Opening the upper doors on a vehicle on its side is difficult as the full weight of the doors has to be lifted. For this reason, it may be necessary to use a ladder to lift the doors from above, but this can only be done once the vehicle is fully stabilised. Alternatively, once a team member has gained access, they can push the door from below.
The doors can then be held open either by use of blocks or wedges or they can be tied in the open position. Vehicle Extrication - THE NEXT GENERATION provides a full description, data sheet and FULL LENGTH HD video link to this and many other popular processes and techniques.