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At any rate, in the space between stack No. 52 and the ceiling, flames were present at this phase. The remaining drums of film would thus be quickly heated; that is to say, those on the top layer of the stack.
Now nitrate film, when heated in closed vessels, instantly starts to decom- pose by the so-called "flameless decomposition", or "puffing". A large amount of gas, mostly inflammable, is evolved, and the reaction proceeds very quickly.
A high pressure is thus developed in the drums in a very short time, result-
This brings us to:
ing in the forcing up of their lids.
(b) Explosion.
This vapour forms an explosive mixture with air. It would not all burn immediately on evolution from the drums, owing to the limited supply of air in the space above stack 52, and some thus diffused around and downwards, where it would mix with fresh air.
When this mixture reached the flame, an explosion occurred in the general area of stacks 49-52. The wall was blown out, and drums and flaming celluloid film were blown backwards into the godown and out into the street, together with some of the rubber.
Such explosions are a usual feature of film and celluloid fires. They are not powerful or brisant, but relatively mild.
Another effect of this explosion was the bulging of the doors; those in Scavenging Lane powerfully, those in Whitty Street only slightly. The explosion would not be powerful enough to blow the bars of the small left-hand window into Scavenging Lane already referred to.
The other godown windows at this end were covered by stacks. It will be noted that the two Scavenging Lane windows near Stack 30 (Plan No. 1) shewed no heavy blasting. The reason for this is the probable presence, at the time, of Stack 30, a large pile of sulphate of ammonia, which covered these windows. The architect in Plan No. 1 has drawn these windows too far apart; in actual fact they both lie together behind Stack 30.
(c) Period of flaming of the film.
At this phase most of the contents of the godown marked in red on Plan No. 1 are afire from the flying celluloid film. All film drums are now lid-less and all the film is burning at a great rate, Nitrate film is highly oxygenated within the mole- cule, so that the rate of burning would not depend on the "draught", or air supply available.
These conditions give rise to a huge mass of flame which at first shot across the road, and then was carried back (presumably by the wind) against the front of the building. It roared up the narrow chimney-like stairs, and also cracked and burnt the French windows onto the verandahs of the flats above, then ran straight through the flats (which have no party walls in this direction), out of the back windows and so through into No. 2 Godown upper floors. The heat in the upper flats is attested to by the melting of glass objects inside the rooms (say 900°Fahr.) and here and there thin brass objects (say 1500°Fahr.) though not the electrical copper wires to any marked extent (therefore below 1900°Fahr.).
It should be emphasized that the high temperature in the upstairs flats above No. 5 Godown resulted, not from any "oven-like" effect from the flames beneath, but by the passage through them of the intensely hot mass of flame itself.
It seems likely that this flame, impinging on the windows of No. 2 Godown, broke them immediately (at any rate such as were not fitted with wired glass) and set alight to all floors of this latter godown almost simultaneously.
This may perhaps be clarified by the diagram on next page.