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[l] The examination of the structural parts of tanks Nos. 7 and 6 disclosed no evidence of internal electrical discharges within said tanks (see par. 11.2.3,l);

[2] Tank No. 7 has two vent outlets (see par. lh.0);

[3] The two vents were not equipped With anti-flame screens (see par. 1h.0 and Annex XIV-l);

[h] No phy31cal evidence of llghtnlng strikes was found on the two vent outlets (see pars.ll.3.3 and ll.h.16),

a study was made of the p0551b111ty that the exp1031on might have been set off by ignition of the gasoline vapors issuing from the vent outlets, caused by discharges of static electricity (streamer corona). In fact, discharges of this typz wguld leave no visible traces on the outlets (see par. 11. .l.

This possibility assumes the coexistence of the follow1ng three conditions:

(a) That the gasoline vapors contained 1n tank No. 7 formed with the air a mixture that came Within the ignition limits;

(b) That the flammable vapors issuing from the vent outlets could be ignited by an electric discharge;

(c) That after the vapors had been ignited at the vent outlets, the flames could spread to tank No. 7 through the vent pipes.

For each of the three conditions mentioned above, the follow1ng observations are made.

(a‘) Taking into account what emerges indirectly from the 51x hypotheses set forth above, the fact that there was an exp1051on of the vapors contained in tank No. 7 would in itself indicate that the vapors were capable of being ignited. This may be ascribed to

[1] An aging process of the gasoline realdue contained in tank No. 7 (see par. 1h.l and Annex XIV-l), or

[2] A penetration of air 1n tank No. 7 through one of the two vent outlets, the conditions for such a c1rcumstanca having, 1n some way, been produced by the akistence of the two outlets (see par. 1h.0), or

[3] By the possible loss, in flight, of the P.N. 750h38-13 cap, taken p0551bly as a circumstance in conjunction with the two preceding ones (see pal". Ill-140203, moi-1113513 C):