise the integrity of an operator's exclusion zone analysis. Such a result would not ensure that the siting of an LNG facility occurs in a manner consistent with our statutory obligations. Consequently, a source tenn model should account for the effects of jetting and flashing in appropriate cases, including where a design-spill scenario involves a failure of pressurized piping or equipment.
Consideration of jetting and flashing might also be required outside the confines of an exclusion zone analysis. For example, steps must be taken to ensure that any released LNG is retained within the limits of plant property. That includes "grad[ing], drain[ing], or provid[ing]" certain areas "with [an] impoundment" to reduce "the possibility of accidental spills and leaks that could endanger im;ortant structures, equipment, or adjoining property or that could reach waterways." I Similarly, site-specific factors that have a bearing on the safety of plant personnel or the surrounding public must be evaluated in siting an LNG facility, and appropriate responsive safety measures must be incorporated into the design or operation of that facility. However, as you did not request an interpretation of these or any other provisions, we simply note in closing that an operator must demonstrate that a new LNG facility complies with our Siting Requirements.
Downeast may use the DLNG Source Tenn Model to calculate the vapor-gas exclusion zone for the sumps at the Robbinston LNG Import Tenninal. The Company must also examine the effects of jetting and flashing in calculating the vapor-gas dispersion exclusion zone for any appropriate LNG facilities, including pressurized piping or equipment, to comply with the Siting Requirements in Subpart B of 49 C.F.R. Part 193.
Jeffrey D. Wiese
for Pipeline Safety