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Radio-Canada Fights Archival Film Degradation with New HVAC Gas-Phase Air Filtration Strategy

Case Studies

Radio-Canada Fights Archival Film Degradation with New HVAC Gas-Phase Air Filtration Strategy

Engineers and archivists use carbon-based gas-phase air purification to preserve motion picture film and retard decomposition.

MONTREAL-- Older types of motion picture film have always faced slow degradation from acidic off-gassing that inevitably decomposes film into dust inside archival vaults, however a recent HVAC/R retrofit at the Canadian Broadcast Corporation (CBC)/Radio-Canada, Montreal, might offer a solution.

Since 2000, Radio-Canada--Canada's national broadcaster for French Services--has maintained proper temperature and relative humidity levels to retard ongoing film deterioration in archival vaults, but now the addition of gas-phase air purification appears to retard the degradation process.

Motion picture film archivists have traditionally used temperature and humidity control to retard natural degradation of nitrocellulose and cellulose acetate films, which have been used since the beginning of motion pictures until the 1980's when decomposition-proof, polyester-based film was introduced as an alternate for copying originals onto, according to Leo Enticknap, Ph.D., a lecturer and the Institute of Communications Studies' cinema director, University of Leeds, Leeds, U.K.

 Both the Society of Motion Picture and Sound Engineers (SMPTE), White Plains, NY, and the Image Permanence Institute (IPI), Rochester, NY, recommend temperature and humidity control.  The IPI even studied the "Vinegar Syndrome," whereas vinegar acids used integrally in older film style manufacturing methods actually attack the film from its inception and reside with it until the film eventually falls apart into dust. The study also found that temperature and humidity only controlled or retarded the decay.

 With Radio-Canada's older collections totalling more than 100,000 films and valued as priceless, archivists at CBC/Radio Canada began thinking outside the box to protect their archives.

Radio-Canada authorities andJean-Pierre Lachapelle, the company's preservation manager who retired in 2009 and is now a consultant with Archives V.I.P., Inc., Montreal, discovered the potential of gas-phase air filtration halting the degradation process all together by removing acid gases contingent with the film.

Lachapelle recalls reading about other archivists using gas-phase air purification, which has been used for decades to remove chlorides, oxides, sulphurs and a host of other chemical gasses that  potentially harm the industrial processes they're a part , the process equipment and employees 

Additionally, the gas-phase air purification manufacturer chosen for the project, Circul-Aire®, a Montreal-based subsidiary of indoor air quality manufacturer, Dectron Internationale, had also provided equipment to Hollywood Vaults, Hollywood, Calif., which Lachapelle visited.  Hollywood Vaults is a premier storage facility that houses archives from media companies, museums, educational institutions and private collections from around the world. Hollywood Vaults maintains a 45°F temperature and 25-percent relative humidity, but most importantly, is progressive in removing particulates with a series of conventional and high efficiency (HEPA) filters as well as gas contaminants with gas-phase air purification.

Unlike particulate fibre filters that come standard with all HVAC systems to meet indoor air quality (IAQ) standards, gas-phase air filtration is optional for customized HVAC equipment. Instead of particulates, gas-phase filtration removes gases by adsorbing and neutralizing them into alumina-based media.  One or more bed layers of the carbon media, depending on the expected amount and type of contaminants to absorb, are located in a facility's HVAC system or reside in a self-contained air handler within the room. In either case, room air is re-circulated through the carbon media to remove the intended contaminant.  In the case of CBC's archival vault, each side of the archival vault has a self-contained Circul-Aire Model APS-3000, two-stage air purification unit that draws acidic gases from the film container storage rack area, passes the gases through the carbon media for adsorption, and returns the purified air back into the room. Each individual film is encased in a vented canister and stored in 15-feet-high metal cabinets that are topless/bottomless to allow acidic gas build-ups to escape away from the film.

Each APS unit was custom-manufactured to deliver five stages of filtration: 1) a MERV-8 (minimum efficiency reporting value) pre-filter; 2) a bed of Media Mix-1100 active alumina impregnated with an eight-percent solution of potassium permanganate, the latter which prolongs media life and improves acid gas adsorption efficiency; 3) a duplicate bank of MM-1100 to provide a longer residence time and to assure adsorption during any potential spikes in acidic potency or when the second stage media begins losing absorbency; 4) a MERV-8 post-filter to capture residual gas phase media dust during media replacement periods; and a 5) a MERV-15 HEPA filter.

The ventilation design, performed by Circul-Aire, is critical to the process in order to eliminate ventilation dead spots where acidic gases remain too long in contact with film surfaces.  Air is completely re-circulated in the 3,000-square-foot room a minimum of 15 air changes/hr, versus three to four air changes/hr in more conventional spaces. Circul-Aire used a push-pull design where overhead ducts and down-flow diffusers by Titus, Richardson, Texas, push supply air down through the racks while a floor-level free return on each APS pulls the heavier-than-air acid gases along the floor.  Each system's upflow discharge supplies purified air through a ceiling-mounted duct truck line with branches networking over each film rack. The branches throw air down into each rack, thus the push-pull concept. The ductwork was custom fabricated by local contractors.

Circul-Aire also operates a state-of-the-art laboratory and its Tech-Chek™    program where clients such as the CBC periodically samples to determine the efficiency and remaining lifecycle of the media for replacement purposes.

The motion pictures of decades ago are important records of human history, culture and socio-economic factors.  Preserving them through the use of today's cutting-edge HVAC technology will undoubtedly be a benefit for future generations.

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