CO2 and Fire Suppression

A few weeks ago, our group attended a mandatory safety class at one our company's facilities. This is where we test some of our products under (almost) real world conditions. Since fire can be a significant hazard during these tests, the majority of the class dealt with the fire suppression system. Basically, if any of the sensors within one of these rooms detects a fire, an alarm sounds, giving you 20 seconds to get your butt out of that room before the doors close and the room is flooded with carbon dioxide. The safety guy made sure we understood that it was important to be out of that room before the CO₂ was released. Of course someone asked the question, "Couldn't we just hold our breath and stay past that 20 seconds?" The safety guy said "No," and gave two reasons. First, the initial release of CO₂ creates an impenetrable fog, which takes a while to dissipate. This makes it easy to get lost, even though the individual rooms are fairly small (about 30' by 20'). Second, and this is where he caught my attention, he stated that in an atmosphere of mostly CO₂, holding your breath does no good since enough O₂ diffuses out through your skin that you would pass out within 15 seconds.

A couple of us looked at each other after that last statement. It didn't seem possible that O₂ could diffuse out of us that quickly since it apparently doesn't diffuse in that quickly, hence the need for lungs. And what about holding your breath underwater? Wouldn't that lead to the same sort of problem? Of course this wouldn't be the first time I was wrong about this kind of thing and so I searched the net for information. As of this writing, I have yet to find any mention of this anywhere. However, I did find that breathing an atmosphere of 10% CO₂ for a few minutes can produce unconsciousness, so perhaps in a 50% CO₂ atmosphere, one or two breaths are sufficient to knock you out. If any of you have an answer to this question, I would love to hear from you. In the meantime, regardless of the answer, you can be sure that when that alarm goes off, I'll be getting my butt out of that room within 20 seconds.