Since explosions in model boilers are exceedingly rare anyway, I don't think there is a great deal to be concerned about.
The only actual explosion in a model boiler that I have ever found out about was a model liner that blew up and sank about 1909. It would be fair to say that the construction of that boiler was somewhat deficient, to put it mildly. There was more recently (well, within the last 40-50 years…) a model loco boiler written up in ME that failed (but not explosively) due to being totally choked up with lime.
So provided the boiler is made properly to the relevant standard, and inspected regularly, there would seem to be very little risk. I suspect there is far more risk to the passengers and by standers from the actual derailment, eg broken arms and the like from the fall if the trollies go over too.
John