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. 3 32 AIR COMMERCE BULLETIN With regard to the presence of gas in one of the meters it waa estimat that ju 1 bour the seepage'in the axial corridor would have amounted to one-forticth of 1 percent of the volume of the corridur; that even in the motionless condition of the ship, the corridor would have been well ventilated due to the chimney effect created by a wind of 6 knots blowing over the gas shafis; that the ventilation in the corridor would have prevented pockets of hydrogen from forming because the air current through the corridor was not lani- pated but was made up of whirls and eddies, However, if it could be shown that & rent occurred in a cell below the arial corridor, then it {a possible that some free hydrogen might have found its Wap into one of the meters, In regard to the ignition of exch mix- ture within a gas pressure, or fullness Ineter the following is quoted from a report of the Bureau of Standards, relating tu exhibit 74, one of the meters taken fro the ship: “It is evidently intended for measuring and giving a remote indication of smaii Zas pressures by electrical means. The pos pressure acts on a diaphragm in opposition to a helical spring. A plunger attached to the diaphragm carries a coil of wire which has a resistance of 100 ohms. Two rollers, connected in parallel, Make contact with th: sides of the coil. Two flexible connections run to the ends of the coil. The change in the relative resistances of the two pars of the cireuit between the contact rollers and the ends can cause suitable electrical indicating Instruments in the control cabin to indicate the position of the coil and diaphragm and hénee the Pressure, VAll electrical parts are enclosed in a cylindrical metal bor. The onty openings into this box are (1) the hole, 10 mm in diameter at the top through which the operating rod passes with a clearance of not over 0.05 mm and (2) the opening at the bottom which is completely filled by the 3-conductor cable (covered with metallic braid) which connects to the rest of the efreuit. The conical housing surrounding the meta? box is well ventilated. “The device seems to be excellently de- signed and constructed from the standpoint of safety, and there appears no way br which it could with €uy reasonable proba- bility have caused a fire, “An overheating of the device by short circuit seems imporsible. A short circuit external to the device would impose on it only the full voltage (24 volts} of the elr- cult and produce a rate of heat dissipation of less than 6 watts. A short circuit inside the device would not draw more then the 1 milliampere fixed by the externa] instru. ments. <A simultaneous short circuit both inside and out would blow a fuse. if one was present, before a dangerous tempera- ture was reached. Good practice requires Buch fuses on all circuits, and one was probably used. The normal operation of the device thould produce no sparks, Deterieration of the contact rollers or of the cofl, or a breaking of a wire inside the meta] box micht pro- duce a spark inside. Tt seems Impnasible that hydrogen should be present inside as {t could get there only by diffusion down the narrow clearance between the operat- ing rod and its guide tube, 50 min jong. A spark could be produced’ outaide the box on by the breaking of the 3-conductor cable. “This cable is strengthened br the metallic braid and runa in & protected Jocation along the structural member, It could not be determined whether or not the cable wae Gefinitely anchored to the Member, Lor whether the metullic braid was originally clamped to the metal bex, becuuse o (dumn- age Jn the fire.” 7 In the Ught of all the avaliable. evidence on this point we beijeve Wat the possiblity of igniting euch mixture by the means just described was very slight. RESONANCE EFFECT—IIIGH FNEQUENCY INDUCTANCE An attempt was made to discover if the ignition of guch mixture could baye been laid to apark emission due 10 resonance effect upon metal parts of the ship's in- terior caused by received radio waves of high frequency, here was on the field at Lakehurst, a localfger beam radio transinitter of low power, Maintained by an airline company, the on-course portion of which wis so situated as to puxa through the space oceu- pied by the ship at th: time it took fre. This transmitter was at that time about 1,500 feet from the ship. Its power output was 1 watta; its frequency 278 kilocycles, The wae field atrength authorized for this type of station is 1,500 microvolts per meter at 1 mile, which represents; fifteen ten-thousandths of 1 volt per meter meas- ured at 1 mile on the on-course portion of the range which. incidentally, is the aren of weakest radiated power. The Strength of this field 1s a0 low that it bas been com- pared to the power of a fly. So far as could determined, this iocalizer was the only transmitter that wos operating at Yake- burst at the time in question. It is not believed that other high-frequency stations, at Home distance from the fictd, could huve had inductive effect upon the airship. Witness Dieckmann, of the German Com- mission, stated that he and his colleagues bad been particularly interested in the pos- sibility of ignition ‘hrough high-frequency radio induction, especial after hearing the testimony of Witness Freund who Was engaged In paylng out a length of the stern cable at frame 47 when the accident took plice; that this port of the cable might have received impulars and thus electrical energy would have been conveyed inte the inside of the ship. However, it appenars that If such result was to oceur due tu in- ductive effect, a transmitter relatively close to the ehip and of consideravle power would have had to be operaijug at the time of the event. These conditions were not present. Resonance effect due to high-frequency generation within the ship was impossible because all the ship's transmitters had been shut down before the appearance of fire. Furthermore, the ship was carefully shielued against resonance effects generated from thin. Witness J. B. Whitehead put no stock in this possiliHty beeause of the fmall amount of energy that could have heen involved. Furthermore, once inside the ship in the form of oscillations in the structure ho damage could have been done, because the structure Itself was go large and so complex that there was no Posst- bitty of a small amount of energy setting the whole ship in oscillation and that oscil. Intion in separate parts, which perhaps contained high resistance, would be sbort- circuited by other parts of the ship, In view of the facts and the expert testimony given on this possihtlity. it May be gaid that {nm such inductance there was only the remotest chance that it was responsible for the elusive spark, ELECTROSTATICS Under this designation of electrient pns- sthilities there is now to be considered a zroup distinguishable from current. elec-