> I have seen the effect of a busted pipe in the firebox, and what you 
 > suggest is the same as a busted feedwater pipe. The sudden influx of 
 > moisture(water) into the firebox, causes rapid expansion of that 
 > moisture. The firebox will be blasted with a sudden pressure surge, 
 > and may or may not rupture it's sides. The fire will go out, sure, 
 > but the damage will have already been done. Hopefully fire and parts 
 > don't get slung out of the building.
Wayne,
 The fuseable plug in the boiler firebox is very common. I've seen it in 
antique steam traction engines and oil and gas-fired boilers. The fireboxes 
aren't sealed, so they won't rupture. Even if severe damange is caused to the 
boiler, it's almost certainly less than if the boiler itself explodes.
I saw a reprint of a newspaper article from about 1910 that described a 
boiler explosion during threshing. It killed one person outright when one of 
the 7' diameter wheels of the engine hit him, and another 2 or 3 died within 
days from the various effects.
Steam boilers, especially those operating at higher than 15 PSI, are nothing 
to be messed with.
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