The reclusive BFI master store is Edward Cullinan Architects’ intelligent response to the problem of archiving highly flammable film, writes Ruth Slavid. Photography by Edmund Sumner
There is something about the British Film Institute’s new Master Film Store that brings to mind the philosophical question first posed by Bishop Berkeley in the 18th century: ‘If a tree falls in the forest and nobody sees it, does it make a sound?’ In this case, though, it becomes: ‘If you design a building and nobody sees it, is it architecture?’
The film store, designed by Edward Cullinan Architects, is remarkably hidden. On the site of a series of former Cold War nuclear missile bunkers at Gaydon in Warwickshire, it is completely invisible from the road. And with only five people working there, plus the occasional driver delivering or collecting film, it will be seen by fewer people than almost any building in the country.
At the same time, it is very technically demanding. The store contains both nitrate film and the acetate ‘safety’ film that replaced it from 1951. Both deteriorate irrevocably, a process that can only be halted by low temperatures and low humidity. In addition, nitrate film is notoriously flammable and, once it starts burning, impossible to extinguish. The only solution is to allow it to burn itself out with access to plenty of oxygen – if the oxygen supply is restricted, toxic cyanide gases are emitted.
Constructing a master film store represents a change of direction by the BFI. Previously, the policy was to store film in ‘reasonable’ conditions and to copy it before it deteriorated too far. A process of digitisation had also begun. But when the institute received a £25 million grant for a new building, it was able to go ahead with its plans for top-quality storage. And when there were subsequent funding cuts, it put the digitisation on hold.
Film will be stored at -5°C, and at just 35 per cent relative humidity. At these low temperatures, the chance of nitrate film catching fire is minute. Elaborate precautions have still been taken, but the films are stored in 30 relatively large compartments, with more than 6,000 in each. The layout of the building could not be simpler. The main, technical, section has acetate film stored in the centre, and nitrate film along two edges. Technical equipment is at the rear, including dehumidification plant and back-up boilers. At the front is an administration building, with an acclimatisation room for film taken out of storage. This part of the building is separated thermally from the rest; refrigeration plant is on the roof.
The external walls of the nitrate stores comprise giant doors, weighing 1.2 tonnes each. They are held up by chains with fusible links, which means that if the temperature internally reaches 70°C, the doors, which are hinged at the bottom, will drop down and the flames will roar across the adjacent landscaped area. This area, which is planted with a wildflower mix and contains a swale to attenuate the rainfall that runs directly off the roof, is attractive but out of bounds to all but the man who cuts the lawn. If the fire alarm sounds, there will be a very brief time in which to evacuate the area before the flames shoot out. The doors are designed with two-hour hydrocarbon fire resistance, to prevent fire from one cell coming in to ignite film in a neighbouring cell.
The cells are constructed of high-quality, reinforced concrete panels, to achieve extremely high airtightness with only 0.3 air changes per hour (far better than Passivhaus standards of 1 ac/h). A sample cell was built on site to check that this level was achievable. Alongside the energy savings in the refrigerant and desiccant plant (see opposite) this allowed the building to reach BREEAM Excellent standard, an exemplary achievement for a building with such a high inherent energy requirement. Floors are suspended, to prevent the formation of permafrost.
The regularity of the cells, along with the flawless finish to the concrete, gives the building a pleasing rhythm in a manner that is surprisingly austere, even Brutalist, for a Cullinan building. The practice’s Robin Nicholson describes it as ‘the interesting point where engineering meets architecture’. The more obviously architectural element is the administration block, clad in profiled stainless steel, a seemingly extravagant choice justified by its low-maintenance requirement. The simple curved corners contrast with the severe right angles of the rest of the complex, and are offset by a steeply angled sedum roof (at the limit for viability) leading to another green roof on the main building.
While few may actually visit the film store, images will doubtless reach a larger audience and form part of the BFI’s marketing. This is not, then, quite such a ‘stealth’ building as it first appears, and is to be admired for its rigour and technical achievement.
The high levels of insulation mean that, once the cells reach their operational temperature, their refrigeration demand should be kept to a minimum. Services engineer Couch Perry & Wilkes specified the refrigeration equipment to be as efficient as possible, and visited a number of ice rinks as these are the nearest equivalent in terms of performance. Peter Broadbent, director at Couch Perry & Wilkes, said the building should not be compared to a cold store, where items are moving in and out all the time. Here, the environment is much more stable.
The main energy demand comes from the four desiccant wheels that dry the air down to 35 per cent relative humidity. These wheels, each about 1.5 metres in diameter, contain desiccants similar to those in the little packets found in many consumer goods. As they turn slowly, they remove the water from chilled air passed over them. The desiccant then has to be heated to 140°C to dry it out again, with fresh air passed through to remove the liquid.
The innovation in this building is that the engineer has introduced a heat recovery loop that preheats the incoming air, so reducing the required energy input. At the most demanding part of the cycle, in summer (because warm air contains more moisture), this pre-heat can raise the air temperature from a typical 20°C to about 80°C, before an electric heater raises it to 140°C. That is, it cuts the energy requirement by about half.
Couch Perry & Wilkes was obliged to use electric heating as there is no gas supply to the remote site, and biomass could not reach the required temperature. There is also heat recovery from the refrigeration chillers, used to supply heating to the administration areas. The back-up boilers are only for use in case of failure, or if external temperatures fall well below -5°C, in which case no refrigeration will be needed so there will be no waste heat.