FIRE RISKS ON COACHES
Page 63
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IT would be a grave mistake to encourage any feelings of panic regarding the dangers of passible conflagrations in passenger vehicles. It must be remembered that petrol is undoubtedly an extremely dangerous commodity, and it is only its extensive use which has made us accustomed to handling it as if it had no great potentialities of destruction—in fact, the average man treats the risks inherent in it far too lightly and it really surprises us how few serious fires do occur,' considering the vast quantities employed.
In the case of large passenger vehicles, such as that which was involved recently in a serious tragedy, it is the rarity of such an occurrence that brings it so much to the attention of the public. To the best of our knowledge, the last accident of such a nature involving considerable loss of life took place seine years ago, and then was due chiefly to carelessness, and if the fire risks be considered in relation to the number ofpassenger-miles, it might be said, as regards the safety of the bus and coach, that the exception proves the rule. No method of locomotion, even walking, can be absolutely safe, From the information which we have on the subject it would appear that the vehicle to which we have made particular reference was built to conform with the present regulations and restrictions, including the situation and arrangement of the petrol tank and the provision of doors. We much regret, however, that, owing to the' tardiness of our legislators, there is not likely to be a Ministry of Transport inquiry. Such an inquiry would assist in finding any obscure cause for such an occurrence, although the vehicle was so badly damaged that only an important mechanical failurewould be likely to reveal itself.
Ways in Which Petiiil Fires Can Occur.
Let us analyse ways in which a fire can occur in a motor vehicle. Perhaps the most likely is a backfire in the carburetter, but this can usually be isolated fairly quickly and usually only affects the small quantity of petrol within the float chamber.
Practically all other possibilities of fire can occur only through the leakage of petrol. This may arise from flooding of the carburetter, loose unions, cracked or broken pipes or from the tank itself, the petrol, or the fumes therefrom, being fired by the exhaust, externally (as by the throwing down of a lighted match by a passer-by while the vehicle is stationary), or by, naked lights within the vehicle.
Serious leakage may also occur through fracture of the petrol tank, either under the effects of vibration or by being struck by the breaking loose of some revolving part, such as a propeller shaft.
Petrol tanks are now usually so arranged that if the fuel overflows when the tank is being filled, or is splashed out while the vehicle Is running, it falls directto the ground. It was a really serious danger when tanks were so arranged that they were encased by woodwork which could be soaked with fuel.
In the ease of a vehicle travelling at a fair speed it would be quite possible for a fire to be burning for some little time before it could be noticed by the driver or passengers, as the flames would be carried towards the rear by the draught.
The combustion of a comparatively small quantity of fuel close to the tank, as from a leaking joint, might quickly heat the tank'and cause internal pressure if the vent orifice were not large. Such pressure might burst the tank and so release the fuel in bulk. From the way in which the fire toot place in the coach in question, it would appear to us that flaming petrol must have been blown up through the floor; otherwise, it does not seem to us that the fire could have spread so rapidly, and we suggest that as a safeguard a plate of thin but strong steel could be arranged to form a bulkhead between the petrol tank and the body. This would deflect to the ground and sides the force of any possible explosion and prevent burning fuel or vapour from being injected into the vehicle.
The Dangers of a Loose Propeller Shaft.
• The flinging of a disconnutecl propeller shaft is a danger of so great an importance that it seems to us to necessitate the provision of stout emergency straps, quite apart from the question of the possibility of such a shaft damaging the petrol tank.
It is questionable whether the exhaust pipe or silencer can become sufficiently hot to ignite petrol; some part would have to be at a bright-red heat to do so, but we have often seen spurts of flame coming from a bad joint in such pipes. As a precautionary measure, however, they could be encased in asbestos, and the joints should be of some type, such as the ball and socket, which would avoid the stressing of the joint faces and prevent packing from being blown out.
Suggestions have been made that petrol tanks should be provided with a jacket of some form of fire-extinguishing fluid, such as carbon tetrachloride, but experiments carried out with tanks of this type on aircraft have not proved successful, the noninflammable vapour which acts as a blanket for the flames being too rapidly dissipated or not extended far enough to cover the whole area of the' fuel, anti if only a tiny amount be left burning this will serve to ignite the remainder.
The employment of metal bodies reduces fire risks from such a cause, but it would appear that the floor also might well be made in this material, although there are certain difficulties in the way of the latter. No ordinary fire-extting-uishing apparatus could be brought into action sufficiently rapidly to have any real effect in the ease of an explosion, although certainly extremely valuable for small or less violent outbreaks.
A Suggestion for a Fire Alarm.
It has been suggested that some form of indicator should be provided which would warn a driver Immediately a fire occurred in a part not visible to him. The idea has possibilities, as now devices can be made which will operate with a rise in temperature of only a few degrees, and the indicators could be mounted at various points all communicating with the one signal, which could take the form of an electric siren.
There is one point at which considerable heat is generated and to which we have not referred, that is the transmission brake, where this type is employed.
Since writing the foregoing remarks we have learnt more regarding the accident which prompted them, and it appears that this may have been clue to the breaking loose of the propeller shaft, a point to which, it will be noted, we have already referred. Further remarks are made in our leading article: we also draw attention elsewhere to a prize scheme, the results of which, we hope, will prove of distinct value in the reduction of passenger-travel risks!