A Challenge at Hand Fire Protection in the Age of Missiles
THE AUTHOR graduated from Cornell University in 1931 with a degree in electrical engineering and in 1948 received a Master’s degree in chemical engineering from Columbia University. A registered professional engineer and a member of the Society of Fire Protection Engineers, he joined the U. S. Fire Protection Engineering Service. Inc., Kansas City, Mo., in 1957 as a senior engineer, initially participating in a worldwide survey of U. S. Air Force fire protection problems. His experience includes service with Esso Research and Engineering Co., E. I. duPont de Nemours and National Aniline and Chemical Co.
THE ACE of scientific fiction come true is upon us and with it has come a new dimension in fire protection. Not too many years ago, the idea of traveling around the world in 80 days was considered nonsense. Those “in the know” said it couldn’t be done. Air Force planes now accomplish this in half the number of hours and the feat arouses only momentary interest.
Author Jules Verne wrote Twenty ‘Thousand Leagues under tlw Sea as a scientific novel. As far as he knew, it was simply an exercise in literary imagination. Recently the submarine Nautilus made this story seem like a prophesy at first, then far exceeded it.
Since the first Russian Sputnik was hurled into orbit late in 1957, we have learned to accept as routine the satellites which have since been launched. Every few months we read of another step forward in the conquest of space. All the satellites have carried radio telemetering and Atlas, the flying chatterbox, was the first space radio relay station. It was a major communications achievement, but only for a few days did it receive headlines in the newspapers. The marvel of today is commonplace tomorrow as the novelty of such things fades quickly. Learning how to live with them takes far more time.
Scientific advances such as these have required the harnessing of tremendous amounts of energy. What we have already witnessed is just a start. As surely as tomorrow follows today, man, spurred on by military and competitive rivalry, will utilize greater and greater concentrations of energy in his conquest of space. Along with this massing of energy will come many serious hazards which we are currently unprepared to meet. At present, we have neither the attitude nor the tools.
New methods needed
Judged by the progress which has been made in other fields, fire protection is still in the horse and buggy age. We still rely on overpowering fires mainly by sheer weight of water. For ordinary combustibles this works, and works well, and our protective system is based upon it. Often the water damage may exceed the fire damage, but this has to be accepted along with the basic brute force technique.
The most common sort of fires have not changed in their character over the thousands of years man has been civilized. More people are burned to death now, and more property is destroyed, hut the burning of paper, wood, and cloth is the same as it always has been and it can be expected to remain so. The need is not to junk what we have but to modernize it.
Fires not average
The fires we must learn to cope with in the developing missile age are not what we can consider average. They involve greatly increased concentrations of flammables, and many variations in the way they burn. In some cases, the uncontrolled energy release far exceeds the capabilities of any extinguishing system we can provide. We must face the dangers of violent explosions in fire fighting. Some extinguishing agents give off toxic gases when decomposed by the heat of fires. Others react with the burning material and create a new hazard by their use. One new propellant fuel is so toxic that the small amounts absorbed by water in contact with it may seriously contaminate areas well beyond the fire zone.
All nuclear applications are carefully engineered to “fail safe,” hut if a fire occurs, heavy metal vapors may be almost as dangerous as a small nuclear explosion; radiation exposure is always a potential factor. So far, our technology has been concentrated on new accomplishments. We now need the same high calibre of effort in dealing with the hazards these accomplishments have brought with them. We must develop far more than new ways to squirt more water!
Just what form this needed effort will take is uncertain at the moment. Basic fire research is hampered by a lack of obvious, definite things to research. The problem is so broad that most of the fundamental work to date seems only to nibble on the edge. It is complicated by the extremely variable nature of fire itself. Since tangible results are difficult to promise, the research dollar is often directed elsewhere.
In safeguarding life and property, we are not overly concerned with ordinary combustion, where fuel and some oxidizing agent (usually air) are brought together under controlled conditions and the heat released is used as intended. What really concerns us are the unexpected situations where something which will burn escapes and catches fire under conditions with which we are unable to cope.
To study such fires, we must reduce the unexpected situation to a routine one so we can duplicate conditions. The problem may be compared to studying a wild beast without making it tame in the process and destroying its character. We cannot rely on always being able to overpower a fire. The real solution is to discover its weaknesses, then effectively attack them.
Years ago, when the popularity of the automobile started the petroleum industry on its phenomenal growth, the storage of gasoline and other oil stocks in large quantities created a very real flammable liquids hazard. That was met by the development of chemical foam and application techniques. We now have mechanical foam plus the knowhow to use it effectively, and the storage of petroleum stocks in reasonable amounts no longer constitutes any unusual problem. This is not to say that the fire risk has been removed from the oil business. The storage and handling of flammables is never completely safe from human error, so some fires must always be expected. With foam as an effective weapon, however, the petroleum fire need not be the scourge that it was once considered.
