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» Film-Tech Forum   » Operations   » Film Handlers' Forum   » Humidity in the booth

Author Topic: Humidity in the booth
James R. Hammonds, Jr
Jedi Master Film Handler

Posts: 931
From: Houston, TX, USA
Registered: Nov 2000

 - posted 02-14-2001 09:22 PM      Profile for James R. Hammonds, Jr   Email James R. Hammonds, Jr   Send New Private Message       Edit/Delete Post 
Ive seen in some posts dealing with static electricity that some suggestions were made to have humidifiers in the booth in order to help keep static away.

I was just wondering if I misread something because I was always told that humidity was bad for the booth and all of the theatres i worked at except for 1 had DEhumidifiers in them that we had to empty every morning.

If I havent misread anything and it is true that dehumidifiers are a bad idea and we should get rid of them, that would be great because I hate emptying those things.

Randy Stankey
Film God

Posts: 6441
From: Erie, Pennsylvania
Registered: Jun 99

 - posted 02-14-2001 09:42 PM      Profile for Randy Stankey   Email Randy Stankey   Send New Private Message       Edit/Delete Post 
Actually you might need to use BOTH humidifiers AND dehumidifiers in your booth...

You want the humidity in your booth to stay in the range of 50-60%. If the levels get too low you'll need to humidify. If the levels get too high then you'll need to DEhumidify.

Emptying out the DEhumidifiers? That's just as much a pain in the arse as filling the humidifiers... just in reverse. Do you have a way to hook a water hose to the thing and just run the condensate down the drain? Most dehumidifiers have this option.

There's an old Stephen Wright joke:
"I once got a humidifier and a dehumidifier... I put them together in the same room and let them fight it out."

Darryl Spicer
Film God

Posts: 3250
From: Lexington, KY, USA
Registered: Dec 2000

 - posted 02-14-2001 10:55 PM      Profile for Darryl Spicer     Send New Private Message       Edit/Delete Post 
Like Randy says try and maintain the booth humidity around 50/60 percent. Actualy 40/60 will work anything belowe 40 will cause extreem static anything above 60 and the film becomes tacky. I personaly do not believe in using humidifiers in the booth unless absolutly nessessary. to much humidity can cause electonic board failures and other problems. If your booth is properly air conditioned humidity levels should stay in the 50 percent range. Dehumidifiers are good if there is no way to get the humidity down and it will keep moisture out of the equipment. Hopefuly all of your projectors lamphouses are being vented out of the booth. If not this will kill your humidity levels. Try and maintain your booth tempreture around 65 degrees all year long. This will help keep the humidity within the percent range mentioned above.

Randy Stankey
Film God

Posts: 6441
From: Erie, Pennsylvania
Registered: Jun 99

 - posted 02-14-2001 11:09 PM      Profile for Randy Stankey   Email Randy Stankey   Send New Private Message       Edit/Delete Post 
Hey Darryl;

I will be comming up to Kentucky next week. Actually I'll be going to Louisville but I gotta' come through Lexington. I'm due in Tuesday.

Maybe we could check booth humidity levels, or something?

Darryl Spicer
Film God

Posts: 3250
From: Lexington, KY, USA
Registered: Dec 2000

 - posted 02-14-2001 11:26 PM      Profile for Darryl Spicer     Send New Private Message       Edit/Delete Post 
Hey Randy,

I work afternoons, Stop on buy.

John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

 - posted 02-15-2001 06:28 AM      Profile for John Pytlak   Author's Homepage   Email John Pytlak   Send New Private Message       Edit/Delete Post 
As Randy noted, Kodak recommends maintaining a relative humidity of 50-60 percent in film handling areas. At this humidity, the processed film will lie nearly flat, with just a bit of beneficial "positive curl".
Excessively dry conditions cause the gelatin emulsion to shrink, such that the film may curl severely. The lack of any moisture also makes the emulsion much less conductive, so static can become more of a problem.

At very high humidity, the gelatin emulsion becomes softer, such that it may scratch more easily or build up as hard deposits on the hot projector gate. Damp conditions may actually make the film sticky, and even CAUSE a static problem as the sticky film pulls apart during unwinding.

If the humidity is much higher than 60 percent, use a dehumidifier, which removes moisture from the air by condensing it on a refrigerated coil. Most air conditioning systems also remove moisture from the air. Excessive moisture is usually only a problem in the summer, during rainy or very humid weather (e.g., Houston, Miami, or New Orleans in the summer, or the Pacific Northwest almost anytime).

If the relative humidity is too low, use an evaporative humidifier to add moisture to the air. These humidifiers blow air through a wet foam pad or fiber filter material, and often can humidify over 10,000 cubic feet of space. Do NOT use an ultrasonic or misting vaporizer --- they actually spray water droplets into the air, leaving behind deposits of the salts and minerals that were in the water (not good for electronic components or film cleanliness). Steam vaporizers that actually boil the water usually don't have much capacity, and use alot of electricity.

Always monitor your humidity with an accurate digital humidity gauge or a sling psychometer. Radio Shack, Edmund Scientific, etc. sell these. The cheap analog dial gauges are often inaccurate and difficult to calibrate. Humidity can also be estimated by observing how a short piece of print film hangs --- it should be fairly flat, with just a bit of positive curl. Excessive positive curl indicates excessively dry conditions. Negative curl shows too much moisture. Again, the goal is to maintain between 50 and 60 percent RH.

You will find that the humidity will vary with the outside weather, and during the day. Large amounts of air are used by the lamphouses for cooling, and their heat dries out the booth. If possible, cooling air for the lamps should be supplied from an outside source, so the humidified air in the booth doesn't go up the vent. Venting the lamps into the projection room is a BAD idea --- the room will quickly become too hot and dry, and the ozone generated by xenon lamps is not good for your health. Most construction codes require venting the lamps to the outside.

Fortunately, the 50-60 percent humidity that is best for film, is also the most comfortable for people.

Here is some published information from Kodak:

John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
Web site:

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