Preventing Fires Involving Petroleum Products
THE first principle of fire protection for oils is to store them in good tanks. You should be able to tell whether or not an oil tank is properly designed and constructed. If it is, half your problems are over; if not, you should know that your secondary defense against failure lies in dikes and vents. Dikes are designed to lake rare of spills and overflows, as well as tank failures. Vents are designed to relieve vapors when filling and emptying tanks. But vents are also safety valves in case of exposure fires and you should know how big they should be for each type of tank and especially for tanks that don’t have weak roofs.
Recently at a fire at a bulk plant in the State of Washington there was some outside spread when one of the horizontal oil tanks took off like a rocket. Not long afterwards there was one like it in California. Now neither of these fires would have been serious except for the behavior of the tanks when exposed to radiant heat. As a matter of fact, the two fires were identical in this—that the tanks were not provided with proper vents.
The matter of diking has always been a difficult one to understand. The basic rule is that if escaping oil can get out of the property and do damage to others, some means must be taken to keep it at home. Out in the desert or even at the edge of town, tanks need no dikes. On the edge of a stream that later flows through a city, they do. There are a variety of other conditions that may govern.
What has been the principal difficulty has been an old Underwriters’ rule that said that when a dike was built it had to provide capacity for all of the oil in all of the tanks, if they were all full at the same time. That rule is fine for one tank but is absurd and unnecessary for a group of tanks. It is as unreasonable as requiring a bank to keep on hand in cash all of its deposits. Experience teaches how much money a bank must keep on hand and experience has demonstrated how much capacity a basin must have to take care of oil tanks.
Another problem of all ordinance writers has been that of tank spacing. No two engineers in the country can tell you how far from each other or how far from the nearest property line it is safe to place an oil tank. The reason is that distance is not the important or governing factor. If the tank is well designed and well built, it can be within ten feet of the property line and not endanger its neighbors. Similarly, a group of tanks standing in a single row can be three feet apart, and be reasonably safe. The problem is one of preventing oil tanks from being unduly heated in an exposure fire. Hence the spacing should be such that you can get cooling streams on them without putting your hosemen in jeopardy. The next time you are asked to approve an oil tank layout, think of it as a problem in cooling down an exposure, not as a problem in suppression. You may never have the chance of fighting an oil fire in a tank but you will have many structural fires where oil tanks are exposed. And if you do have an oil tank on fire, let it burn out. There is no fire that is so well behaved or that will cause you less real trouble.
Fire experience has taught us that there are two types of fires at marketing stations that seem to repeat. One type involves warehouses and the other loading or unloading spots for tank trucks. Now the Uniform Building Code requires fire resistive construction for oil warehouses whereas the custom of the trade has been to build them of galvanized iron on wood frames. The reason for this wide difference in point of view is again experience vs. theory. In an oil storage warehouse you have cases and drums of flammable liquids, plus the usual hazards of wood cases, etc. If a fire gets going in such an occupancy, the chance of extinguishment is practically nil. even with chemicals. However, the chance of holding the fire within the four walls is about one hundred percent if you can get fog streams on it to take up the radiant heat. It has been our experience that galvanized iron exterior and roof will prevent spread into the warehouse and that a wooden frame will burn down and let you get at the burning contents better than any other combination.
As to loading and unloading spots, good engineering requires that these be so spaced that you have twenty-five feet around the vehicle being worked on. Fires start from a variety of causes and no spacing formula will prevent an occasional fire when handling gasoline into or out of a truck.
What you are concerned with is suppression and that requires that you have fighting space within which to bring up your cooling streams or fog sprays.
Another consideration is drainage. Wherever gasoline and other liquids are handled by hose there will be hose failures and occasionally an overflow. If proper drainage is designed into the layout, you will have a lot easier job when you arrive on the scene. Proper drainage means getting the spill away from surrounding structures and if possible from under the vehicle. Each plant is a separate problem, hut the principle is the same in every case. Just picture to yourself that there has been an overflow or a burst hose and see where you want the spill to go. You can assume that there will be many such without any ignition but eventually one may take fire. Where do you want that fire to be. under a building or off to one side where you can handle it?
You may ask why the fire chief or fire marshal should be an oil plant designer. The answer is that more than half the plants in the country are engineered by people who know less about the job and don’t have the fire chief’s interest in fire prevention.
As to service stations, there is little that is new. We believe that all underground tanks should either bear the label of the Underwriters Laboratory or be built to equal standards. The size of the tank and the number at a station is not of any importance from the fire standpoint, and yet more laws have been written on that subject than any other in the oil business. Fortunately for the oil companies, they haven’t limited the amount of gasoline that a station can sell in a day. Hence we have stations that have to be served by the oil truck once a day whereas in other cities once a week is often enough.
Outside of the quality of the tanks themselves there isn’t much to worry about in a service station except to see that the vents are adequate and don’t have screens in them. The old regulation requiring screens was based on the assumption that fire would go down a vent pipe. The Underwriters Laboratory found it wouldn’t and that is also proved by all our years of experience. We do not want screens because they catch dirt and spray paint. The vent should be so free that no vapor is spilled at the fill opening to the underground tank when the tank truck makes its dump. The size should not be less than 1″ pipe or if there is a long run, 154″.
