Cellulose Nitrate Film Preservation: Putting the Smoldering Debate on Ice

Tuesday, May 29, 2012

Libraries and archives are charged with saving and maintaining what the rest of society might consider outdated and irrelevant technologies. Old carbon copies, dittos, video tapes, audio cassettes, Polaroid photographs, and documents on parchment are a few of the varied historical materials at Hagley. We strive to preserve these items, but by nature no object can last forever, and most materials undergo some type of decay or chemical change overtime. Sometimes, the objects of our heritage are not only decaying before our eyes; the products of their deterioration may produce other hazards. Cellulose nitrate film is one material that is often demonized due to its combustible chemical composition.

In photographic archives, active preservation efforts focus on the film based materials. Cellulose acetate and cellulose nitrate are the two types of unstable plastics used as the support for photographic film. It is extremely important to be able to identify the difference between the two, because cellulose nitrate is highly flammable. A posting on an archives list led me to consider why the preservation community is still so very spooked by this material. The current smoldering debate was about the Berlin National Archives and whether they should keep or destroy nitrate films once a duplicate has been created. Early tragic incidents involving cellulose nitrate film, as well as the costs associated with maintaining a film collection are the most likely reasons that an archive would dispose of original historical materials.

In the early twentieth century, cellulose nitrate film was responsible for deadly fires in theatres and at the Cleveland Clinic where over 120 people died. Many in the press and public like to dramatize the dangers of cellulose nitrate, and some have even stated that it is not a matter of “if, but when, it will burst into flames”. Fortunately, the dangers of nitrate film are manageable. What is needed are cool temperatures and low humidity to halt the chemical reactions that drive its deterioration. Keeping the film frozen is the ideal situation. Cool temperatures are also important for fire prevention, since deteriorated nitrate film produces heat on decomposition and can self ignite if ambient temperatures are over 100◦F. Fire prevention strategies and appropriate venting and fire suppression systems are obviously important when storing cellulose nitrate. The most recent nitrate film storage archives have been designed with multiple vault-like compartments that can contain a fire and keep losses at a minimum.

These are all safety precautions that were lacking in the instances of the deadly fires. In fact, the Cleveland Clinic fire was caused by three tons of X-ray films stored in a basement room near steam pipes, without sprinklers, and with ducts that vented the acrid smoke throughout the hospital. The smoke alone was said to have caused many deaths, through inhalation of toxic nitrogen peroxide.

The amazing thing about cellulose nitrate film is that much of it still is in quite good condition, even after nearly 100 years. It is notable that most of the badly deteriorated film found in archives these days is the cellulose acetate variety. This is probably because of previous campaigns to quickly duplicate and destroy nitrate films. Most people who still remember photographic film will likely have cellulose acetate film at home. Cellulose acetate (called safety film, because it is not flammable) had supplanted the use of cellulose nitrate by 1950. Unless like me, you have inherited some old cellulose nitrate from two or three (or four) generations back. If you do have cellulose nitrate film at home, most family collections will not be of such a volume as to create significant fire risk, since large quantities stored together are most likely to generate heat on decomposition.

Like any other important possession, negatives should be stored in away from heat. They should be stored in paperboard and paper enclosures, instead of plastic. Most importantly, keep them out of the attic! If you find deteriorated negatives that have yellowed, are sticky, and smell like camphor or have a sickening odor they should be disposed of properly. As was noted earlier, acetate film is also unstable and smells like vinegar when it degrades, but it is not flammable. Cellulose nitrate film CANNOT be disposed of in standard trash. Because of its flammability, it must be handled and disposed of as hazardous waste, and with specific precautions in place. For more advice on disposal and preservation of cellulose nitrate film refer to the National Park Service Museum Handbook, Appendix M: Management of Cellulose Nitrate and Cellulose Ester Film.

Laura Wahl is the library conservator at Hagley Museum and Library.