Essentials in Handling Large Oil Fires
Conclusion of Paper on This Subject—Improvements in Fire-Banks— The Foam System of Extinguishment—Protecting Fuel Oil Plants
THIS paper, which is concluded from page 37, FIRE ENGINEERING, January 10 issue, is the result of careful study and research into the origin, peculiarities and methods of fighting fires in oil tanks. It is full of practical suggestions for the fire chief who has this problem to wrestle with:
Improvements in Fire-banks
The most serious menace from a crude oil fire comes when it boils over. If the boil-over can be held within prearranged firebanks, there is no further difficulty; but fire-banks have not always proved effective, and we therefore turned our attention to the possibility of improving fire-bank design. Here again we turned to small model apparatus, as tests on full size tanks with fire walls would have been impracticable. We therefore set up the apparatus shown diagrammatically in Fig. 8. A segment of the “tank” from which the “boil-overs” were discharged is shown, and model walls of various sizes and shapes were set up—the whole outfit being made to a scale of about one inch to the foot. Altogether in these tests we made some 66 of these walls, and allowed 1,000 miniature boil-overs to flow against them. These tests showed that all the present types of wall could be vastly improved by the application of the old sea wall principle of folding the advancing waves back on themselves.
F’ig. 9 shows the comparative height of different walls which will fully retain the same spill. A one foot vertical wall with a coping is as effective for turning back the wave of oil from boil-over as a four foot plain vertical wall or a five foot earth dyke with a slope of 1 to 1, or a seven foot earth dyke with a slope of 1 1/2 to 1.
Fig. 10 shows a number of practicable methods of applying this principle. That this principle is not just an experimental theory was demonstrated soon after the tests by a fire in one of the California fields, as shown in Fig. 11. A tank of crude burned and boiled over, the tank being distant 160 feet on practically level ground from the company’s wooden frame pumping plant. By building temporary earth fire walls topped with a flare-back of corrugated iron, the station was protected from ignition.
So much for the tests that we have conducted with the view to increasing our knowledge of behavior of burning oil tanks and protecting against spread of fire by boil-overs.
The American Petroleum Institute made in the early part of this year a very comprehensive survey of the records of all oil fires that have occurred in the United States during the past ten years. I believe that this is one of the most thorough investigations of fire records that has ever been made in this country, and it has yielded some very interesting results. The entire report has been published, and any of you can obtain a copy by addressing the American Petroleum Institute in New York City.
Contributions to Knowledge of Oil Fire-Fighting
There have been several other contributions in recent years to the oil industry’s knowledge of fire protection. Summarized, the more important developments have been—
Fire resistive oil storage tanks.
- Tank appurtenances which minimize fire hazards.
- Recognition and elimination of fire hazards.
- Knowledge regarding the behavior of oil fires.
- Fire walls of a design which will more effectively control a flow of oil.
- Effective oil fire-extinguishing systems.
Going into a little more detail regarding these developments, we can say that a modern oil tank, properly equipped, is very fire resistive. Many cases are on record where flames from exposing fires have enveloped tanks containing gasoline without damage to tank or contents.
The modern all-steel tank has an excellent fire record as regards lightning, and is believed to be immune from the lightning hazard. This is important because statistics show that 55% of the oil-tank fires in the last ten years were caused by lightning.
Static electricity has been blamed for many oil fires, and has quite likely caused several. During the last few years knowledge has been gained regarding static phenomena, and practices have been introduced which tend to protect oil risks from this hazard.
We have learned what to expect when an oil tank is on fire. We know now that if a tank contains a refined oil (gasoline, kerosene, distillate, etc.,) and is ignited, it will burn quietly until it is extinguished or the contents entirely consumed. There is no danger of an explosion or a boil-over which will force the oil out of the tank.
