Film-Tech Forum ARCHIVE: DLP projectors and fog machines

This is topic DLP projectors and fog machines in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Antti Nayha (Member # 4980) on 04-12-2019, 07:26 AM:

Something that a couple of customers have asked me: Is it safe to use a fog machine for a short time in the same space with a D-Cinema projector? I'm talking about a boothless, non-hushboxed installation, where the projector would just be sitting there in the back of a room in a pop-up cinema venue – or even a club space.

I've always presumed that this could pose a hazard for their expensive equipment and potentially void their warranty. Then again, there are lots of club spaces and event venues around the world with fog machines running almost 24/7, and big regular (non-DCI) DLP projectors installed all over the walls…

I haven't asked for an official word from manufacturers yet, but I thought I'd ask you film-techers first – just to see if anyone happens to have either more information or first-hand experience about this?

Posted by Marcel Birgelen (Member # 6801) on 04-12-2019, 08:54 AM:

The answer is: It's complicated...

First off all, what kind of fog are we talking about? The oily, propylene glycol based kind of fog? Or dry ice?

The big venue machines from both Christie and Barco often don't really differ much in their design from their DCI counterparts, yet, they're often deployed in, let's say, more aggressive environments, complete with fireworks, smoke effects, etc.

Now, your average big venue projector will usually not have the same lifetime as your average DCI machine. The constant transport and handling of the equipment obviously is a big factor in this.

In the end, if this is a one-time thing and you don't expose your projector to the brunt of the impact of the smoke effect, I won't really expect any averse effects on the machine. Yet, if you do this every day, then expect some side effects, especially if you use the heated smoke liquid kind of effects, as they almost do contain mineral oil.

Posted by Paul Finn (Member # 10726) on 04-12-2019, 08:58 AM:

The fog particles condense and deposit on all exposed surfaces. Like the oil mist in the air from pop corn machines. Some 'effect' fog is water based and some is oil based with only the human hazard(s) evaluated for exposure when using. I believe fog can be detrimental to any digital cinema projector innards in short order. Christie does make special two stage "fog" filters for some of their large non-DCP projectors. The filters have a twenty hour life and have to be changed after every use.

Posted by Carsten Kurz (Member # 5396) on 04-12-2019, 06:56 PM:

Well, I would say it's safe if it is a one-time event and if the fogging is used in a 'normal' scheme - e.g. the fog machine not immediately close to the projector.
The effect is probably similar to the situation with a popper in the same building. It's not good, but, for a few hours, nothing serious.
Plus, a typical auditorium is not a clean-room even under normal conditions, so, boothless always challenges the projector a bit. I also think the room ventilation/HAVC will do away with some of the fog residuals before it reaches the projector.

- Carsten

Posted by Randy Stankey (Member # 64) on 04-12-2019, 09:23 PM:

While propylene glycol fog, by itself, is relatively inert it will coat any surface it comes into contact with in a thin layer of viscous liquid. That layer of liquid will collect dust and dirt.

Your optics will get dirty in short order and any internal parts of the machine that aren't protected by a good filter will become fouled.

I would say that, for short periods of time, you won't see much harm but, over time, your projector will get dirty.

As others say, if this is a one-time thing, you shouldn't have problems but, if this is a continual thing or if your projector is exposed to high concentrations of fog, you will have to spend a lot of time cleaning your machine, inside and out.

Posted by Jarod Reddig (Member # 6363) on 04-12-2019, 11:07 PM:

About 20 years ago a friend of mine had won a settlement and to celebrate he threw a giant party at his ranch house. He rented a bunch of party lights and stereo equipment including 3-4 fog machines. We set them up inside his house where he wanted them and they used the oil based stuff. After the party was over the next day the fog machines had left a terrible residue on everything. It just smeared around too when we tried to wipe it. I would hate to have a projector in an environment at all like that if the fog machines used the oil based stuff.

Posted by Randy Stankey (Member # 64) on 04-12-2019, 11:23 PM:

In all my years working on a stage, I never used oil based fog.

