How Dangerous is LNG? part 2

My purpose in posting this article is to educate any readers about LNG based upon my knowledge and 30 years' experience. I am not aware of anyone who claims that LNG isn't dangerous. It's a cryogenic liquid whose vapor form is flammable natural gas. But its physical nature keeps it from being the doomsday material that its opponents make it out to be. In fact, it is far less dangerous than many other bulk fuels, especially propane, the major ingredient in your backyard grill.

            LNG is produced at places having huge natural gas supplies, but little local use for it. Algeria, Qatar, Libya, Malaysia and Indonesia are major exporters of LNG. The US has one export facility, in Kenai, Alaska, that sends a relatively small amount to Japan.

            Production plants store LNG in large insulated tanks before loading it onto special-built tanker ships fitted with insulated cargo tanks. Because the LNG is so cold, it is kept liquid at almost atmospheric pressure, less than three pounds per square inch (PSI). By contrast, propane (LPG) must be kept at close to 200 PSI to remain liquid. This is an extremely important point, as we shall see.

            LNG tankers come in two basic cargo tank designs. In the older design, spherical tanks sit on a cylindrical skirt with much of the tank rising above the ship's main deck. A three foot thick layer of insulation covers the tanks, and a distinctive spherical steel jacket seals the insulation from moisture and physical damage.

           "Membrane" type tanks are built into the contours of the ship's hull, giving these tankers a much lower profile. There are several variations of the membrane style, but all are made of high alloy metals surrounded by a layer of insulation and protective steel jacket. 

            Both types of tanker have double hulls. The space between the two hulls holds ballast water when the tanks are empty, which helps keep the ships stable.

            At the receiving terminal, tankers pump the LNG into storage tanks on shore, where it awaits vaporization for sending out by pipeline. Only in the vaporization stage, when the LNG becomes natural gas, is the pressure raised above near atmospheric. Terminals typically use a hot water bath, though other types of vaporizers are used. There are currently four receiving terminals in the US: Everett, MA; Cove Point, MD; Elba Island, GA and Lake Charles, LA. Another is under construction at Freeport, TX. A California energy company is building another in Baja California, just across the border from San Diego.

           Threats to an LNG receiving terminal are the same as those for a refinery or petrochemical plant: (hurricane, earthquake, tsunami and terrorist attack). Environmental threats have been considered in plant design for many decades and have never caused a significant failure in a plant.

In comparing relative danger, we must look at what happens in case a threat comes to pass. The threat of a widely spreading LNG spill is minimal for several reasons: 

•-          LNG becomes lighter than air as it vaporizes & warms, so it rises & disperses.  

•-          LNG is transported and stored at near atmospheric pressure, therefore a hole in a tank doesn't propagate. Also, there is no internal pressure to spray or propel the liquid over a wide area. It's the difference between bursting a soda can and breaking a glass of water.

•-          LNG vaporizes rapidly because the surroundings are hundreds of degrees hotter than the liquid. It is very much like tossing a glass of water on a roaring campfire. The water immediately turns to steam and blows away. Same with LNG.

•-          What if the wind blows the released cloud toward buildings and people? In fact, wind helps disperse a vapor cloud by warming it and stirring it up.

            As with other dangerous liquids, facilities must be properly designed and workers must handle it with care. In that regard, an LNG receiving terminal is no more or less dangerous than an oil refinery or petrochemical plant. The big difference is that when spilled, all other fuels are heavier than air and can flow away from the site of the spill. However, LNG is more than 90% methane (natural gas) which is lighter than air. Consequently, just as a helium balloon does, spilled LNG rises and disperses as it warms. It cannot sink any more than a helium balloon can sink. Thus a spill, even a large one, is not inevitably a catastrophe, and is far less dangerous than an equal spill of LPG.

            In Indonesian Borneo, I watched a training exercise in which firemen filled a 400 square-foot concrete pool a foot deep with LNG. A mild breeze carried the white plume 30 or 40 yards downwind. A fireman walked alongside the plume to a point where he had to reach up to the plume with a burning torch to light it. He walked beside the flame front as it burned back to the pool. No explosion, no conflagration, just a large lazy flame. While a spill from a terrorist attack is likely to be much larger, the nature of the LNG won't change. If natural gas is confined and the mixture reaches explosive ratio, explosions will occur. Unrestrained, however, natural gas merely burns.

         A doomsday film "The Risks and Hazards of LNG" was shown at the Malibu Film Festival. Produced by Tim Riley, a self described "consumer protection lawyer", it is loaded with unfounded assumptions, misleading conflation of facts and flat wrong information.

            The advertising trailer opens with a scene from the first (and by far the worst) LNG accident in history in Cleveland, 1944. A small production plant, surrounded by shops and factories, produced LNG into a spherical steel tank, designed for LPG (propane) storage.  The fact that steel becomes brittle at cryogenic temperature was unknown at the time, and there were none of the safety features required in today's LNG industry, such as an encircling containment dike and set-back requirements that keep storage tanks away from plant property lines.

            A delivery truck struck the single-walled tank, which broke, spilling the entire contents into the adjoining sewer system. Because the tank was under very low pressure, there was no spray of LNG; it simply spilled onto the ground. But because there was no dike, it ran across the street into the sewer system.

           The resulting fires killed 128 people. After 60 years, this is still the only case of tank rupture, or even significant leakage. The cause is well understood, and subsequent design codes require LNG tanks to be built of alloy steel. It would be stupid of you to store gasoline in a glass container in your garage. But if you store it in a proper metal container, the risk of a disaster is very small (though still not zero). Say what you want about oil and gas people, but they are not stupid. They don't build LNG storage tanks out of steel.