[QUOTE=Tuckerfan]
Again, the historical record of people being killed by steam explosions in automobiles appears to be non-existant. I can’t see how a pint of water in the form of steam would be enough to kill somone. (Give them a severe burn, yes.)
[/QUOTE]
A pint of boiling water going to steam, no. But, from your own linked article, at least some Stanley Steamers ran off a 15 gallon reservoir, which is a different kettle.
Leno also goes on to say:
Which is something that I can see happening in a crash at 45-55 mph. Now, some of the spectacular locomotive explosions were caused simply by practices like tying down reliefs and running as hot as they could manage. Others did occur when the pressure vessel’s integrity failed during a crash at normal operating conditions.
Remember - a volume of water transforms into a huge volume of gas, when it flashes to steam. Basic ideal gas law: an ideal gas occupies 22.4 L per mole of gas molecules at atmospheric pressure and 0 Celsius. A mole of water is 18 grams. I realize that both these numbers aren’t exactly valid for water boiling under pressure, nor for what the resulting vapor will expand to, in case of a catastrophic failure of the containment vessel, but I figure they’re good enough to begin to illustrate the magnitude of the problem.
In 15 gallons of water there are approximately 3100 moles of water. (3780 ml/gallon; 18 grams water per ml of water; and rounding to the nearest two digits.) Multiply that by 22.4 liters of gas per mole, and those fifteen gallons of water are going to try to occupy nearly 70,000 liters. A comparatively huge volume.
I can’t put this into proper thermodynamic terms, but IIRC, the way that a failed pressure vessel will fail depends on a lot of things, but the biggest single factor is whether it’s failed in such a manner as to make it able to still retain some pressure on the fluid it is containing, or if the pressure inside the vessel drops to equal that outside the pressure vessel instantly. Paradoxical as it might appear, the smaller leak, with the pressure remaining inside the vessel, is less likely to rupture catastrophically, simply because the small failure does act as a valve, to make for a controlled conversion from fluid to vapor. But a large failure allows all the boiling fluid to flash to vapor immediately, and that has the effect of causing the vessel to explode, as all that vapor tries to expand to its proper volume per ideal pressure laws.
While the ratio of volumes with the smaller volume boiler would be the same in case of a failure, the absolute mass involved does play a factor.
Now, it’s quite possible that, at the pressures involved, a 15 gallon boiling water mass is not going to be able to become deadly. But I don’t know that, and I don’t think you can compare it to the relative safety of a 2 quart boiling mass.
Finally, while there may be no laws against boilers, the NTSB, I believe, has the authority to approve or deny any proposed new street vehicle for the US. And without a background of how steamers behave in test-crashes I can see years spent to get a baseline for comparison before the NTSB signs off modern steamer vehicles.
OTOH, I may be being excessively pessimistic - whatever technologies being used to prevent the possibility of BLEVEs with CNG vehicles may well be suffcient to make even 15 gallon boilers that meet modern safety expectations. You’re just getting some off-the-cuff thoughts from a former steam plant worker. I like steam, and generally I understand it, but it scares me, too.
