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Aviation History
1945
1945 - 0646.PDF
362 FLIGHT Relatively Safe Fire Risks Not so Qreat as Thought: Flash Point/ie Limiting Temperature By "BADRA" THE subject of so-carled safety fuel has again beenbrought before the public with the article publishedin Flight of February ist. Since it was mentioned recently also by Sir Roy Fedden, it may be said to be now a public issue. From the nature of his work, the interest of the author of the recent article on this subject is understandable. No one who has seen some of the results on the pick of our youth, consequent on petrol fires in aircraft not using a "safe fuel," can have any doubts as to the advisability of using a fuel which would avoid bun*—•* ups in military machines, particularly bombers, providing- it can match, or nearly match, in other requirements the fuel used to-day. Unfortunately, it would seem that at this stage of the war it is already too late to avoid the thousands of casualties which have resulted from not using it. Nevertheless, in spite of all the predictions that the reciprocating engine will be superseded within the next decade or so, a case is established for a thorough investi- gation into the merits of what to-day are called '' Safety Fuels" for use in military aircraft. • *~~ To use the casualties above-mentioned as an indi- cation of the need of such a fuel in civil aircraft cannot be substantiated. Indeed, one might go a stage further and say that in the true interest of aviation, such a delicate subject as this, where over emphasis of a remote possibility to air travellers can do so much harm, complete theoretical investigation and, if necessary, practical demonstration should be gone into before publicity is given to the subject. Something in a Name One of the strongest timbers in the planking of those advocating the use of "Safety Fuel" is undoubtedly the-*' clever choice of the word '' Safety'' as applied to the fuel in question. It is a matter of conjecture as to the difference this might have made in the diesel battle had anyone been astute enough to use the term " Safety Fuel" in connection with it. It cannot be refuted that, judged on the only standards applicable, diesel fuel has a much better right to be termed "Safety Fuel." What are the merits of Ibis so-called safety fuel over normal petrol in avoiding fire hazard? As the recent article pointed out the differ- ence? which may reflect in its favour are as follows: — FUEL TYPES c FUEL 100 Octane Conventional Aviation PetrolSafetv Fuel (of same anti- knock performance) ... Dissel Oil Initial and Final Boiling Point'C. • 40-180 150-220 190-360 - 30 + 45 -i- 80 Appro*. Spon- taneous Ignition Temp. °C. 450-500 450-500300 must be assumed to be spilt as a consequence of fracture of the tanps or fuel lines. Should a spark or flame b«— present, m. would appear to make no difference whether normaL^uel or so-called safety fuel is in use, since the ure of such spark or flame is well above the flash point of either. -It> can thus be seen that if by chance no spark or flame is present, the initial boiling point and spontaneous ignition temperature of the fuel may come into the picture should a lesser heat factor, such.as a hot exhaust pipe, be available. Since with the two fuels in question the figures for the latter are identical, the merit of the. former rests entirely on its higher initial boiling—-* point. To use words from the previous article to put this in plain language, "should fire occur ... its spread will be very much less rapid and intense, because the whole area of the crash will not be immediately permeated with highly inflammable vapour." It may perhaps be advisable to say soberly that the latter part of this quotation could *^ be a somewhat exuberant over-statement of fact! It may also be advisable to point out that 40 deg. C. (104 deg. F.) is a temperature not very familiar in our atmosphere at^, aircraft flying altitudes. What are the facts of the possibility of being killed by the crashing of a civil aircraft? In order to find out, it would be necessary to have such data covering the whole world. Unfortunately, the writer is not in possession of such figures, but they are available with sufficient search no doubt. They naturally fall into two main groups, which we may call public and private flying. Further- more, there can be no doubt that crashes in public flying are very much fewer in number than in private flying; in fact, it is well known to those interested in such data*— that accident figures in public air transport have been very low and tend to improve all the time. A large per- centage of all public air transport is flown' in the United States, and strict regulations prevail there guarding the safety of passengers. With the successful conclusion of agreements on the technical aspects of civil aviation recently at Chicago, which largely concern the safety aspects" of future flying, it is safe to assume that accident figures will continue to decrease. It is therefore of interest to note the following data covering this subject, as issued—•»» by the Civil Aeronautics Authority of the U.S.A.: — *r It will be seen that in the case of safety fuel both the initial boiling point and the flash point are considerably higher than normal fuel. For the uninitiated it should be explained that petroleum fuels are composed of a number of "fractions" boiling at different temperatures, and there is thus an initial boiling-point temperature when some of the fuel will distil off before the remainder. The flash point may be denned as the temperature at which an ignitable mixture of fuel/air vapour occurs at the surface of the fuel. The spontaneous ignition temperature is no... doubt self-explanatory, even though in technical phrase- ology it may be somewhat obtuse. It can be stated that, considering the aspects of fire risk involved, the flash point must be taken as the limiting temperature as regards fire hazard. This statement is made on the assumption that it is impossible in the event of a crash landing to say whether or not sparks will result in the vicinity of the fuel which Accidents Number of accidents Miles flown per accidentNumber of fatal accidents . Miles flown per fatal accidei Fatal accidents per 1,000,00 miles flown ...Pilot fatalities Miles flown per pilot fatality. Co-pilot fatalitiesCrew fatalities (other tha pilot or copilot) Passenger fatalities ... t 0 n Passenger miles flown per passenger fatality ... Passenger fatalities per100,000,000 passenger miles Crew and third party fatalities Total fatalitiesFatalities per 1,000,000 milts flowa 1940 42 2,590,4873 36,266,812 0.033 36,206,812 3 4 35 32,784,141 3.050 45 0.41 1941 33 4,030,9904 33,255,670 0.033 44,340,893 3 3 35 42,620,991 2.350 44 0 33 1942 31 3,551.7055 22,020,572 . • 0.055 22.020,572 5 6 . 55 20,814,248 3.730 71 0.64 1943 24 4,316,727,.'% 51,800,722 0.022 51,800,722 2 3 22 74,663,484 1.340 30 0.29 This with reduction from 359 to 194 aircraft. One other figure is needed to complete this picture, and that is the number of passengers flown. Over the four years shown, this figure was approximately 4,000,000 per year. It will thus be seen that in 1943 the chances of being killed whilst flying on airlines in the U.S.A. were around 180,000 to 1. Furthermore, and again quoting from 1943, a total of 24 accidents resulted in only two of them producing fatalities, the number of deaths as stated
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