Improving Prevention and Mitigation Efforts Related to Accidental Releases of LNG

PresentationLiquefied Natural Gas (LNG) is a rapidly growing industry, both in terms of the increase in export terminals, as well as the growing number of regasification plants required to put natural gas back into pipelines. In the selection of a location or design of new facilities, the potential impact of an accidental release must be evaluated. Some of the protective and mitigative measures required by onshore storage and handling facilities for reducing impacts due to accidental releases are dictated by 49 CFR 193, with design requirements based on accidental leakage calculations following NFPA 59A. In the United States, these measures are reviewed by the US Pipeline and Hazardous Materials Safety Administration (PHMSA). Siting and construction of onshore and nearshore LNG facilities are authorized by the Federal Energy Regulatory Commission (FERC). While various specific regulations and codes require some measures, a detailed evaluation of the potential consequences may indicate that additional mitigative actions are needed. PHMSA requires both pool fire and dispersion models from scenarios of accidental releases of accumulated LNG in containment basins as per the 49 CFR 193 regulation in order to meet the NFPA 59A standards. Containment basins include LNG tank impoundments, trenches, and sumps, which are often modeled with LNG accumulating due to a guillotine break of the largest pipe. While accidental releases of LNG can be mitigated by trenches, sumps, and other forms of impoundment, the effectiveness of the mitigation is impacted by the nature of the trenches and containment basins. Any positive or negative impact is difficult to predict without complex evaluation. For example, if the tank itself is designed in such a way that a rip or rupture of the inner tank wall followed by thermal cracking of the external wall is a credible scenario, the elevation of a resulting hole as well as the size of it could render the basin walls inadequate depending on the location and extent of tank damage and impoundment geometry. Also, in terms of trenching used to direct LNG to containment basins, the geometry of the trench itself combined with the wind direction can have a significant impact on the generated plume size with LNG accumulation. In particular, a long linear span of trenching that is parallel with the wind direction may result in enough accumulation to generate a large plume well in excess of 1 kilometer. CFD models predict that the magnitude and location of an LNG release, the weather conditions, the regional terrain, release impingement, and the duration of the release can all greatly influence how far a combustible gas cloud will travel. Proximity of pipelines to vehicular or railway traffic can lead to an increased frequency of pipe breaks, and sometimes older facilities may be lacking in protective measures such as vapor fences that could better protect the public. Potential causes of releases will be explored and a range of possible improvements with prevention and mitigation measures will be discussed