This fire extinguishent reduces the atmospheric oxygen concentration to less than 15% which is 'acceptable for human exposure over a short period of time'. All of the information I have found says much the same thing without being specific; does anyone know what the short period of time might be? LB

Thanks, Phil That is the information I am more familiar with; I guess it comes down to exposure time, which is the root of my query. LB

Hi LB, I presume that by the nature of the way the aragonite works that the change from ~21% to "less than 15%" would need to be almost instant to control the fire. I would be also interested in how much less than 15% the atmosphere is changed to, i.e is it 14.5% or 3%? Distances to exits would be the telling answer i suppose, especially if the exits are far away, or you turn the wrong way due to hypoxic confusion as demonstrated in the 12 - 15% band above, however if you bump your head whilst escaping, and collapse, how long after the discharge is the room atmosphere back to near the 21% that we all know and love. More questions than answers for you I'm afraid, but a great topic!! Cheers Phil

According to one well known website 'Argonite' is a brand name and registered trademark for a mixture of 50% argon and 50% nitrogen used as an inert gas in gaseous fire suppression systems. As an aside, shortly after joining HSE in 1977 I observed a court case which stemmed from an investigation by my boss of the death of a fitter from asphyxiation in a sub-surface valve pit at an oil platform construction yard in Northern Scotland. As there had been a leak of argon (one of the gases distributed in underground pipes around the yard for welding processes) from a valve, the atmosphere within the pit - a confined space - had become flooded with argon. Though the case was defended, the prosecution was successful as the sheriff agreed from the evidence that the firm had not taken sufficient precautions to ensure the man's safety for entering and working in the pit. However, there's probably a considerable difference between a valve pit unknowingly flooded with argon gas and workplaces where Argonite may be introduced as a fire suppressant under controlled conditions.

I always take these sorts of figures with a huge pinch of salt. First of all, they are reliant on being in that concentration for long enough for symptoms to appear. One lungful of a very low oxygen level is believed to be fatal, without symptoms. The other reason I am sceptical about the lower end of the range is to ask - how did they get this data? How reliable is it likely to be? Go to this page and choose 'decompression chamber' to see Michael Portillo experience a low oxygen environment http://www.bbc.co.uk/sn/...x/executions/near_death/