[LINK] Bush Fire Speeds (was Re: home emergencies)

Brendan Scott brendansweb at optusnet.com.au
Fri Feb 20 14:22:58 AEDT 2009


Pilcher, Fred wrote:
> Was it on LINK or somehwere else where someone noted that the ambient 50
> degree temp was above the flash point of the volatile eucalyptus oils
> and that pockets of the fuel/air mixture were exploding ahead of the
> fire front?
> 
> If that's right, the front could advance much faster than the wind.

[\armchair modeling]

In theory a fire front could spread almost instanteously if the radiant heat of the fire front was sufficiently high? 

The equation would be something to do with the black body temperature of the fire front, the square of the distance from the front, and the specific heat of the flammable materials in the line of sight.  

At each distance from the front would be a time to ignition based on the radiant heat.  At each point there would also be a length of time from the point of exposure to the radiation until ignition and the fuel generating enough heat of its own to ignite other materials through its radiation (perhaps combined with the heat from the earlier front).  This time to ignition would be a function of the ambient temperature, nature of the fuel, temperature of the front and distance from the front. 

There would presumably be a temperature of the front and distance from the front at which this ignition/heat generation period would be sufficiently small at a sufficiently long distance as to permit the (very) rapid ignition and propagation of the front?  

[\end armchair modeling]


Brendan 





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