i thought it was standard that one of the secretaries grabbed registers and sign in/out log book on the way out. then they hand them to the form tutors, and let them know about the log book if any of their pupils are in it.
maybe they were just double checking, as sometimes kids sign out, but forget to sign back in again.
and are you sure one of the staff didnt already have it? a secondary sch fire drill is big, with lots of staff, did ds1 see someone actually go back into the building and get it? or just retrieve it from another member of staff? highly doubt NO-ONE brought it out really
"Everyone should have designated jobs, so they all don't say 'I thought X ..."
That probably is the case already (though if there have been staff changes, it may be that someone who previously didn't have that task had simply forgotten).
Can understand your anger, but am not even sure it would do you much good to complain - they know they got it wrong and the member of staff might have had a formal reprimand already.
I had been thinking to suggest speaking informally with form tutor (holding back on first idea being to write to the governors) but it's a health and safety issue and having seen their mishandling, in some after-the-event analysis, I suspect that action will already have been taken internally.
It might be something to query after a month or two - they might (if they have sense) have another fire drill to ensure they can do it right, which is for the benefit of the pupils after all, even if it is a touch disruptive.