Low Lying Fog Effect without using Dry Ice or Fog Machine

[jwl868]

I had forgotten, but toxicity effects from carbon dioxide occur at lower concentrations compared to those that would cause oxygen deficient atmospheres:

NIOSH REL:
5,000 ppm TWA (0.5%)
30,000 ppm STEL (3%)
40,000 ppm IDLH (4%)

Current OSHA PEL:
5,000 ppm TWA (0.5%)

REL - NIOSH recommended exposure limit.
TWA - indicates a time-weighted average concentration for up to a 10-hour workday during a 40-hour workweek.
STEL - short-term exposure limit; unless noted otherwise, the STEL is a 15-minute TWA exposure that should not be exceeded at any time during a workday.
IDLH - Immediately Dangerous to Life and Health.
PEL - OSHA permissible exposure limit (This is enforceable).
ppm – parts per million (by volume).


Joe

[JChenault]

Originally Posted by jwl868

I had forgotten, but toxicity effects from carbon dioxide occur at lower concentrations compared to those that would cause oxygen deficient atmospheres:

NIOSH REL:
5,000 ppm TWA (0.5%)
30,000 ppm STEL (3%)
40,000 ppm IDLH (4%)

Current OSHA PEL:
5,000 ppm TWA (0.5%)

Joel

I was not aware of toxicity issues just due to the CO2 (as opposed to lack of oxygen) - Thanks for the correction.

So where does this get is on the scale of 'How dangerous could it be in the absolutely worse case we can imagine? ( Note that the scenario is intentionally designed to be the absolute worst case imaginable and is intended to be a mental exercise. )

Let's assume a target max if 1.032% of CO2 in the atmosphere. (CO2 is in the atmosphere at about .032 percent. NIOSH says shortness of breath occurs from 2% to 3%. The exposure limit for 8 hours is 0.5 percent - and for ten minutes is 3 percent. - 1.032% seems reasonable and makes the math easy).

From the earlier analysis we saw that 10 LB of dry ice yields about 100 cubic feet of gas. So we can make uninhabitable about 10,000 cubic feet of space assuming absolutely no ventilation. So our 20 x 20 orchestra pit ( 400 feet square) could be toxic up to 25 in depth. Humm.

Of course, this also means that the one pound block I put in the Halloween punch would make a 10 x 20 foot room toxic up to a height of 5 feet. Thank goodness for air flow.

It's also interesting that the safety warning from City Theatrical is ignoring the real issue.


Put putting aside all of that rationalization - you're absolutely right - it is more dangerous than I thought in a perfectly sealed environment. But it has nothing to do with lack of oxygen. Says to me that I need to make sure of air flow when doing dry ice in massive quantities. It's also interesting that the warning sighs are shortness of breath and deep breathing.

Now how much air flow would be needed to make a 20 x 20 room safe I leave as an exercise to the reader.

Thanks