Heck, we call that "Afterburner rocket booster" here.
Duck and cover? Well, it's probably best to try it, but if there is shrapnel doing 15,000 feet per second, by the time you've heard the boom and started to react, the shrapnel has already done it's damage.
Try it, though, because the blast might be a lot slower, there might be bigger projectiles on (longer) high parabolic trajectories, there could be ricochets, and there might be a slower moving blast/fireball. So I suppose duck and cover is a good thing to do.
However, I have no intention of living my cozy civilian life with a paramilitary state of mind. I refuse to walk around with a constant duck-and-cover reflex in my mind. If I hear a BANG I'll probably jump three feet, then look around to see what it was, and (I hope) go towards it to see if I can help anyone.