Fire fighting foam is simply a sophisticated and highly efficient way of cooling and smothering a fire. Some may wonder why the same approach cannot be used for the propellants used in the missile field. The answer lies in the extremely reactive nature of such fuels and the concentrated energy they represent. Mixed in exactly the right proportions, the fueloxidizer combination must operate in a very simple engine, deliver a tremendous amount of power, and drive the missile faster than an artillery shell. In effect, a missile launching is a carefully controlled explosion. Once started, explosions are difficult to stop. If control is lost, there is little or no time to do anything about it, and little which can be done.
Water and personnel problems
The classic fire triangle thinking teaches us to cut off the supply of fuel, to cool below the ignition temperature, or to cut off the supply of air. The first will always work if it can be accomplished. The second is often attempted, but such large quantities of water are required in such a short time to be effective that inertia is a real factor. A rocket engine testing site, for example, might require a water flow of 30.000 gallons per minute. A flow of this magnitude takes time to establish.
Unless water is flowing before the fire, all the damage might be done before water could be made effective. Starting the water is part of count-down procedures and certainly the missile stand is protected at the expected point of flame impingement. If, however, the missile topples or falls back in a misfire, the chances of using the main water supply are pretty small. There just aren’t enough hose lines and men to put 30,000 gpm into a given spot in the time available. At present, damage to the missile has to be accepted. The only safety to personnel lies in distance and concrete bunkers. When we reach the point in our rocket progress of carrying humans, something in the way of rescue will be needed.
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Let us consider the matter of cooling requirements as affected by the fuels involved. Ordinary combustibles release about 8,000 Btu’s per pound when burned. Every pound of water applied to a fire can absorb up to about 1,000 Btu’s of this heat, so cooling an ordinary fire is no great problem. Once the temperature goes below the kindling point, out goes the fire. When we consider flammable liquids, which average around 18,000 Btu’s per pound heat release, things become more difficult. Applying water as foam takes full advantage of its heat-absorbing properties, so that again we can effectively break the fire triangle. This time we say we cool below the flash point of the liquid.
High energy fuels
The new fuels pack a lot of wallop because missiles need energy at a minimum weight. Their heating values start around 25,000 Btu’s per pound and go on up to almost twice that. No longer arc we dealing with flame temperatures of about 1,500°F. The theoretical combustion temperatures of various fueloxidizer combinations are in the range of 4,000-7,500°F. Under such conditions, no materials can last very long. The useful life of structures exposed to such heat is measured in seconds. Rocket combustion chambers can be built to withstand terrific heats for their extremely short useful life, but when things go wrong, the fire may be anywhere else. Inside of moments, a sleek airframe may be a tangled inferno of raging flames. It should not be impossible to deal with such fires hut so far, we have no solution.
We know that some metals such as sodium, react with water and therefore many metal fires cannot be attacked with water. To some extent, the same is true with certain of the new fuels. Applying water as spray, or as foam, to such fires will he of little practical value.
For example, liquid oxygen used in many large missiles forms shock-sensitive explosions when mixed with fuel. If tanks are ruptured in a fire, the unburned mixture may detonate from the impact of a hose stream. This is not just a theory! Such explosions have already been experienced in development test work.
In addition, most rocket fuel-oxidizer combinations will operate in the vacuum which exists outside the earth’s atmosphere. Once ignited, they continue to burn regardless of any cutting off of the air supply. The third side of the fire triangle is meaningless under such conditions.
We must not take too dismal a view of what difficulties may arise in making the space and missile age fire safe. Many people have worried about the dangers of carrying nuclear weapons in flights over our own soil and that of friendly countries. The built-in safety of atomic weapons has now reached the point where aircraft so armed have crashed and burned without a nuclear explosion.
The same inherent degree of safety can probably be incorporated into practically all today’s scientific accomplishments which now present a major fire or explosion hazard. It will not be easy. Protecting mankind from the unforeseen consequences of his new techniques will require a new look in fire protection. We must look into the future, rather than back to the past. Going places is now more important than knowing where we have been for centuries. We must rely on science and engineering as the basis for decisions rather than unsupported opinions. Relying on past experience will be valid only for similar situations. For what we are facing, there is no experience!
In the past, fire fighting has required a mixture of courage and brutally hard work handling hose streams. Tomorrow we will need more courage, more brain power. Unless we can develop new apparatus. there will still be hard work to do, but we can no longer rely on muscle power alone to do what must be done.
Until we recognize that a problem exists and requires our utmost technical resources, we shall probably continue to plod along as we have done in the past, putting out fires as we come to them. Stating this fact is not taking a gloomy attitude about the whole business. We humans always take the course of least resistance, changing our ways only when we are forced into it, and then unwillingly. We can do the same with the fire problems about to confront us, ignoring them as long as possible, then working in frantic haste to find a way out while we suffer from our follies.
That is the path of complacency. The price of following it in this new era will be paid in human lives and property loss, a toll even greater than we are experiencing today. We cannot fail to wake up to the challenge and develop the knowhow to prevent catastrophes from happening. For unless we do, we shall surely be faced with them! □□