PREVENTING TANK EXPLOSIONS DURING RESCUE OPERATIONS
Use of Fog Suggested as a Means of Checking Development of Explosive Conditions
THE article “Explosion of ‘Gas’ Tank Car Kills Three and Injures Eight” appearing in the October, 1943, edition of FIRE ENGINEERING raises a thoughtprovoking problem for the earnest consideration of the Fire Service. The disastrous incident reported by Chief Waldo Merrill of the Council Bluffs, Iowa, Fire Department, in which three men, including Fire Department Driver John Peterson, lost their lives, and eight others were seriously burned or injured, was the result of an explosion occurring while rescue of an unconscious mechanic was under way inside an almost empty gasoline railroad tank car. Driver Peterson with oxygen mask removed but still affixed to his body, was steering the body of the victim into the dome when the explosion or flash fire occurred.
It is the opinion of Chief Merrill that the flash fire was caused by a spark from an unknown source and not by static .electricity. The Chief further stated, “If this condition should reoccur, I can see no method than what was done, other than to render a silent prayer and hope that there will be no explosion until the rescue is completed.” Just so long as there is no regulation against entering a tank before it is freed of flammable vapors or a workman carelessly jeopardizes his life in recovering a dropped wrench from such a tank, a like tragedy can strike any Department of the Fire Service at any time with more or less devastation than the fateful happening in Council Bluffs. Because of this the writer offers this paper as a second discussion in what might be termed a round-table debate which he trusts will stimulate interest, interchange of ideas, definitely channeled laboratory tests and the ultimate production of absolute preventive measures. The first discussion can be considered as having been given by Lt. Walter B. DeBoer of the Denver. Colorado, Fire Department, who, in a letter to the Fog Nozzle Company of Los Angeles, California. advocated the use of water fog as a medium to reduce by dilution the vapors below the explosive range. The full text of Lt. DeBoer’s letter is:
“In reading the October issue of FIRE ENGINEERING magazine, I came across an article which, I believe, should he of interest to both your company and to all firemen.
“The name of the article is ‘Explosion of Gas Tank Car Kills Three and Iniures Eight.’ (It appears on page 633.) In this article it tells the story of what was done and ends with this. ‘If this condition should re-occur, I can see no other method than what was done, other than to render a silent prayer and hope that there will he no explosion until the rescue is completed.’
“My contention is this: Had a . . . (fog nozzle.-—Ed.) been used to cover the inside of the tank car for a brief period and then held as a protective cover over the dome, there would have been no explosion. First due to the greater humidity created inside the tank car and second due to the dilution of the vapors present both inside the car and outside would have made an explosion practically impossible. The rescuer was protected from asphyxia with the self-contained gas mask and had he had this other inexpensive protection he would probably be alive today.
“It is not my intention to point out the defects in the procedure of this fire but to point to a solution of a problem which has been stated as almost unsolvable. We can all ‘second guess’ very nicely and tell how we would have done, but had we been on the spot at the time probably would not have done as well. We can, as firemen, offer soliutions to these problems as we see them, or at least attempt a solution.
“I must admit, in fairness, that I have never had a like situation, but through study the above answer is an answer to the problem and I think that your Company could make an experiment and prove the point.
“If you think any of the above has merit, feel free to use it but I do wish you would inform me of your findings.”
The Lieutenant’s letter was referred to this Department for consideration and report on the practicability of water fog, no doubt because of the Department’s universal adoption of water fog equipment. To amplify this statement it may be said that the Department pioneered in the development and acquisition of water carrying fire apparatus. Every one of its more than ninety pieces, from a 2500 tank capacitv behemoth with its large fog applicators to the 70 gallon tank capacity half-ton Pickup Patrol car with one inch fog nozzle, is fully equipped with water fog appliances to assure the water supply lasting longer; to make extinguishing efforts more positive with increased personnel safety; and to reduce water damage by fog application. Knowing the proven effectiveness of water fog on structural, oil or forest fires, the writer was immediately in agreement with Lt. DeBoer. However, for the purpose of this discussion, it seems wise to (1) consider certain happenings at the disaster from information contained in Chief Merrill’s reports; (2) set forth possible direct or contributing factors as to the cause: and (3) list measures that might prevent a similar disaster.
1. Happenings at the disaster: Significant was the fact that tne temperature was around 91°, and relative humidity some 38% at 5 p.m., the approximate time of the explosion. Such a relatively low humidity in the climatic conditions encountered in the middle west would be conducive to the building up of excessive static electricity charges with the high temperature nullifying any formation of condensation on the interior tank surfaces which, if present, might have effectively drained off a considerable degree of the static charge.
