IIRC the cockpit canopy jacks were fairly powerful beasts which extended to about 18 inches. In a static jettison they would undoubtedly blow the canopy a fair way up. I certainly remember the canopy whizzing into the air before it started its descent to mother earth.
I also remember a safety lecture where we were shown a graphic pic of a jettison jack neatly inserted into some riggers elbow and exiting out of the wrist. Apparently the canopy was off, he was resting his arm on the cockpit edge when the system (presumably there were no seats in) went orf and bang went his arm! Gruesome stuff. It was a fairly standard lecture - anybody else remember it?