That and the 'ol carbide cannons.
   Warrant Canary creator

   On May 22, 2017 4:35 PM, "jim bell" <[1]jdb10987@yahoo.com> wrote:

   I am reminded of some experiments I did around 40-45 years ago, filling
   relatively small  (1 foot diameter) balloons with stoichiometric
   [2]https://en.wikipedia.org/wiki/Stoichiometry     mixtures of hydrogen
   and oxygen (or another fuel gas and oxygen, example propane), if
   ignited they produce remarkably loud-sounding, and yet low-pitched
   "booms":  Sounded like a huge explosion done a long distance away.
   Yet, there was no possibility of shrapnel, other than a thin rubber
   membrane.    This could easily scare people in a crowded venue, causing
   panic and crushing crowds.
   Perhaps this explains what is being reported as happening in the
   Manchester arena.
                 Jim Bell

References

   1. mailto:jdb10987@yahoo.com
   2. https://en.wikipedia.org/wiki/Stoichiometry