British Kinematography (1952)

Mav, 1952 BROWN : PROBLEMS OF STORING FILM 155 sive and more convenient for working purposes to maintain steadiness at a higher temperature and in the National Film Library vaults this is what is done. The target temperature is 55° F. and we have found it possible to remain within a few degrees of this over a period of several years; and only on two or three occasions has the temperature gone outside this range, during a period of extraordinary weather. The vaults are arranged in blocks of twelve and are entirely enclosed within the building, the vaults being surrounded on all sides, and above, by a jacket of air. This air jacket serves in much the same way as the vacuum in a thermos flask; insulating the interior from changes in the tfmperature outside. In addition, to maintain the target temperature when the external temperature is lower, enclosed electric tubular heaters are installed in the corridor; and during the winter these keep the temperature within the vaults between 50° F. and 55° F. They are fitted with thermostatic controls which bring them in and out of action as required. During the summer when the outside temperature is higher than we desire, the interior remains cool. The mechanism by which this is achieved is: 1 The insulating properties of the jacket of air in the corridor. 2 The movement and escape of heated air above the vault ceiling. At the centre of the ridge of the pitched roof (Fig. 2(a) ) is a louvred ventilator and in each gable end, just above the level of the vault ceiling is a 9 inch square air brick. As the air in the roof space becomes warm it rises and escapes through the ventilator and cooler air enters through the air bricks to replace it. 3 To reduce the absorption of heat by the building, all the outside walls, and the roof, are painted white, in order to reflect as much as possible of the incident light and heat. In addition to recording instruments, readings are taken three times daily with a whirling hygrometer, to guide adjustment of thermostats and check the recording instruments. These vaults, I should point out, had to be built during wartime, within the limits of the framework of an existing building, and without any tests or experiment. They have always been regarded by us as temporary, but they meet the steady temperature requirements remarkably well, which is fortunate since, like a number of wartime innovations, there seems to be little early prospect of replacing them with an ideal establishment. The humidity within the building is not closely controlled by this construction, and varies over a range of about 30 per cent, but it is found that violent fluctuations do not occur, and due to the steady temperature, dewpoint conditions never occur. Fire Protection of Present Vaults. Let us now consider the protection afforded by these vaults from effects of any fire. In this, the greatest danger from a film fire in an enclosed space is that of explosion of an accumulation of gases, which might damage the vault and spread the fire. It is therefore essential to provide adequate means of escape for the products of combustion (Figs. 3 and 4) . The escape of gases is provided for by an opening 18 inches square in the ceiling of each vault, which leads through a brick built channel to the open air. The outside opening is closed by a metal flap, hinged at the bottom and held at the top by a dab of bitumen. In the event of a fire, heat would soften the bitumen permitting the flap to be fully opened by pressure of the gases. A further factor for which provision must be made is the escape of the vapours of the gradual spontaneous disintegration. A slow " breathing " of air through the vault is permitted by means of a small ventilator in the bottom of each vault door and an air brick in the side of the external part of the gas relief vent. Fire originating anywhere in one of these vaults would inevitably destroy the whole of the films in that vault.