Removing sealed units from old UPVC windows

[Lincolnshire Ian]

We are getting close to the demolition of our 1960's prefab and thought we would do some preparation before the demo team arrives. 

We would like to remove the sealed units from the ancient upvc windows to reduce the broken glass on site during demolition. 

We can pop out the beading that holds in the double glazing, but the sealed units seem to be stuck in to the frames. We have been able to remove a window, but it has been a very slow business prizing it away from the glue/tape. 

Does anyone have any tips for removing old sealed units that are stuck in to the frames? 

Thanks 

[Marvin]

A photo or 2 would help. I'm surprised that it takes so long. 

[Lincolnshire Ian]

We don't live on site, so I am afraid I don't have a picture. The windows are externally glazed and seem to be stuck into the frames with double sided foam tape.