A hybrid has a few other failure modes too. One is called hard start: http://en.wikipedia.org/wiki/Hard_start http://en.wikipedia.org/wiki/Hard_start Another

A hybrid has a few other failure modes too. One is called hard start: http://en.wikipedia.org/wiki/Hard_start http://en.wikipedia.org/wiki/Hard_start Another - nitrous oxide can become explosive in gaseous phase. If enough of it became gas, the oxidizer tank may have exploded. There are also inherent instabilities of hybrids - higher pressure accelerates the burn, which increases pressure, which... We'll know more after they finish the investigation.