Development of LNG Facilities Safety Standards

Pursuant to the Liquefied Natural Gas Terminal Act of 1977, the California Public Utilities Commission has adopted a comprehensive set of safety regulations entitled “Liquefied Natural Gas Facilities Safety Standards” as Part III of General Order No. 112-D (Public Utilities Commission of the State of California, 1979). The standards prescribe rules governing the design, construction, and the safety aspects of the operation and maintenance of LNG facilities in California. These LNG safety regulations are the most comprehensive in the United States today. The intent of the safety standards is to satisfy the requirements and to meet the objectives mandated by the Public Utilities Code to promote and safeguard the public health, safety and welfare. The goal in establishing the safety standards is to provide a high level of safety at LNG facilities by giving consideration both to the special requirements imposed by the low temperature of LNG and to the methods of controlling the potential causes and consequences of an accidental release of LNG in either a liquid or gas form. In order to reduce the probability of occurrence of failure within LNG facilities and to reduce the anticipated consequences of such a failure to a level that will safeguard the health and safety of the public, the Commission has adopted a four-level approach to the solution of safety problems (Ong, 1978). The “first level” involves the selection of conservative design criteria by using the probabilistic or deterministic method. The design criteria will provide a uniform level for all natural and manmade hazards that might affect the facilities. The level of design selected will assure that no hazardous external events (such as earthquake, wind, flood, or aircraft impact) would have a significant probability of leading to an unsafe condition. Critical components such as LNG storage tanks, their impoundment systems, and hazard protection systems will be designed so that each factor which might result in a catastrophic failure has a 99.5 percent probability of not being exceeded in 50 years. This represents a design event which has a recurrence interval of 10,000 years. In addition, components of an LNG facility will be classified into three categories in relation to the reliability characteristics and potential safety hazards associated with each component. The classification procedure will simplify design by designating different levels of safety performance for each category of components and thus enhance plant reliability and the protection of capital investment. At the “second level,” added reliability will be gained by requiring (a) redundancy of hazard sensors in critical locations, and (b) valving and other installations designed to control safely the flow or monitor the containment of LNG and natural gas throughout the plant. At the “third level,” assuming a failure of containment of the LNG for any reason, impoundment systems would be designed to contain the spilled LNG. The standards also provide a 2.5 percent vapor concentration criterion at the property line to prevent the release of combustible gas beyond the plant boundary. Lastly, if LNG should spill and ignite in spite of all precautions, fire protection equipment would be activated to mitigate or extinguish the hazard. Thermal exclusion distance requirements call for the plant boundary to be located at sufficient distance from the storage and impoundment area so that unreasonable heat flux levels could not reach persons exposed to the fire beyond the boundary. The standards provide the criterion of 1,600 Btu/ ft2-hr as the allowable heat flux level at the plant boundary.