Report in New Zealand news:-

Six students were injured when a blast ripped through an engineering
classroom about 1pm yesterday.

Four of the students were rushed to hospital in a critical condition
although all but one had improved by today and had been taken off the
critical list.

The blast is thought to have been caused by acetylene leaking from gas
bottles stored in a room behind the classroom.
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I set this metal shop up years ago and taught metalshop in it for
several years. I was terribly distressed today to hear of this
accident. It has made headline news on our national TV and the sight
of my beloved workshop with tin snips driven into the wall, all the
windows blown out by the blast and pools of blood on the floor had me
near to tears.

Question
If acetylene was leaking into the room would you not smell it and be
warned? Would it stay at floor level and not be detected?
It appears the blast was ignited by sparks fron an angle grinder.

I must replace my old rubber acetylene hoses which are cracking.