◆ SpookStack

30 Habotage _ The possibility that the cause Is to be explained by premediated or wilful act bas recelved active attention. Sabotage hax H examined under two elassifications : the first—externa), ineludi the use of incendiary buliet, bigh- electric ray, and the dropping of an igniting composition upon the ship from an airplane: the second elasstiication—internal—including the plac- fog within the ship of a bomb or other in- fernal device. To date, there ie mo evidence to fodicate that sabotage produced the grim result. + Accidental Canses In a consideration of iden causes, two factors must be founfWogethet. There must be present (a) a combustible mix- ture of hydrogen and oxygen of the air; and (0) sufficient heat to iguite Buch mizx- . In ignition . are treated mixture and tts separately, PRESENCE OF COMBUSTIELE MIXTURE OF HYDROGEN AND alk Aceumalation Through Diffusion or Osmosia While it ia eonceded tbat the fabric of which the cells were made is slightly per- meable to the diffusion of the contained hydrogen, it is not our opinion that this characteristic of the cell walls, under the circumstances prevailing, would account for a combustible accumulation of gas and air within the ship; the normal rate of geep- age being. ag was indicated under descrip- tion of the cells, about 1 liter per square meter per 24 hours, FAILURE OF YALYE MECHANISM According to the testimony, only one valve failure had occurred on the abip. This happened when the ship was new; AR A consequence, ¢ertaln changes had been made fn the construction of the mechanism. In any event, the failure noted occurred to an automatic or pressure relief valve which would not have been functioning at the time of this accident. However, because the valves were mechanical devices, it was possible that there might have been a defect or fallure in them, but no testimony ap- pears to show that this possibility was a ikely one. DECREASED VENTILATION Another query regarding the presence of such mixture presented itself. Coula it have been due to the reduced scavenging of the gas by the ship's ventilation system during the last minutes of the craft's ex- istence when its speed eventually had been Teduced to a full atop, combined with the last valving operation, about & minutes be- fore the fire? This theory seems improbable because of what was said about the effici- ency of the ventilation system and because of the fact that the chimney effect created by, the 6-knot wind that was blowing at the ship’s elevation during the last 4 minutes prior to the fire should have evacuated Rractically ali of the gas from the shafts, he forward speed of the ship, reported to have been from 15 to 20 knots per bour, when the last valving operation was per- formed, should have been ample, it was stated, to have cleared the gas rapidly from the ship, A further argument made with AIR COMMERCE BULLETIN the analysis of the evidence the’ } regard to the scavenging of gas was that immediately after the laxt reported valving the abip's cugines were backed down ‘hard, and that tis deceleration should have tended te move the gas in the ship toward the bow and out through the forward gas shafts. In considering the production of auch mixture by the rupture of a cell or cells, there are at least several avenues to ex- plore, ENTRY OF PIECE OF PROPELLER Qne of these might be Iald to the fail- are of a propeller and the throwing of one of ite fragmenta through the adjacent part of the huli into a cell. To thia possibillty there was devoted apn extensive examina- tion by experts of our staff and those of other agencies. The condition of the pro- Peller of engine car no. 2 attracted our attention. Witness F. W. Caldwell, one of this country’s foremost Propeller ex- Perts, ware quite certain that the propeller of the after port engine did not break in flight but was shattered at the time the car struck the ground. He said tbat there was no indication of the separation of the theathing from the blades except as the re- sult of shattering on impact. Witness Deutsche, machinist in the after port en- fine car, indicated that the propeller of is car was still rotating when it atruck the ground; that he did not feel any un- usual vibration of the engine before the crash, FRACTURE OF HULL WIRE One other significant possibility must be discussed while tbe question of cell rupture is being examined, It was suggested that, while in flight, a tension wire might bave ripped a hole in a cell and thus permitted & quantity of fee to eseape, Coupled to this poasibility is the testimony of Witness R. H. Ward, digested briefly in the state- ment of facts, that he saw'a fluttering in the outer cover above the equator between frames 62 and 77 and believed that this fluttering was caused b fae escaping into the spate between the aalo hing cell and the outer cover. A shear wire fn one of the Panele at the place from which the gaa was escaping could have snapped while the ship was turning during the landing ma- heuver. Witness Eckener stated that such turns generate high stress in the after part of the ship, Erpectally in the center sec- tion close to the stab’ Neing fing which are braced by shear wires. é@ gas thus ac- cummlated between the cells and the outer cover ust have been a rich mixture. Such a mixture, enclosed in a space between the outer cover and the gas cells, would, if ignited, burn with relatively slow speed un- tll gas in greater volume waa released by the burning through of the cell walls. Wii- ness Rosendahi recalled that in the earty years of operation with naval afrcraft, shear wires had broken with varying effect, caus- ing no serious damage, however. MAJOR STRUCTURAL FAILURE Consideration has been given to the pos- Fibility that a major structural failure in the etern of the ship caused the hydrogen to be liberated by rupturing a cell and forcefully breaking an electric Jead or metal part, thus producing a spark. The fire broke out when the port trail rope, which held the ship to the ground, hbe- came taut. It was reported by some per- Bons that at, or about, the time ther ob- served the fre they heard a eracking sound from the stern of the ship, An ex-