Cellulose nitrate film, more familiarly known as nitrocellulose, became popular in the late 1880's because its physical properties made it ideal for photography. At first, cellulose nitrate film was used mostly for still photography, but it was also used for x-ray film and motion picture film into the early 1950's. Museums and photographic archives are often faced with the problem of safety in the handling and storage of nitrate film.
In 1988, the National Fire Protection Association (NFPA), published NFPA 40, the Standard for Storage and Handling of Cellulose Nitrate Motion Picture Film. This code does not cover x-ray film. The NFPA has produced documents for nitrocellulose film since adoption of the first standard in 1919. Because manufacture of nitrate film was stopped in 1951, it was debated whether to suspend regulation of such film in 1979. It was decided that because of the large quantities of cellulose film stored in archival collections, the standard was still relevant. NFPA 40 also addresses projection room requirements for the handling of nitrate film, and also specifies construction and arrangement requirements for buildings. Flammability
Cellulose nitrate film is highly unstable and presents a very serious fire risk since it burns quickly with an intense flame. The rate of combustion for cellulose nitrate film is about 15 times that of wood. In the early days of the motion picture industry, movie houses and even film studios had devastating fires with many fatalities. Dry cellulose nitrate can explode when subjected to heat or shock. While decomposing motion picture film has been known to self-combust, still-camera negatives have not. Cellulose nitrate contains chemically combined oxygen in sufficient amounts to allow burning and decomposition without the presence of air.
Toxic and flammable gases formed during burning or decomposition may be produced so rapidly that dangerous pressures may occur in building structures. The burning of cellulose nitrate film releases highly toxic gases, including nitrogen oxides and carbon monoxide. In one fire, these toxic gases were responsible for the deaths of 125 people not directly exposed to the fire. Since 1951, motion picture film has been produced with a "safety" base of cellulose acetate or other slow burning esters or polyesters. The fire hazards of these are similar to those of thick paper, and when these films burn, there is no release of toxic nitrogen oxides. Because lower levels of heat will result in damage to "safety" film rather than to paper records, special protection is needed to prevent fire damage.
Cellulose nitrate film decomposes over time to release toxic nitrogen oxides. These toxic gases are skin, eye, and respiratory irritants, and have poor odor warning properties. Chronic exposure to the decomposition products of nitrate film, especially nitrogen dioxide, can lead to headaches, blurred vision, loss of appetite, emphysema, and other systemic damage. In the presence of water, these gases can form corrosive acid gases that can lead to damage of other photographs and metal corrosion.
The decomposition and flammability of cellulose nitrate film makes the immediate identification and proper disposal of this film necessary, while at the same time preserving the materials stored with nitrate film. Although some still photographic negatives have the word "nitrate" printed along one edge, many nitrocellulose film negatives are not marked. Nitrate film should be stored in accordance with NFPA 40 - Standard for the Storage and Handling of Cellulose Nitrate Motion Picture Film. Below is a summary of the NFPA's recommendations.
The NFPA gives specific requirements on the type of construction required for buildings and laboratories that handle and store nitrate film. Buildings must be of Type I construction (see NFPA 220, Standard on types of Building Construction). All rooms in which nitrate film is stored or handled shall be separated from each other by partitions that are continuous and securely anchored, and openings through these must be fire doors that meet the standards of NFPA 80. There must be two exits and adequate aisle space. Projection rooms, rewind rooms, and rooms in which the stored amount of nitrate film is less than 20 rolls are exempt from specific explosion venting requirements. The NFPA requires at least 35 square feet of floor area for each worker in inspection rooms, and no more than 15 people may work in a room where nitrate film is handled. Tables, racks, electrical equipment, heating equipment, and duct systems should comply with the specifications detailed in the standard.
Except for motion picture projection room of booths or rewind rooms, every room in which more than 50 pounds of nitrate film is handled should be protected by an approved automatic sprinkler system. Other areas, but not film cabinets or vaults, may use either an automatic sprinkler system or a deluge system that has fixed nozzles or open sprinklers (see also the regulations on the water supplies for sprinklers). Every room where nitrate film is used or stored should have portable fire extinguishers with water or water solutions.
Nitrate Film Storage
The NFPA standard specifies the allowed amounts of nitrate film that can be stored. 25 lb (5 standard rolls) to 750 lb (150 standard rolls) should be stored in approved cabinets or vaults. Amounts over 750 lb must be stored in vaults. Archival film should be stored in archival cabinets or archival vaults. Film cabinets, film vaults, archival vaults, and archival cabinets are restricted in terms of ventilation, construction, materials, sprinklers, and dimension in accordance with the standard.
The handling of nitrate film also requires particular care. The NFPA specifies that all nitrate film must be kept in closed containers unless being worked on or examined. These containers can be individual metal cans for each roll. Those containers approved by the U.S. Department of Transportation (DOT) for shipment are particularly suitable. Film should not be stored so that sprinkler discharge would be hindered, i.e. under benches or tables.
Scrap film must be kept separate from paper waste, scrapped safety film, and other rubbish. Nitrate film to be discarded should be collected daily from the work area, and removed to an unused room. Safe storage of the scrap film includes underwater storage in steel drums or tightly closing metal containers.
A storage vault can also be used. Scrap nitrate film should be disposed of frequently. Nitrate film should never be baled or burned. The DOT regulates transportation of nitrate film.
Projection Rooms and Special Processes
Motion picture projection rooms are especially regulated, with specifications for fire resistance, enclosures, exits, openings, all shelves, furniture and fixtures, ventilation, and lighting. Processes like splicing, cleaning, repairing, cataloging, and marking may be done in common work areas, but not in rooms where other operations are performed. The authority having jurisdiction shall be consulted to determine the necessary protection against the hazards involved in special processes. These are the types of activities that archivists, conservators, and museum personnel are often involved in. Listed below are some general health and safety guidelines.
1. All cellulose nitrate motion picture film and decomposing film should be copied disposed of immediately according to the local fire code and NFPA regulation. NEVER incinerate nitrocellulose film. A sign of decomposition is when the emulsion becomes soft and tacky. 2. Only negatives in good condition should be kept. Nitrate film in good condition can be stored in acid-free, buffered paper. Duplicate cellulose nitrate negatives and properly dispose of the original negatives according to the local fire code, NFPA, and the DOT. Duplication of nitrate film can be done in two ways. The first option is to strip the emulsion from the base and transfer it to a new and stable support. This method is only useful for negatives whose decomposition has not affected the gelatin emulsion layer. The second option is to copy the negative onto duplicating film and provide negatives from which prints can be made. In both cases, be sure to inspect the duplicate carefully and approve its quality before the original film is discarded. 3. Store cellulose nitrate film in a cold room where temperature and relative humidity can be carefully controlled. A suggested relative humidity is 35%. Ventilation must conform to NFPA regulations. 4. When handling nitrocellulose film, wear neoprene or buna-N gloves. If there are signs of decomposition, wear goggles as well and provide local exhaust ventilation consistent with NFPA regulation. The hazardous decomposition by-products of nitrate film have poor odor warning thresholds. 5. Because all the hazards associated with nitrocellulose film increase with age, it is imperative to address safe storage and conservation before deterioration prevents conservation.