You can use equipment cards at instant speed as a response to things happening.
Well, I already know this isn't true because Matt has confirmed you cannot play a solar shield in response to a Sun card. (In line with a previous thread you replied to, it follows that jetpacking to a tunnel to dodge a Sun card is also invalid.)
My question is not about a direct response to a storm card (although it is admittedly an indirect response). If I can use a jetpack when buried, I would rather save it until my turn comes around so I know where I want to go. If I can't use the jetpack, the timing really doesn't matter.