Dave wrote:

On Sun, 13 Nov 2005 01:54:33 GMT, Rosalie B.
said:

Any gas that displaces oxygen down below about 19% will
asphyxiate you whether it is poisonous or not. For instance Freon or
an excess of nitrogen will both do it.

No doubt about that. I was simply addressing the characterization of CO2 as
a "poison."

Anything in the world is a poison in the wrong quantities. Even
water. So it is really immaterial whether CO2 is a poison or if it
just asphyxiates you by displacing oxygen.

In the case of CO, that really will severely impact your health at
much lower levels than CO2, so I suppose one could call it a poison.

Your 19% figure, by the way, is based on breathing at atmospheric pressure.
When I was diving helium we would go below that level, with the percentage
depending on the depth.

Are you diving with a portable catalytic space heater?
grandma Rosalie