As you say, it coats everything in oil but, more importantly, glycol based fog is far less likely to cause respiratory problems in sensitive individuals.

Propylene glycol is the base used in e-cigarettes and as the carrier agent in asthma inhalers. If you can inhale the stuff, directly out of a vaporizer or atomizer without causing problems, it's reasonable to assume that it would be safe for 99% of your average theatergoer.

It's always been glycol or dry ice any place where I worked.
If you want a really neat effect, put some glycol fog through a dry ice chiller and you'll get a cool looking ground-hugging fog!

If you're using dry ice fog, I wouldn't expect there to be any detrimental effects on a projector unless you blow the stuff directly onto the machine.

Posted by Marcel Birgelen (Member # 6801) on 04-13-2019, 01:47 AM:

Dry ice usually is the most harmless type of fog effect, since it's just frozen CO2. The worst that will happen is that it will cause some condensation on the surface of the machine.

Off course, dry ice is usually also the most expensive smoke effect to use and since you probably don't have the cryogenic storage environment for it, you need to order the dry ice in advance, every time the effect is needed.

Dry ice also creates a very specific smoke effect, as it tends to stick to the ground.

It's also an effective way to cool down a hot room if you have plenty of the stuff. [Wink]

Posted by Mark Gulbrandsen (Member # 72) on 04-13-2019, 11:13 AM:

Years ago, 1997/1998, I used to repair fog machines. There are two types of machines, one uses oil based fog solution and the other is water/sugar based. The oil based stuff works better and stays in the air longer. But having seen what the both types can do to the insides of a fog machine I will only say keep it away from your DLP equipment, unless your DLP equipment is situated so it intakes air from a seperate clean air source.

Mark

Posted by Jarod Reddig (Member # 6363) on 04-13-2019, 09:59 PM:

Oh cool Randy and Marcel. Thanks. So thats how they get the ground fog effect to work. Always wondered . I pondered how that worked when I would see it done but then forget later to research it.

Posted by Randy Stankey (Member # 64) on 04-13-2019, 10:27 PM:

Dry ice fog (carbon dioxide) is cold and heavier than air but it dissipates fairly quickly. Propylene glycol doesn't dissipate as fast but it isn't as dense as CO2 so it doesn't hug the ground.

If you make a dry ice fogger out of a 55 gal. drum, a blower, an old heating element out of a water heater and some dryer hose and connect the output into a Coleman style cooler filled with dry ice (cut holes in the sides) then connect another hose to the output of that and feed it out onto the stage, you'll have a thick, glycol fog, that hugs the ground similar to CO2 but doesn't dissipate as fast.

Two of those units can fill a 40' x 80' performing area in a minute or two.

Fill up the stage with the main curtain down, a few minutes before the scene opens and, when the curtain goes out, a fog will roll off the front of the stage and the first few rows of the audience will be knee deep in fog in about 30 seconds. [Cool]

Posted by Jarod Reddig (Member # 6363) on 04-14-2019, 12:04 AM:

Be fun to play with Randy!

Posted by Randy Stankey (Member # 64) on 04-14-2019, 12:34 AM:

It's as much fun to invent and build stuff like that as it is to play with it after it's built. [Big Grin]

Posted by Steve Kraus (Member # 476) on 04-14-2019, 10:43 AM:

If someone does an event at my screening room, they can set up their own refreshments or have a caterer come in. I don't get involved (except to partake if invited or they're not looking LOL); we don't have a "preferred provider." This has never come up and probably will not but if I ever saw someone setting up their own popcorn machine, big or small, I would tell them either they cannot or maybe set it up far away. Definitely don't want oily air on the projector optics.

Posted by Jesper Meng (Member # 7575) on 05-13-2019, 03:12 PM:

I have used one of my Barco 32B's several times where we had a hazer running.
Last year when i had to repair a temperature sensor, the light engine was at the factory.
They told me that my prism needed cleaning, some sort of residue.
I am pretty sure that it is the hazer, a Swefog Ultimate cracker that uses mineral oil.
The Swefog has an extreme low consumption, i have used under 10 liter for the lasted years, so i thought i was safe.