In Part One we discussed the First Responder training I provided for Jacksonville Florida. Their port will be re-fueling (bunkering) several vessels with LNG that will then travel back and forth to Puerto Rico. The class was informed that LNG is the same natural gas that is supplied to homes and businesses throughout the world. One of the differences is that this gas was converted to a liquid by cooling it to -260 F. At this temperature the liquid is considered a cryogenic which simply means extremely cold.
Many of the properties that make LNG an excellent product also create hazards for First Responders. The extreme cold will freeze anything it comes in contact with. Remember, it is at -260 F. Most metals will become brittle when immersed in LNG. This could be the metal decks of the vessels that are bunkering or it could be the metal of your own equipment. Of course, human tissue will not hold up any better. Cryogenic burns resemble the burns that firefighters are accustomed to. It is actually a frostbite type injury.
The class was informed that they were not expected to be close enough to any LNG spill to worry about these burns. In fact they were given specific instructions as to just how far they should stay from a spill. More about that later in this article.
The reason the gas is converted to a liquid in the first place is to reduce its size and make it cost effective to ship. When natural gas converts to a liquid its volume is reduced 600 times. In other words, if you wanted to ship natural gas overseas as a gas you would need 600 ships to equal the same amount of equivalent gas in one LNG ship. You can see that it would not be economically feasible to transport the product in its gaseous state. In fact, prior to liquefying the natural gas it was considered a nuisance at oil wells. The gas could not be shipped in its gaseous form so it was just either burned off or released to the atmosphere.
But I was instructing a class of first responders! I needed them to know how to operate safely if there is an LNG emergency. I told them that many of the great benefits of LNG which make it beneficial to the marine community might cause problems for first responders. This volume reduction issue was one of those cases. If natural gas is reduced 600 times in size at it is converted into a liquid, what happens if there is an LNG leak? For the first responder this means that the 600 number is reversed. Each gallon of LNG that is leaked will now expand to become the equivalent of 600 gallons of natural gas. I went on to say that there are many safeguards in place to prevent an LNG leak in the first place and also to drastically limit the amount of product leaked should there be an accidental spill.
Many of these safeguards have been used in the transport of LNG which has gone on safely for many years. All of the proven safety measures would now be instituted into the LNG bunkering process.
The process of converting natural gas into a liquid is called Liquefaction. One of the first steps in this process is to remove some of the many impurities from the gas. Impurities such as water, CO2, Propane, and others would freeze and thereby disrupt the liquefaction process. The end result is that, after the impurities have been removed, the LNG is almost pure methane. As I mentioned, many of the properties which are advantageous to the LNG industry may cause problems for the First Responders. Here we found another of those problems.
Due to the lack of impurities, an LNG fire will produce almost no smoke. To prove this we lit a small dish of LNG. Smoke is actually unburned products of combustion. LNG being almost pure methane is completely consumed by the fire. Because of this the flames from an LNG fire burns hotter than a gasoline fire and therefore gives off more radiant heat. Firefighters know that this radiant heat can mean increased risks to combustible exposures. These exposures will need to be protected. In fact, the LNG portion of a small leak or fire will most likely be over by the time of the arrival of First Responders. This does not mean that there will be nothing for them to do! Combustible exposures may still be burning and any injured will still need attention.
The class was also told that LNG is colorless and odorless. These same properties apply to the natural gas that will form when the LNG converts back to a gas. Many in the class questioned this. They were sure that natural gas did have a distinct odor. We are all familiar with the rotten egg smell that is associated with any natural gas leak at a private home or commercial building to which you customarily respond. That smell is not the natural gas! It is an odorizing agent that is placed in the natural gas as it leaves your municipal gas company on its way to homes and businesses. The odorant is added so that a natural gas leak can be easily detected. However, the odorant cannot be added to the cryogenic LNG and therefore will not be present in any LNG leak. Consequently, there will be no odor.
I mentioned that the LNG is not only odorless, it is also colorless. You may have seen photos of LNG training where there is a very visible white vapor cloud. What you are looking at is frozen water vapor, not natural gas. The colorless LNG is so cold that it immediately freezes any moisture in the air creating that distinctive white cloud. It requires that moisture be in the air in order to produce that cloud. In normal humidity areas it is said that the flammable zone will be contained within the visible cloud. (DON’T COUNT ON THIS!). In fact, for safety I would say, always assume that it is possible that the flammable zone could be outside the vapor cloud. I very rarely tell my classes to assume anything! I presented numerous photos and videos to show the class exactly what that white vapor cloud looked like. The class was also warned that they, “DO NOT ENTER AN LNG VAPOR CLOUD”
Another property of natural gas is that it is lighter than air. When it rises into the atmosphere it is no longer a problem for the first responders. But that is for warmer natural gas. At an LNG leak, prior to it warming up to warm and toasty -77 C (-170 F), the colder natural gas will hug the ground. It will then travel down wind and, if it finds a source of ignition, it will burn back to its source in what is described as a lazy flame. It will not explode in the open however, if confined, like in a basement, it may burn explosively. (Remember, it is natural gas!)
The class was informed that you cannot assume that this visible white cloud contains the boundary of any flammable vapors. Also, everyone in the classroom heard me state at least 20 times during the class that they “DO NOT ENTER AN LNG VAPOR CLOUD”. I don’t even want you near the cloud. Immediately hands were raised in the class. “If the flammable portion is outside of the visible vapor cloud, how will we know that we are near the flammable vapor cloud?” My next slide showed some equipment that is already carried on many of the first responders vehicles that would answer this question. CGI or Combustible Gas Meters have been used by Fire Departments for many years.
The class was told to use their own meters so they would be familiar with them. (Always use your own equipment whenever possible.) I also said that they should go no closer to the leak than 10% of the Lower Flammable Limit (LFL) as indicated on the meters. That point should mark the start of your “Hot Zone”. Again,…..
“DO NOT ENTER AN LNG VAPOR CLOUD”.
Natural gas has a flammable range of 5% to 15% in air. This means that below 5% it is too lean to burn and above 15% it is too rich to burn. We want to keep any and all sources of ignition from coming in contact with that 5%-15%.
Many sources of ignition are obvious. An open flame, cutting and welding operations, lighted match etc. But there are other sources of ignition you may be bringing with you. Your fire apparatus and vehicles have a internal combustion engine. Your portable radios, even the combustible gas meters we mentioned before has a battery which may create a spark if the unit is not intrinsically safe. Your fireboat or other passing vessels in the area may ignite the vapors if they get too close. No one should enter the area without a combustible gas meter and then go no further than 10 % of the LFL. And guess what, “DO NOT ENTER AN LNG VAPOR CLOUD”
There were many more properties of LNG and tactics which were discussed. I am not able to cover everything that first responders need to know in this article. Remember, even if you are not located along the water you may still have to deal with an LNG emergency. As mentioned, buses, trucks, locomotives, and construction equipment may be powered with LNG in your response area. And don’t forget, these vehicles will need to fuel up so you may have an LNG filling station along your roadways and rail lines. LNG may also be being transported through your district in tanker trucks and rail tank cars. You may want to consider some LNG training of your own!
At the end of the class, even with all of the hazards associated with LNG the participants were shown that if they are aware of the hazards and also aware of the tactics needed to mitigate those hazards then an LNG emergency can be handled safely. Knowledge and Training is the key.
And remember…… “DO NOT ENTER AN LNG VAPOR CLOUD”.
For more information, go to www.marinefirefighting.com