Most catastrophic failures can be successfully avoided by regular and thorough cleaning, routine inspection, and vigilant attention to the water level.
A steam boiler under pressure contains a tremendous amout of stored energy. Not so much in the steam itself, but in the superheated water (300+ degrees) which flashes into steam when the pressure is abrubtly released. The sudden release of so much energy is what causes all the damage.
So, should we be afraid to be around steam engines? Nope. Show respect, and caution? yes,, but not fear. Knowing what to do (and doing it) to stay out of trouble, is the key. Knowing how to get out of the other scrapes with both you and the boiler intact is a good skill too. An old greybeard once told me, "Never run from a boiler in trouble, or parts of it will catch you."