A particular point of interest was the action of Driver Peterson in removing his oxygen mask apparently in order to negotiate more easily the opening in the baffle plate, or to effect clearer vision.
The question naturally arises, “Did Driver Peterson close the valve at the mask or was the oxygen allowed to flow?”
The small 15-inch diameter opening into the dome made it practically impossible to avoid contact between it and the rescued person’s body. Whether the rope used to hoist the body was clear of the metal surface at the time of the explosion, is not known.
It is reasonable to assume that Driver Peterson entered the tank shod with leather soled shoes and whether he had donned a turnout coat is not known, but it seems doubtful this would be the case because of the high temperature.
Chief Merrill very well stated that the rapid heating of the victim’s clothes as the body was raised into the dome space would result in immediate change in the gasoline vapor percentage.
Direct or Contributing Causes
2. Possible Direct or Contributing Causative Factors: (a) Oxygen escaping from mask inside of tank creating explosive mixture which could ignite spontaneously. Such a cause is possible, but improbable, as thousands of tests for sulphur and BTU content in flammable vapors where the vapor is placed in a bomb along with oxygen under 400 or 500 lbs. pressure, have never produced a premature explosion. An explosion can he caused by oxygen coming in contact with lubricating oil in the oxygen lines.
(b) Matches in pockets of men involved: Chief Merrill indicated this to be a possible cause.
(c) Friction of rope, belt buckles, dome cap or nails in shoes: If Manila rope (known for its conductivity of electrical current) was used and allowed to contact the side of the dome opening, it could have been the cause either by friction or through electrical potential setup in the tank, due to possible failure of car grounding device, it being assumed rails upon which the car rested were bonded because of electric signal system.
(d) Static: Chief Merrill was of the opinion that static electricity was not the cause, because of the slow motion of rescue operations. However, consideration must be given to static electricity as the cause. The high temperature and low relative humidity were conducive to building up a considerable potential of static electricity. A factor not to be overlooked is whether either the victim or the rescuer was wearing rayon underwear. The writer was at one time quite conversant with static electricity in the middle west, and has noted its almost total absence on the Southern California Coast. For the past three months Southern California has been subjected to low humidity, and the writer has noticed that during this period, although he lives within 1 1/2 miles of the ocean, upon removing a rayon sport shirt after working in the garden, it gives on static freely in being pulled over his head. During the preparation of this article he has, through slow motion, been able to produce a static spark from this rayon garment. Therefore, based upon the existing climatic conditions at the scene, it is his belief that static electricity was anything but a remote possibility as the cause.
Undoubtedly the lean mixture in the upper section of the tank, particularly between the baffle plate and the top of the dome, was rapidly enriched from the heating of the victim’s clothes, and the resultant mixture came within the explosive range coincident with one of the causes above listed.
3. Preventive Measures: Because time was the essence in the rescue of the unconscious mechanic, it did not permit the use of steam to free the tank of flammable vapors. Further, steam could not have been used because of the beat causing burns. Likewise prevailing methods such as the use of carbon dioxide or the exhaust from a gasoline engine, produce inert gases which would intensify the asphyxia.
In the absence of any approved and immediate method of freeing a tank of flammable vapors, it is to be assumed that all means must be taken to prevent ignition of vapors contained within, to dilute these inflammable vapors or at least to drive them from the immediate sphere of action and at the same time to reduce the chance of ignition by killing any spark that might be created by friction. At every such incident there would be two situations: (1) The tank would be filled with a mixture that is too rich to explode, and after the explosive area at the entrance to the tank has been passed, there would be no chance of explosion, regardless of the sparks created: and (2) the tank would be filled with an explosive mixture and extreme caution must be observed that no sparks are created at any point. Therefore, in agreement with the suggestion of Lt. DeBoer it is the opinion of the writer that both external and internal application of water fog under high pressure, in combination with certain common sense preventive measures, is the answer to the problem. A similar rescue should be attempted as follows
- The rescuer should be shod with either rubber boots or rubber soled shoes, clad in clothing of non-rayon material with no external metallic objects, and any finger rings or wrist watch removed or covered with rubber gloves. Further, all equipment used should be of non-ferrous metal construction.
- Equip the rescuer with an oxygen mask. This oxygen breathing apparatus should not be used for more than 21 minutes after which it should be aired for not less than 6 hours before further use. The rescuer should be thoroughly familiar with its operation and warned against the removal of the mask while inside the tank because of the possible danger of the explosive mixture of oxy,gen with prevailing vapors.
