I am one of those who basically thinks that given the circumstances and recent events, that the HT was right.
I am not a teacher.
I was, however, a pupil in a school in the late 1980s when there was a fire during the school day. In the week before this, some first year boys had been messing about with the fire alarms, and set fire to the stage curtains. I was in a History class when the fire alarm sounded for a few minutes, then stopped ringing. This happened several times and the teacher told us to stay put. Before long, we could smell smoke, so the pupils followed fire drill, left the building and went to the assembly point. The History teacher stayed put.
From the assembly point we had a good view of the fire in the Science Block.
The Science teachers were setting off the fire alarms, and the janitors kept switching them off because they assumed it was kids messing about again!
If what the DD reports is accurate, then I actually think the HT was pretty restrained in their comments. An email supporting the school in their efforts to instil in their pupils an awareness of fire safety and evacuation procedures would be a positive thing to do.
Oh, and when I started school at age 5 I learned lots of interesting words, including fuck and cunt. Scum, to be fair, is pretty mild.