Pete:

 

Halon works completely different from CO2. It does not remove oxygen from the atmosphere. It works by combining with free radicals produced by the chemical reactions in the middle of the combustion process. Without these free radicals combustion cannot continue to completion and the fire is halted.

 

I have investigated fires occuring in merchant ship engine rooms where Halon was used. It was successful in extinguishing the fire and shuting down all of the diesel engiens drawing air from the engine room. The human engine room crews continued to function in a normal, although rather excited, manner. When CO2 is used in these circumstances, it is imperative to account for all crew prior to release. It is not uncommon for the diesel engines to continue running even though the engine room fire is succesfully extinguished with CO2, but humans remaining in this environment would succomb almost immediately.

 

I have also investigated fires where ventilation was not secured prior to releasing Halon. Sometimes it is successful (if released very early in the fire developement), sometimes it just nocks it down for a few minutes before it re-errupts.

 

Halon was formerly used quite commonly in areas where people could not realisticaly be evacuated, such as race car cockpits. In this instance it could not be counted on to permanently extinguish a fire in the cockpit, but it would nock it down for a minute or so to give the driver time to evacuate.

 

The health downside from Halon is associated with the chlorine compounds that result from its interaction with the intermediary compounds of the fire. These compounds are not a serious problem for brief periods of time and are certainly much better than the alternatives.

 

 

Rob