Film-Tech Forum ARCHIVE: Projection Room Air Filtration

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Posted by Brian Guckian (Member # 1678) on 10-01-2005, 07:11 PM:

I'd be glad if anyone has any information on the optimum air filtration specs for today's projection rooms / booths.

I read somewhere a long time ago that 95% was desirable, but is this readily achievable?

Also, should air pressure be positive or negative in the room and to what degree?

Finally, what specs should apply to a dual booth where you've film and digital side by side?

Many thanks in advance.

Posted by Dave Macaulay (Member # 813) on 10-01-2005, 10:42 PM:

The less dust in the room, the less dust gets on the film, optics and electronics. Digital projectors have internal filters on the cooling air so reducing room dust would extend the operating life of those filters I suppose, plus keeping the optics cleaner.
The AMC buildings here use the booth as the return air duct for the auditorium a/c system, there are filters in the wall where auditorium air comes into the booth. The booths are actually fairly clean but they cover the prints when not in use and surfaces that don't get cleaned regularly do get pretty dusty.
With current booking schedules, prints don't stay long enough to get really dirty in a booth with decent filtration but anything with fan cooling will be a lot less trouble in a clean booth; amplifiers and rectifiers eventually overheat and fail as the internals and the fans themselves get coated with crud.
Just about any air handler filter should manage 95% of normal lint-type dust. The better filters (usually called HEPA although that term has become a meaningless marketing buzzword) are meant to catch smaller particles rather than a higher percentage of the larger ones (catching the small ones does consequentially get more of the big ones) so stuff like pollen is removed that flows through "normal" filters pretty freely.
Just as important as filtration is the cleaning routine. The floor and all horizontal surfaces need to be cleaned regularly using methods that trap the dust rather than just move it around; a vacuum with a good filter or wet cleaning is best. A crappy shop-vac that blows out most of the fine dust it sucks in is not a big help. Compressed air can be used to clean dust off small hard-to-clean stuff but most of the dust you blow off is going to settle back on everything in the area. Nothing else works as well a mop and a good vacuum.

Posted by John Pytlak (Member # 331) on 10-04-2005, 03:07 PM:

The projection room should be maintained under POSITIVE balance, so air with unfiltered airborne dirt is not drawn into the room.

Ideally, the system should have a high efficiency filtration system (e.g., HEPA) that removes almost all airborne particles less than a few micrometers in size. (Cheap spun fiberglass filters let many larger particles pass). Low cost HEPA filters are available that usually use a pleated porous paper filter media (e.g., 3M Filtrete, Purolator, Fram). Airflow should be properly directed so as not to stir up dirt.

When you clean, don't stir up dirt by dry brooming or using a regular vacuum cleaner that exhausts the air back into the room. Use a vacuum with a HEPA rated filter, or a central vacuum system that does not exhaust into the projection room. Or damp mop and wipe surfaces with a damp sponge. NEVER use a blower to move dirt around.

If you see noticeable dust buildup on clean surfaces within a matter of days, it is likely that your air filtration system could be improved. Likewise, it is very easy to see airborne dirt particles in the beam in front of the projection lens.

As noted, dirt gets on film, gets into sensitive electronic gear, clogs filters, and gets on optics and port glass. It is attracted to electrically charged surfaces like CRTs and high voltage power supplies. Fortunately, for the past six years, Kodak VISION Color Print Film now has a transparent conductive layer in the film that minimizes the buildup of dirt-attracting static.

Try to maintain film handling areas at 50 to 60% Relative Humidity. Temperature is not critical to film handling characteristics, but a goal of 20 to 25 Celsius is comfortable, and cool enough for most electronic gear.

Some good information on the Kodak website:

Kodak Film Handling Website

quote:
Room Cleanliness
Carefully look at the projection room and the inspection or storage area. Is it a clean, well lighted place? Any lack of cleanliness can be magnified thousands of times during projection of the film on the theater screen. Dust and dirt deposits that escape detection become very distracting at that level of magnification.

Ideally, you should handle motion picture film in a white room environment like that prevailing during its manufacture. But, in the real world conditions may be drastically different, resulting in dirt that can lead to abrasion. You should assess your own film handling situation by paying particular attention to the type and amount of ventilation, the materials used for floor surfaces, and possibilities for dust accumulation on the work benches and equipment. These are the main sources of dust and dirt that reach the film surfaces... (much more on the website).

[ 10-05-2005, 08:05 AM: Message edited by: John Pytlak ]

Posted by Brian Guckian (Member # 1678) on 10-06-2005, 07:43 PM:

Dave, John;

Many thanks for this invaluable information - much appreciated.

A lot of the problems I see are with the air supply rather than the cleaning routine so knowing the HVAC end helps enormously.