CO2 Jets the low down please
Posted 29 July 2012 - 08:00 AM
Posted 29 July 2012 - 08:56 AM
As an exercise it's quite easy to work out how much you raise the CO2 level in a space when using them.
Usual level of CO2 in air
Maximum amount of CO2 used in a show
Danger levels for CO2 in air
Volume of space
ie 45kg of CO2 (= large cylinder) will raise the level to 1% (=some people drowsy) in a space of approx 4,000 cubic m.
4,000m3 is a room 4m high by 30m wide by 30m long (=smallish event space)
Another way of looking at it is to compare the additional CO2 to that produced by people breathing...
I've seen a figure of 5g/person/minute of exhaled CO2.
So, 45kg of additional CO2 is the same as that produced by 150 people in one hour. Is that a problem?
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Posted 29 July 2012 - 10:20 AM
I suppose as has been alluded to above it depends on the speed of saturation of CO2 into a space. But, when you consider the orchestra are creating CO2 much more rapidly than a person sitting and not doing much in the way of activity then there does not seem to be that much of a worry. Plus there may be a constant flow of CO2 into the orchestra pit(s) from auditoria the world over and nobody has remarked thus before now. Some older theatres may not have had air handling facilities in the days of yore anyway.
It might be worth noting that when giving mouth to mouth/nose resuscitation the recipient is receiving a higher dose of CO2 anyway cf the normal amount by virtue of said air being "secondhand" so to speak.
That said I gather that the CO2 in the body is necessary to invoke the breathing in part of the respiratory cycle.
If it was that dangerous I am sure "we" would have noticed by now and all spaces below ground in a theatre would be vented, with all access being denied if the vent fans packed in.
Posted 29 July 2012 - 11:02 AM
I've seen podium dancers with smaller CO2 cylinders in a Scuba type backpack, with CO2 Lances like a pressure washer jet, Any wisdom to share?
Posted 30 July 2012 - 11:27 AM
Posted 30 July 2012 - 04:33 PM
Why, am I so cautious, you ask? Unconsciousness is almost immediate and the best studies have been those around the Lake Nyos incident where an 8-10% concentration killed 1700 people. The gas killed all living things within a 15-mile radius of the lake.
Yes 150 people produce lots of CO2 over time but this sort of instantaneous raising of the concentration needs to be carefully judged.
Exhaled air during normal deep breathing contains 4% CO2 and mouth-to-mouth "panting" a lot closer to the ambient 0.4%. Increased CO2 in the bloodstream actually promotes deeper and heavier breathing so for resuscitation it is good. For higher concentrations it works the other way and you ingest even more as you get poisoned.
Posted 31 July 2012 - 09:40 AM
However IF this issue of CO2 in orchestra pits was that dangerous then we would all know about it. The gas must escape or it would cool off and sink into the lower basements. I recall Brian(?) posting some snaps of a CO2 "curtain" or fog coming off an LX bar or similar in a club yet nobody died.
Possibly the fact the air handling kit changed the air fast enough to prevent the saturation becoming to great too quickly. Brian mentioned the figures above producing a saturation of 1% and I presume that would be a "static" volume. Presumably in a real world situation the doors would be opening almost non stop and the ac working continuously.
Presumably the kit comes with method statements and similar so there would be caveats in abundance?
(In any event (groan) I can think of far worse (if not exactly lethal) gases emanating from an assembled host of 150 Sweaty Betties...)
Posted 14 August 2012 - 10:25 PM
This post has been edited by slipstream: 14 August 2012 - 10:25 PM