Re: Halon

[Simon Favre <simon@xxxxxxxxxx>]

Robert A Brady wrote:

>Halon extinguishes flames by scavanging the Hydrogen radicals.  For 
>combustion to continue (propagate), hydrogen radicals are required to split 
>the Oxygen molecules forming an Oxygen radical and a hydroxy radical.  
>
>Halogens such as Bromine and Florine are more reactive with the hydrogen 
>radicals than the O2 is, so they wind up scavanging the hydrogen and thus 
>combustion can't propagate.

Fascinating. I always thought Halon was just displacing the O2. What happens
when you breathe it? Does it bind up the Oxygen radicals, preventing blood
absorption of the O2? Halon (or the newer substitutes) are also widely used
in race cars. Mine has a bottle with 2 nozzles, one between the carbs, and
the other between my feet. I've been debating putting a bigger bottle in the
car, but if the stuff might make me pass out before getting out of the car,
maybe not. The reason the 2nd nozzle is between my feet is because the gas
tank is right above my feet (it's a formula car). The open cockpit and the
low-mounted nozzle may help.

>CO2 and dry chemical extinguishers, on the other hand, work by displacing the 
>oxygen from the fuel.  Water extinguishers work primarilly by cooling the 
>reactants which slows the propagation reactions down to the point where they 
>terminate before they can continue.  Metal fires don't depend on hydrogen 
>radicals to propagate, and therefore Halon is worthless on them.  I'm not 
>sure how you put out a metal fire (i.e. what's in the metal fire 
>extinguishers), but I'd suspect they are some inert ingredient that displaces 
>the oxygen from the fuel.  

Don't they use foam on metal fires? The same kind of foam they use on airport
runways? Halon is not useful outdoors, because the gas dissipates too rapidly.
They can't use water on fuel fires. Water is extremely dangerous on some kinds
of metal fires. I think foam is it.

>Bob Brady, DVAROC
>Recovering Combustion Research Engineer

Still recovering from the burns, eh? ;=)

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