MYTH 1: LNG IS DANGEROUS! (NOT!)
The notion that LNG represents a waiting explosion never fails to surface. During the years of controlled testing by independent laboratories and hundreds of thousands of gallons of (intentionally) spilled LNG, ignition of a vapour cloud has not yet caused an explosion. In fact, some testing involved initiating the combustion of the gas cloud with high explosives. The strength of the detonation was no stronger than that delivered by the explosives. Conclusion: The ignition of LNG or LNG vapour will not cause an explosion in an unconfined environment.
Natural Gas is only combustible at a concentration of 5 to 15% when mixed with air. Furthermore, its flame speed is very slow. These facts may best be experienced by a simple demonstration often done at LNG fire schools. A large pit (e.g., 20' x 20') is filled with LNG, allowing the vapour cloud to drift with the wind. The cloud is ignited with a torch from the downwind side. Ignition typically occurs near the visible fringes of the cloud. The resulting flame front moves back toward the pit at a speed only slightly faster than a walk. The pronounced lack of detonation or over-pressure leaves a lasting impression on anyone who has witnessed the ignition of a similar size pool of gasoline or propane.
MYTH 2: LNG VAPOUR CLOUDS ARE HUGE AND DEADLY! (NOT!)
Traditionally, LNG vapour dispersion studies have focused on the "worst case", catastrophic failure of enormous storage tanks (25,000,000 gallons) or guillotine failures of ship unloading lines (50,000 gpm for ten minutes). Potential vapour clouds from vehicular LNG are, on the other hand, dwarfed by these "design spills".
The size and travel of an LNG vapour cloud is a function, most of all, of the size and rate of the spill. To a lesser degree, the size and surface of the affected area, atmospheric conditions and LNG pressure also plays a role. Small spills will quickly vaporise on contact with the ground. LNG vapour becomes buoyant in air at as the gas/air mixture rises to temperatures above -160°F. Therefore, it will dissipate rapidly into the atmosphere. Spills large enough to form a dense vapour cloud will similarly dissipate due to the heat from the ground over which the cloud migrates.
Wind plays an important role as well. Conditions of little or no wind reduce movement of the cloud away from the source. The turbulence of higher winds causes rapid dispersion due to the mixing of the vapours with the ambient air.
MYTH 3: LNG IS DIFFICULT (OR COSTLY) TO KEEP COLD! (NOT!)
Stored LNG is analogous to boiling water, only 470° colder. The temperature of boiling water (212°F) does not change, even with increased heat, as it is cooled by evaporation (steam generation). In much the same way, LNG will stay at near constant temperature if kept at constant pressure. This is a phenomenon called "auto refrigeration". As long as the steam (LNG vapour boil off) is allowed to leave the tank, the temperature will remain constant.
If the vapour is not drawn off, then the pressure and temperature inside the vessel will rise. However, even at 100 psig, the LNG temperature will still be only about -200°F. It is this pressure rise that may require venting of the on-board fuel tanks after idle periods of 7 to 14 days.
MYTH 4: LNG TECHNOLOGY IS NEW! (NOT!)
The liquefaction of natural gas dates back to early in this century. LNG has been used as vehicle fuel since the mid-60s. Let's go beyond the specific to a more generic look at the technology. LNG is a cryogenic (very low temperature) liquid.
Cryogenic liquids are a common part of life today and, as such, have been around for some time. The technology of storage and handling of all cryogenic liquids is very similar, independent of the product. Check behind any hospital and you will most likely find a vertical white tank containing liquid oxygen (-296°F). Electronics firms, food processors, and many other operations routinely store and use liquid nitrogen (-320°F).
Liquid hydrogen (-423°F), along with liquid oxygen, is used as rocket engine fuel. The low temperatures of liquid helium (-452°F) are critical in the operation of MRI medical diagnosis equipment. Trucks carrying any of these liquids, along with LNG, are common sights on the highway.