By Keith Hall
In last month’s column (“Basic Cryogenics,” CryoGas, February 2012, p. 44) I reviewed the National Fire Protection Agency’s (NFPA) “NFPA 59A, Standard for the Production, Storage and Handling of LNG.” Due to the surging interest in liquid natural gas, particularly as a cost effective and environmentally clean vehicular fuel alternative, this month’s follow-on column is a top level review of “NFPA 52, Vehicular Gaseous Fuel Systems Code,” 2010 edition, as far as it pertains to LNG. NFPA 52 also covers gaseous hydrogen GH2, and liquid hydrogen (LH2) fuel systems, which I will discuss next month. Although codes and standards can be very tedious, it is nevertheless important that we have a basic understanding of them.
Below are highlights of some LNG related requirements from NFPA 52 Chapters 11, 12, and 15. This is not an all-inclusive review of the LNG portions of NFPA 52 or an interpretation of that standard. All NFPA standards and codes are available at www.nfpa.org, and it is the equipment owner’s responsibility to ensure that all LNG applications comply with all pertinent regulations and standards. The discussion herein is the author’s opinion only. Experts should be consulted as needed.
LNG Engine Fuel Systems
Chapter 11 of NFPA 52 pertains to the design, installation, inspection, and testing of LNG fuel supply systems for vehicle engines. LNG fuel tanks must be designed, fabricated, and tested per DOT (US Department of Transportation) Specification 4L or the “Rules for the Construction of Unfired Pressure Vessels,” ASME Boiler and Pressure Vessel Code. They must be capable of withstanding a static force in the six principal directions of eight times the weight of the container plus its contents without loss of contents! When filled to the maximum volume with LNG stabilized to the operating pressure, the tank cannot vent (cannot exceed the MAWP) for 72-hours. A newly designed tank has to be drop tested (from 30 feet up) per SAE J2343. Methane detection systems must activate a visual alarm inside the driver’s compartment of an LNG vehicle at a gas concentration of 20–30 percent of the lower flammability limit (LFL), and sound an audible and visual alarm at not greater than 50–60 percent LFL.
LNG Fueling Facilities
According to Chapter 12 of NFPA 52, all LNG dispensing, including mobile refueling, must comply with the requirements of a permanent LNG refueling installation at the point of dispensing fuel. Impounding areas, if provided for LNG transfer, “shall have a minimum volumetric capacity equal to the greatest volume of LNG or flammable liquid that could be discharged into the area during a 10-minute period from any single accidental leakage source or a lesser time period based on demonstrable surveillance and shutdown provisions acceptable to the AHJ (authority having jurisdiction).” When filling the fuel station the LNG must only be transferred at a pressure that will not over pressurize the receiving vessel. When dispensing product the maximum discharge pressure at the fueling nozzle cannot exceed the MAWP of the vehicle fuel tank.
Electrical equipment shall be wired as specified by NFPA 70, National Electrical Code, Class 1, Group D, and Division or Zone as specified in the code. “Exception: Electrical equipment on internal combustion engines installed in accordance with NFPA 37, Standard for the Installation and Use of Stationary Combustion Engines and Gas Turbines.”
LNG Fire Protection
According to Chapter 15 of NFPA 52, fire protection must be based on “sound fire protection and methane detection engineering principles, analysis of local conditions, vehicle operations, hazards within the facility, exposure to or from other property, and the size of the LNG containers.” Guidance factors to assist in making the evaluation are provided in Chapter 15. Planning for emergency response measures is imperative and must be coordinated with local emergency agencies.
Anyone employed in the handling and dispensing of LNG must “be trained in proper handling and operating duties and procedures.” Protective clothing, face shield or goggles, and gloves (ear protection also recommended) shall be provided for all dispensing operators. Operators must “provide and implement a written plan of initial training to instruct all designated operating and supervisory personnel in the characteristics and hazards of LNG used or handled at the site . . . ”
Keith Hall is the Engineering Manager of INOXCVA’s Cryogenic Vessel Alternatives’ LNG/Specialty Products Division in Mont Belvieu, TX, and can be reached at email@example.com.