We had a fatality from a central heating plant in this country (NZ) last winter, which is more than we have had from any live steam boiler in any size in over fifty years. We have also had explosions in hot water cylinders, most of which have about 16 gauge copper walls and are never tested or inspected once they go into service.
The effort should be put into the areas where the risk is. The risk with a boiler is proportional to the energy stored. The energy stored goes down linearly with the volume of water contained. It also goes down with the pressure, I think also aproximately linearly. So by the time you get to the sort of boiler that goes into a model boat there is very little risk.
With model locomotives, which generally have larger boilers operating at higher pressures, the risk would be higher….but has there ever been a fatality or serious injury from such a boiler? I know that there have been injuries from actual (miniature) train operation, but curiously enough we tend to see far less angst about the danger from that than we do about the danger from boilers.
Similarly with model boats, I suspect there is actually far more risk to bystanders from a high powered planing hydrofoil than there is from a steam launch. I’ve seen such a boat, radio controlled, climb a fair way up the bank when the driver got confused about port and starboard. I wouldn’t have wanted to be in the way.
regards
John