Low Lying Fog Effect without using Dry Ice or Fog Machine

[Dalamar]

Originally Posted by gafftaper

Here's a safety notice on City Theatrical's site from the compressed gas association. I'm yet to find a documented death. But there are plenty of warnings like that from fairly reliable and official looking places.

Thankfully, there are no casualties reported from using CO2 in a theatrical environment, and, frankly, I would expect nothing less than professional caution every time CO2's involved.

That said, your problem is, in my opinion, easily solved.

a) MDG ICE FOG Q, a low lying fog generator, when prepared accordingly, can be operated with Liquid N2 instead of L-CO2.

b) Once its fog is warmed up, contrary to many other products out there, the fog vanishes completely, instead of rising up and mingling with your atmospheric effect: that's the whole point, isn't it?

c) I laughed at the "heavy socked actors" comment, but that's not entirely a bad idea.

d) a Full Dewar (Liquid refrigerated CO2 or N2) will provide enough fluid for ~70mins, if the tank is a 230 liters (~3 liters per min). You’ll also use 2.5 liters of MDG Low Fog fluid / hour. Use that to calculate your budget.

That said, I agree that using that much fog, for that long, is going to distract the audience to almost being annoying and defeat the purpose of the effect. But please, don’t take my word for it. I’m no director…

[JChenault]

Originally Posted by gafftaper

Here's a safety notice on City Theatrical's site from the compressed gas association. I'm yet to find a documented death. But there are plenty of warnings like that from fairly reliable and official looking places.

As an exercise ( because I have the mind of an engineer ) I wanted to try and quantify the danger of dry ice fog to humans. ( in this case the audience of the production).

I did some analysis to see just how much area we could make dangerous with ten pounds of dry ice making the absolutely worse assumptions we could. IE if I have a closed room that will keep all of the CO2 in it - how small would that room be to create a danger for any occupants of we injected ten pounds of CO2.

First of all - what volume of gas are we talking about? C02 has a molecular weight of 44 grams/mole. A pound 454 grams - so ten pounds would be 4540 grams or (5450/44) 126 moles ( rounding up). At standard pressure and temperature, a mole occupies 22.4 liters. - so our ten pounds of dry ice would yield about (126 * 22.4) 2823 liters. A liter is 61.024 cubic inches and there are 1728 cubic inches in a cubic foot - so our ten pounds of dry ice would produce about ((2823*61)/1728) 99.6 cubic feet of pure CO2. Let's round up to 100 feet to make the math easier.

The air we breath is 21 percent oxygen. From the Post that Gaff gave us we see that

12-15% (of 02) Breathing increases, especially in exertion. Pulse up. Impaired coordination, perception, and judgment.

So let's set our danger point at 15% O2. IE we may start seeing effects at 15% but they are probably not life threatening.

If we had a room of a fixed size filled with air - and we could add the CO2 such that it would force out the air, but all of the CO2 would stay in the room, we would have to replace 28.5 percent of the gas with CO2 to get the O2 to 15%.

So my 100 feet of CO2 would make inhabitable a room that is about 350 cubic feet.

If my room is 20 x 20 feet ( a smallish orchestra pit ) I would have the bottom 10.5 inches of the space at 15%. If the space were 10 x 20 feet - I would have the bottom 21 inches at 15%.

We can't make any hard analysis with more information ( how much dry ice - how big is the room, etc) but it is clear that I am going through a LOT of dry ice, and the space that it is moving into is really really small with no air flow, and no one lies down in the fog - there is little danger.




All of that said - I'm not sure it makes sense to spend the money, time, effort etc to do that much fog in a show - but I wanted to try and quantify the danger to the audience.

If anyone sees any holes in the analysis please holler.

[AdamBair]

in a dry ice fog machine, the dry ice is contained fully within the machine, so audience proximity is of no concern. But dry ice is still a no-go you could use liquid nitrogen, but that tends to be on an expensive fog system.

The lighting solution sounds like your best shot. The City Theatrical EFX can give you some nice moving effects, especially if you can pair it with a 70 or 90 degree lens on the source4.

[Dalamar]

Originally Posted by AdamBair

in a dry ice fog machine, the dry ice is contained fully within the machine, so audience proximity is of no concern. But dry ice is still a no-go you could use liquid nitrogen, but that tends to be on an expensive fog system.

The lighting solution sounds like your best shot. The City Theatrical EFX can give you some nice moving effects, especially if you can pair it with a 70 or 90 degree lens on the source4.

Yes, L-N2 is pricier than L-CO2: that's the main reason we use it.

So, my advice to you all, reading this: be mindful when using L-CO2, but use it anyway. It's the best solution to make a sustained, controlable, predictable cue safely.

[jwl868]

Originally Posted by JChenault

The air we breath is 21 percent oxygen. From the Post that Gaff gave us we see that So let's set our danger point at 15% O2. IE we may start seeing effects at 15% but they are probably not life threatening.

OSHA defines air as "oxygen deficient" when the oxygen level drops to 19.5% (see 40 CFR 1910.134). I agree with your calculation, but if the 19.5% threshold is used, the volume adversely affected by 10 lb of carbon dioxide increases to 1,500 cubic feet. Still, not much but now the 20' x 20' space is filled to 3.75 feet with an oxygen deficient atmosphere.

Joe

[icewolf08]

Originally Posted by AdamBair

in a dry ice fog machine, the dry ice is contained fully within the machine, so audience proximity is of no concern. But dry ice is still a no-go you could use liquid nitrogen, but that tends to be on an expensive fog system.

It is not a question of proximity to dry ice, but to the CO2 gas that is released (producing the fog) into the space as you evaporate the dry ice. The question is if it is safe to release that much CO2.

[AdamBair]

Originally Posted by icewolf08

It is not a question of proximity to dry ice, but to the CO2 gas that is released (producing the fog) into the space as you evaporate the dry ice. The question is if it is safe to release that much CO2.

Humans exhale about 2 lbs of CO2 a day *, so for every dozen people in the room, that's 1 pound per hour. If your theater HVAC moves enough air for the room to contain 240 people breathing for a hour, then it moves enough air for you to use 20 lbs pf CO2 per hour. Yes there will be people and fog generating at the same time, but this should give you some perspective on just how much dry ice it would take to present a hazard in a room the size of a theater.

* Carbon dioxide - Wikipedia, the free encyclopedia

[BillESC]

Dry ice does not evaporate, rather it sublimates. Goes directly from solid to gas by-passing the usual liquid state.

Although the above engineering is interesting, I don't believe a space, designed to hold public performances, could get a CO without an air exchange system in place.

[MaddMaxx]

Find your local light rental company. There are some great effects instuments available that can give you water, fog, etc..

[philhaney]

Originally Posted by amwindl

Any Ideas that are outside of the box...

But by definition, your show is in a box.....

Originally Posted by AdamBair

in a dry ice fog machine, the dry ice is contained fully within the machine, so audience proximity is of no concern.

Aye, but as has been pointed out, it's the CO2 the dry ice turns into that's the problem. Fog or haze "hangs around for a long time" in this space. CO2 is denser than O2 and will fill the room from the floor up (all that fancy engineering aside - nicely done by the way). It may be safe to use dry ice in this space for 70 minutes, but I wouldn't want to do it.

I would go with the "five minutes to set the mood and then turn it off" method or go with a nice lighting effect.

Even if you go with the "swamp gas" theory and just shoot a small puff up through various random spots on stage every 15 to 30 seconds (a different spot each time), at some point you will tick off your audience.....