The Master Film Store, the world’s largest nitrate storage facility, will hold 450,000 canisters of film heritage. But as a nitrate fire is almost impossible to extinguish, the building had to incorporate some rather extraordinary design features. Ike Ijeh swaps his popcorn for sub-zero temperatures

There aren’t many buildings that combine Nasa technology and badger protection but Edward Cullinan’s Master Film Store for the British Film Institute is one of them. The £9m facility has been built to store the BFI’s priceless master film collection and is set to be fully operational from December. Hidden deep within the scenic Warwickshire countryside, it incorporates a futuristic, cutting-edge technology that belies its rustic location.

The building will store the 450,000 canisters of acetate and nitrate film that comprise the BFI’s celluloid collection. Between 1934 and the eighties, when polyester became the preferred material, most films were printed onto cellulose acetate, a fairly amenable chemical base that does not require onerous environmental storage conditions.

BFI

Cellulose nitrate however is an entirely different story. Used for the majority of films made between 1889 and the mid-twenties, it is self-combustible, has an incredibly low ignition temperature, can reach its maximum temperature in less than three minutes and, due to its high oxygen content, can continue burning even when submerged in water. As the scores of cinema-goers who tragically perished in the 1910s and twenties discovered to their peril, once ignited a nitrate fire is virtually impossible to extinguish.

Naturally, these attributes present a whole host of technical and environmental challenges with regard to storage, preservation and fire safety. Therefore the overriding principle throughout the design of the scheme has been containing rather than extinguishing any potential fire. In response, the project team has devised an innovative tranche of design solutions that satisfy this core aim. Chief among these is storing the nitrate in temperatures of -5°C, the ultimate mitigation against the ignition and spread of fire. The BFI Master Film Store consequently represents the world’s largest nitrate storage facility and the only one to deploy sub-zero temperatures.

The 3,000m2 building sits in a secluded clearing on a disused Ministry of Defence bunker that once stored nuclear warheads. The site was said to be untraceable during the Cold War, although classified maps discovered after the fall of the Soviet Union revealed that Russian cartographers thought otherwise. This remote, isolated location allays concerns about the potential fire risk posed to others by the presence of large quantities of nitrate. Ecological measures taken during construction included protection for the diverse local wildlife found on the site. This includes great crested newts, badgers and nesting birds.

Though simple and utilitarian, the single-storey building cuts a sleek, sculpted figure against its natural landscape. The building is essentially a highly articulated shed, but one elegantly wrapped in profiled, polished panels of stainless steel and slender, crisply honed concrete fins. As well as helping to construct a distinct architectural identity for the store, the use of steel and concrete is directly related to the building’s inherent fire prevention capabilities.

BFI

Four industrial chillers, four dehumidification units and 12 air-handling units deliver the optimum internal conditions of -5°C at 35% relative humidity required to store the film and prevent its deterioration. A pre-cast concrete frame also ensures the high thermal mass required to limit internal temperature fluctuations. In addition, a heat recovery system pre-heats the air required for the dehumidification process.

The building’s super-insulated external envelope incorporates a continuous vapour barrier that prevents moisture ingress and condensation and helps achieve an air-tightness that is 97% better than minimum building regulations standards. So the Film Store’s first defence against fire is the very fabric of its construction; it is essentially a super-insulated refrigerator tightly wrapped in concrete.

Internally, the Film Store consists of 30 identical cellular vaults for cellulose nitrate canisters and six vaults for cellulose acetate. The acetate cells are located in the centre of the building but as they pose a greater fire risk, the nitrate cells (above) are spread along the store’s perimeter. An access corridor divides the two on each side. Each nitrate cell stores 6,000 cans and measures about 7.7m x 3.5m with a volume of 98m2.

BFI

The overriding fire strategy throughout the interior has been rigorously enforced compartmentalisation. Extreme measures have been taken to ensure that should a fire break out in one cell it can be contained and not spread to canisters in neighbouring chambers. Although a worst-case scenario, nitrate’s chemical properties dictate that should a fire spread from one cell to another the results could be potentially catastrophic.

Accordingly, the cells are divided by twin pre-cast concrete walls and fitted with fire doors that can resist a hydrocarbon fire for two hours and fire dampeners. The doors’ design uses technology tested on oil rigs. Each cell door is fitted with an indicator nearby that flashes if the door is left open or if the lights within the cell are left on beyond a certain time, both scenarios that could potentially aid the spread of fire.

But the most ingenious measure is saved for the outer wall of the cell. This also forms part of the external wall of the building. This wall is actually a 3.5m x 3.2m detachable heat and pressure release panel weighing a mighty 1.2 tonnes and externally clad in steel. These steel panels are the same ones visible between the concrete fins on the side elevations of the building.

Each cell is fitted with a heat and pressure monitor connected to the panel via a fusible link. In the unlikely event of the temperature within the cell exceeding 75°C or if pressure in the room exceeds 2,500Pa, then the panel is automatically flung open by floor-fixed hinges to enable the fire to escape out of the building.

This enables oxygen to enter the room to facilitate what is known as a “clean burn”. If nitrate is not allowed to burn in this manner, toxic smoke laden with cyanide can form that can easily prove as deadly as the flames themselves. By expelling the fire horizontally out of the building, this also ensures that it does not spread to other cells within. The adjacent steel panels to neighbouring cells that remain in place would also enable heat radiation to spread along the outer skin of the building rather than permeating back into the other cells.

Once the panel has dropped, the force of a nitrate blaze within a cell could potentially send out a ferocious horizontal shaft of fire as far as 30m away from the side of the building. Consequently, a low inclined landscaped trench has been dug into each side of the Film Store to discourage access to this area. This extreme level of caution is by no means an overreaction. The average English summer normally emits tepid heat radiation of 0.67kW/m2. The area 100m away from nitrate fire can potentially suffer heat radiation levels of 25kW/m2

The release panels themselves are constructed to optimise their resistance to fire. The inner face is comprised of a 200mm skin of insulated Eurobond plaster. Beyond this is 50mm of thermal ceramics capable of withstanding temperatures of 1,400°C. This is the same material commonly used by Nasa on their space shuttle capsules. Next is a Superlux board before the outer face of stainless steel is applied.

The drop-down panels are a perfect metaphor for both the design and fire philosophy of the BFI Master Film Store. Architecturally they create elevations of almost classical rhythm and restraint, helping form simple but dignified bays of steel and concrete whose deep shadows and voids create a quiet, subtle drama.

Yet they are also central to a highly sophisticated fire prevention and management strategy that enables the building to more than satisfy its unique and onerous function. This is utilitarian architecture at its very best: compact, poised and nuanced but driven by engineering prowess and masterful technical innovation. The power of nitrate has quite literally met its match and the nation’s film heritage is in safe hands.

BFI

Project team

Client: British Film Institute
Architect: Edward Cullinan Architects
Main contractor: Gilbert-Ash NI
Project manager: Buro Four
Structural engineer: Curtis Consulting
Services engineer: Couch Perry & Wilkes
Fire engineer: Arup Fire
Quantity surveyor: W H Stephens
DM co-ordinator: Arcadis