Well it would be devastating if enough flammable material was released into the air and ignited by an external ignition source. The danger is not just the blast and heat, but it also sucks out all the oxygen in the blast zone, which suffocates anyone who survived the initial blast.
Hmmmmm.
So, how long does it take for air to rush back in where the blast occurred?
Can't people hold their breaths for 1-3 minutes?
Sounds pretty devastating regardless.