- Before entry is made into the tank, the same should be provided with a substantial bond to ground, in order to drain off any existing static electricity.
- Before making entry into the tank, the rescuer should also free himself of all static by touching the ground before commencing operations.
- A water fog curtain should be applied directly over the opening to the dome to form a blanket to confine any explosive vapors that might contact external flame or spark, and to reduce the internal temperature of the tank while increasing its humidity.
- The rescuer should be lowered by use of a cotton rope, all possible care being exercised not to permit any part of his clothing or the rope to touch the sides of the opening.
Application of Water Fog
- A water fog applicator should be put into play directly over the rescuer and the victim. This water fog to reduce explosive hazard and afford protection in the following ways:
- Wash vapors from clothing and body of both the victim and the rescuer, reducing danger of rapid heating when passing through dome.
- Raise relative humidity in the tank, thereby reducing possibility of static electricity.
- Reduce internal tank temperature which, in turn, would retard the vaporization of any flammable liquid in the bottom of the tank.
- Displace the flammable vapors from the area where rescue work is being carried on—in effect, a water fog envelope to surround the rescuer and the victim, keeping vapors out and greatly reducing the chance of ignition by cooling any spark that might be created by friction.
- Smother oxygen from any possible source of ignition by diluting the area below the explosive range.
The exterior and interior water fog applications would tend to neutralize and hold constant both vapor and temperature in dome, thus permitting exit of both victim and rescuer, via rope hoist, without hazard even with high external temperature.
It is recognized that advocating the use of water fog will probably not be well received. Too many Fire Departments are not conversant with its general effectiveness. However, water fog has changed and will more and more continue to change the technique of fire control. In 1926 the American Petroleum Institute, at its Sixth Annual Meeting. was informed by Mr. G. O. Wilson of the Standard Oil Company of California. of his Company’s exhaustive tests in perfecting steam protection for oil tanks. The result of the tests indicated that to make a combustible mixture safe it should be steamed to a temperature of at least 170° which corresponds to a a saturation of about 40% steam by volume. It was pointed out—“It should perhaps be emphasized at this point, again, that the ‘fog’ which is commonly spoken of as steam, will not prevent ignition of a combustible mixture.” During the discussion following the paper Mr. Wilson was asked whether experiments were made using water in place of steam. Mr. Wilson answered— “We did a lot of work with that and were successful; but I have no data with me to tell you just how much water is needed; but water will extinguish vent fires. However, it is harder to get it uniformly distributed. Steam just naturally spreads itself all around when you turn it loose, but water tends to follow the line of the jet from which it is squirted out. We found steam was much more flexible and reliable than water. But I think a water smothering scheme could be worked out which would give reasonable protection under many conditions.”
Mr. Wilson’s statements were most prophetic, because since 1926 the use of water in the control of products of petroleum fires has been made positive by the development and adoption of water fog equipment. A local testing laboratory authority states that he does not believe water fog will displace enough of the flammable vapor to reduce it below the explosive range, because atomic laws prove that gases tend to maintain a uniform composition in a closed vessel, and it would be difficult to push away one gas with another.
Water Disseminated to Approximate Steam
Modern fog equipment with its required high pump pressures has made possible the dissemination of water in a condition closely approximating steam, and the extreme velocity with which it is disseminated would tend to displace or dilute in a sphere of placement the gas therein. Because of its cooling tendencies, water fog would undoubtedly retard the vaporization of any flammable liquid in the bottom of the tank and would thus prevent an increase of flammable vapor content. This same authority agrees that water fog extinguishes fire mainly through cooling action, it taking one pound of water to absorb 1000 BTU of heat. He then states in favor of water fog that it is quite possible that the cooling action of a fog curtain will keep the flammable vapors below the low limit of their incipient ignition temperature which is approximately 400° F. for petroleum vapors.
Until it has been proved that some other procedure is more effective, the writer confronted by a similar incident as that in Council Bluffs, would proceed with the use of water fog equipment as above outlined.
As previously stated, the writer submits this article to solicit interest and action and to the end that there will result a positive cure for a situation most malignant. While the Fire Service must lead, it is however also the responsibility of the manufacturers, producers and venders of materials producing explosive vapors, the public carriers transporting same, and research groups, to combine their facilities to produce the cure. In the process of gathering data, the writer contacted one of the largest public power companies in the west. The problem has intrigued this corporation, as in the production of power, a similar happening might take place, and it is preparing to conduct tests to neutralize the electric spark in a flammable atmosphere. The writer is gratified that at least his part in the discussion has provoked this first clinic.