LNG takes up 1/600th of the volume of the gaseous state of natural gas, but retains all of the energy potential. Thus, the energy potential of a specific volume of LNG is significantly greater than the same volume of natural gas in its gaseous state. The safety of LNG facilities is addressed through the inherent characteristics of LNG and through the design and operation of LNG facilities and transportation modes.
In land-based LNG facilities, impoundment structures around LNG tanks and pipelines are designed to control the spread of LNG if a release occurs. Fire and vapor suppression systems are installed to mitigate the consequences of a release. Gas detectors, fire detectors, and temperature sensors automatically activate firefighting and vapor suppression systems. In the event of a fire, water spray may be used for heat affected exposures, or high expansion foam may be used to reduce radiant heat impact on exposures. At some facilities vapor fences are installed to prevent vapors from extending onto adjacent properties. Vacuum jacketed pipe also provides an additional layer of protection in the event of a release of the inner pipe. Emergency shutdown devices activate when operational parameters extend beyond the normal range. The LNG facility operator must develop and follow detailed maintenance procedures to ensure the integrity of various safety systems.
Prior to commencing operations, the LNG facility operator must establish detailed procedures that specify the normal operating parameters for all equipment. When a piece of equipment is modified or replaced, all procedures must be reviewed and modified if necessary to assure the integrity of the system. All personnel must complete training in operations & maintenance, security, and firefighting. The operator must coordinate with local officials and apprise them of the types of fire control equipment available within the facility. Additionally, Federal regulations require tight security for the facility, including controlled access, communications systems, enclosure monitoring, and patrols.
LNG SAFETY RESEARCH AND STUDIES
PHMSA funds LNG research through PHMSA's Pipeline Safety Research and Development grants. LNG projects include:
- DTRS56-04-T-0005, Modeling and Assessing a Spectrum of Accidental Fires and Risks in a LNG Facility
- DTPH5615T00005, Comparison of Exclusion Zone Calculations and Vapor Dispersion Modeling Tools
- DTPH5615T00008, Statistical Review and Gap Analysis of LNG Failure Rate Table
To view all of PHMSA’s R&D projects go to http://primis.phmsa.dot.gov/matrix/.
Historical Review of Vapor Cloud Explosions (VCE)
Due to the recent abundance of domestic shale gas, LNG export terminals are now being constructed that liquefy vast volumes of natural gas. These facilities require significantly greater quantities of refrigerants to liquefy the natural gas than the amount typically used at a peak shavers or small scale facilities. Most refrigerants gases and blends used at the export facilities contain ethane, propane, ethylene, and iso-butane and are referred to as heavy hydrocarbons. These gases are similar to gases that have resulted in VCEs at petrochemical facilities. However, PHMSA is not aware of any reliable reports of explosions of outdoor vapor clouds of natural gas and does not believe that there is a risk of vapor cloud explosions (VCEs) due to a release of methane in an open area.
PHMSA sponsored the Review of Vapour Cloud Explosion Incidents report with the primary objective to improve the scientific understanding of vapor cloud development and explosion in order to more reliably assess hazards at large Liquid Natural Gas (LNG) export facilities. It is important to note that today’s LNG export facilities have many layers of protection that were not in place at the facilities in the report. Many lessons learned from these events have resulted in safety measures that are required in LNG facilities today. The aim of reviewing the particular incidents in this report is the extensive forensic evidence available that provides the information needed to study how the vapor cloud formed and ignited, the amount of overpressure exerted, and other information about the mechanism of VCE.
Multiple studies have been performed over time regarding the safety and risks of LNG. Many of these focused on the safety of LNG tankers (ocean going ships) since they transport large volumes of LNG and enter ocean ports that may be in close proximity to populated areas. One example of such a study is found in the U.S. Department of Energy (DOE) Report to Congress in 2012 on Liquefied Natural Gas Safety Research. Others, such as the Liquefied Natural Gas (LNG) Import Terminals: Siting, Safety, and Regulation study from the Congressional Research Service, focus attention on the safety of LNG terminals and infrastructure. These and other reports address the physical hazards of LNG, such as pool fires, flammable vapor clouds, fire, and cryogenic impacts. Some reports also address ship safety, terminal safety, liquefaction facility safety, and security.