Hi Steve
As Wanderoo posted,it was the Hatch 'Jettison' switch that would blow the hatch bolts.
The switch had to be set 'safe' during after landing checks but after so many years I cannot remember exactly why it was so easy to set wrongly...for obvious reasons us groundcrew never played with the damn thing
I am sure one of the Canberra aircrew on here will explain it for us.
rgds baz