Protecting Fuel Oil Plans
In the case of fuel oils, which arc usually the only other oils found in cities, we know that there is a possibility that the oil will ultimately boil out of the tank if the fire is not extinguished within the first few hours after ignition. We have learned, however, to fairly accurately predict the time when we may expect a possible boil-over, so that we can utilize the time before this boil-over to prepare fire walls, etc., to control any flow of oil, and to take the necessary precautions to avoid anything from being endangered by the flow of oil from the boilover. As a matter of fact there is little likelihood of. the occurrence of a fuel-oil fire. Most of the fuel oils have a flash point above 150° F., and it is extremely difficult to ignite a tank of fuel oil with paper and matches.
Progress in Extinguishing System
Considerable progress has also been made in developing effective extinguishing systems for oil fires. Fire records show cases where tanks containing 80,000 barrels of gasoline on fire have been quickly extinguished with foam systems. These tanks are 120 feet in diameter and 40 feet high, and when we consider that at the surface there are over 12,000 square feet of gasoline burning at one time, it shows that the method of extinguishment is quite effective.
The details of many of these problems are more for the fire protection engineers of the oil companies than for the fire chiefs, who have no time for anything except high lights on the subject. Probably what the fire chief is principally interested in is how to prevent these fires, and what he can do to more effectively combat a fire of this character. I will therefore briefly discuss these two phases of the subject.
Fire prevention in the oil industry is largely a matter of proper construction detail; although, of course, good housekeeping is Essentials in Handling Large Oil Fires of paramount importance here, as in any other industry. Details of construction involve a special engineering study for each case. This study combines safe structural practice with knowledge gained through experience by the oil industry regarding the hazards incident to the commodities handled. Tank construction has been greatly improved in the last few years, but to show that the type of tank which has been in use during the last ten years has been a relatively good fire risk. I will give you some statistics from the survey of the American Petroleum Institute. In oil marketing stations, which arc usually the only oil plants found in cities, it was found that out of a total of over 11,000 there have been less than two fires per year. This is equivalent to one fire every 5,860 years for each plant, or in other words there is one chance in about 6,000 of any one particular plant catching on fire during a year’s time.
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As for fire protection—it is difficult to outline definite suggestions for municipal fire departments’ aid in fighting fires in oil plants. It is always a good idea for the fire department officials to occasionally visit each large plant, and have a talk with the superintendent who can assist in outlining a method of procedure and cooperation in case of various contingencies. Where there is a foam system, the fire department can sometimes help with the operation of the system. This is particularly true in cases of fires at night where there may be but few employees at the oil plant, and where the operator of the foam system can be considerably helped by efficient aides.
The Foam System of Protection
For the benefit of those unfamiliar with the foam system, it will perhaps be well to bring in here a brief description of the foam system of protection.
Experience has shown that when a fire resistant froth is floated on top of a burning oil surface the heat of the flames is cut off from the oil surface. As the oil surface cools, its vaporization is decreased so that the flames soon die down from lack of fuel to feed them.
To produce a proper froth for this purpose, two chemical solutions are mixed together in equal proportions. These solutions are stored separately, one in each tank. In order to prevent the foam from being broken down by mechanical agitation before it reaches the fire, it is desirable to bring the solutions together as near as possible to the oil surface where they are to be applied. In practice separate pipe lines are usually run to the oil tank protected by the foam system and the lines are siamized into a mixing chamber at the edge of the oil surface. Here the foam is produced and allowed to flow over the oil surface.
The solutions are supplied in proportions as nearly equal as possible by means of two pumps of the same size and operating at the same rate of speed.
Where a hose stream is desired two hose lines are used—one for each solution—and the solutions brought together in a short length of a larger sized hose siamized to the twin solution lines. A nozzle is used on the end of the short length of single hose, and the foam stream controlled as any other fire stream.
Fire Apparatus as Temporary Foam Pumpers
The fire department can sometimes provide pumping facilities in case the foam pumps are, for some unforeseen reason, disabled at the time of the fire, or in case foam solutions are available where there is no foam system. Chiefs Short and Scott have both had occasion to call upon their departments to function in this way. (See Fig. 12.)