Every so often some fire chief or inspector becomes concerned about the use of open flame heaters or stoves in service station buildings. I am sure that if there were some safer way to heat these little rooms where the attendant stays between jobs, we would all welcome it. However, none has so far been presented and so we must deal with the situation realistically and not theoretically. First, let’s look at the record. What actually causes fires at service stations? The combination of matches and vapors of gasoline is the greatest source of fires. Very seldom do you have fires from this cause while a car is being serviced; occasionally you have a fire when a truck is making a dump. That is when a lot of vapors are being pushed out of the underground tanks. If the vents are plugged with wire gauze or are inadequate, vapors also pour out at ground level from the fill opening into which the hose from the truck is pouring its stream of liquid. These vapors are heavy and will drift around the station yard if there is no wind. A match tossed on the ground will of course cause a fire. Hut if the driver is at his proper post and not in the station building or wandering around, he can stop such a fire at once by simply turning off the valve on his truck. Some fires have occurred at the vents on the sides of buildings when vapors pouring out during a filling operation have been lighted by smokers coming out of the rest rooms. But so far as we know, there have been no such fires started by heaters in stations. There have been inside fires caused by heaters when attendants have used or dispensed gasoline inside the station office.
So, our best advice is, keep gasoline out of the office and let the boys have their heaters. If they cause no more fires in the future than they have in the past, there is nothing to worry about.
Liquefied Petroleum Gases
If you were to look at the definition of a flammable liquid in almost any code, you would find that it included butane and propane and yet you could not apply the code to these gases. 1 he new code will be better worded, as the liquefied petroleum gases (which we call LPG for short) now have a code of their own.
Some cities have adopted by reference or otherwise the National Board pamphlet No. 58 for the regulation of LPG. That pamphlet was first put out many years ago, when these gases first came on the market and it was the best information available at the time. Now it is as out of date as any other piece of old machinery in this fast moving age. For that reason it has been completely revised and reissued under the same number but dated the first of this year. The new edition is the best regulation available at this time and anyone who is using the old pamphlet should immediately throw it out in favor of the new one. It is not an ordinance but can be used by reference as a standard for design, construction and operation of LPG installations. Already many states have adopted it.
The main difficulty that we have experienced with LPG has been with the people who handle it. Few of them are well trained in handling hazardous commodities and yet they presume to handle the most dangerous material on the market today. Actually, more damage is done by the misuse of LPG every day than by dynamite and yet few states or cities require any certificate of competence on the part of installers or handlers. We believe that a state act administered by the State Fire Marshal and backed up by the fire prevention bureaus of the cities is the only way to control the situation. In California the Industrial Accident Commission has tried to handle it and has made a complete failure of it because they think in terms of pressure vessels and not of fire. Actually, very few LPG tanks tail; it is people who fail in handling LPG. Hence only fire prevention men who know how to deal with people can ever control this type of hazard.
I have in the past years investigated many LPG fires. All the serious ones resulted from the escape by accident of large volumes of gas which were subsequently ignited. In such a situation you can have outdoor explosions and you always have terrific heat along the ground. People caught in a vapor cloud of LPG when it ignites are always killed because the human body cannot stand three thousand degrees of heat even for an instant. Unfortunately the codes have not yet recognized the fact that it is the formation of these vapor clouds that make the greatest danger from LPG. If they did recognize this fact, you would not see signs on LPG tanks reading “Keep open flames fifty feet away.” The safest thing that can be done to any LPG installation is to have a pilot light near the ground level as close as possible to the tank or place where the LPG is transferred. Then if there is a leak it will be lighted at once and will simply burn as a torch, without danger to anyone.
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This is not as crazy as it sounds. There arc many large commercial installations where there are open flame vaporizers right alongside of the tanks and they have operated more safely than all others. Then there is a system of home butane service used in Texas, where there is a skirt built around the butane tank that -its next to the house being served. Inside the skirt and under the tank is an open flame burner that keeps the tank warm. When the demand for gas increases, the flame goes up and provides more heat. There have been no accidents with many thousand such installations.
What all this boils down to is this: if a plant is well designed and operated it can have open flames within five feet of the tank, pump and dispensing unit. If it isn’t that well put together or operated. it isn’t safe under any conditions and you should not allow it in your town.
I have had some correspondence lately about old gas plants and systems that have been converted to LPG. You have a real problem there, because the old lines have corroded and the new gas, being a solvent, finds all the holes and gets into the ground. There is onlyone cure—pipes tiiat don’t leak. However, tile hazard isn’t too serious or we should have had a lot more fires than have been reported. Actually, we have the same situation every time natural gas comes into a town for the first time. My advice is, be sure the gas carries a lot of skunk oil. Without it you cannot detect leaks. Lines should be tested frequently during the first year, since that is when leaks develop from the solvent action of the gas on the tar in the lines. Some companies inject steam into the lines with the LPG in order to rust up pin hole leaks.