Goodness - this thread is more than a year old!
Even so, I mention that in explanations given me by a doctor concerning my child's asthma; he said that the body urge to gasp a breath is driven more by the CO2 concentration in the lungs, and not by the need for oxygen. A full lungful of an inert gas (Argon, whatever) that does not take part in the exchange to increase the CO2 can leave one asphyxiating, unable to breath unassisted.
Thankfully, my child now grown up, no longer suffers asthma, having learned to not to inadvertently hyperventilate (ie. over-breathe) as a norm.
All inert gases are suffocants! The warnings MUST be heeded. They can cause loss of consciousness and death in confined areas. They must be used with caution!