When the fire department pumps foam solution with its regular pumpers, best results arc obtained if positive displacement pumpers (rotary or plunger) are used. These should be preferably of the same type and rating, and should be run at the same rate of speed. It is best to take suction from the top manholes of the solution storage tanks, if sufficient suction hose is available, otherwise the oil companies can probably make some kind of pipe connections for getting solutions to the pumpers.
The fire department can furnish hose lines to replace pipe lines in case the foam solution lines should become broken or otherwise be out of commission, or in case an extension is desirable.
How to Use Foam Hose Streams
Foam hose streams are often used to supplement regular foam mixing boxes on tanks, or for extinguishing pools of oil on the ground. A foam hose stream is used effectively in a different manner than a water stream. The foam should not be directed into the oil, nor should it be sprayed around over the oil surface. Best results are obtained if the stream is impinged against some vertical object, and the foam allowed to float quietly over an oil surface. In extinguishing a tank fire with a foam hose stream, if possible, direct the stream across the flames to the other side of the tank shell, attempting to hit the inside of the tank shell above the oil surface, thus allowing the foam to flow on to the oil surface where it will spread itself across the fire. I have seen instances where the oil surface was almost covered with foam and the fire practically out, when careless handling of a foam stream swept the foam off the surface, and allowed the fire again to flash over a large part of the oil area.
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Essentials in Handling Large Oil Fires
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In directing a foam hose stream on a pool of oil on the ground, the same method should be followed as in covering the oil surface in a tank with foam. Where there is no wall or other object alongside the pool against which to direct the stream, it is best to hit the ground at the edge of the fire. The foam which is thus formed on the ground is pushed by the stream onto the fire.
When it is desired to apply foam to a tank not equipped with a mixing box, or on which the box has perhaps been put out of commission by the collapse of the roof or some other cause, we have found a portable mixer, as shown in Fig. 13, to be very useful. The tube is made of a light strong alloy so that it can be easily carried to the tank and up-ended on the rockers provided at the bottom by a few men.
Fig. 14 shows a test fire in a 30′ tank in which various types of mixers, including one of these portable types (indicating), are being tried out. On this matter of foam protection, our Company has done a large amount of experimental work to determine the proper rates and methods of application to tanks of various sizes; the most effective formula for the two chemical solutions, etc.
So much for the use of foam in fighting oil fires. Water should never be used on the same fire with foam because the foam is broken down by the water. The effectiveness of foam is greatly decreased when a little water is sprinkled on it. The shell of a tank to which foam is being applied, can, however, be cooled with water, and a tank thus cooled can be extinguished with less foam and in shorter time than where the shell is not cooled. This is particularly true with high vapor pressure oils, such as gasoline. The drainage of water must be watched very carefully around an oil fire to prevent spread of fire by oil floating on top of water.
These are some of the more important special features connected with the work of fighting oil fires. I will not take time to discuss any more, for it is likely that you will have some questions to ask and I will welcome a general discussion of this subject for the remainder of the time allotted me. To sum up briefly the message that I have tried to bring: During the past few years we have emerged from uncertainty to quite definite knowledge of what is required for safe oil storage construction. We have learned that a properly constructed gas-tight steel roof tank, containing refined oils, has an excellent fire record, and is relatively a good risk.
As for fire fighting, we have, through extensive experiments and actual experience at fires, learned about what is required to make most effective use of both foam and water. I have tried to point out how the local fire departments may be of great assistance to the fire fighting organizations of the different oil companies when fires occur.
In closing I wish to say (and I am sure I speak for the fire protection engineers of the other oil companies as well as for myself), that we invite the cooperation of the fire chiefs in an effort to keep down the fire loss record. We will be glad to work with them at any time on such of their problems where our specialized knowledge can help.