This happened a while ago (about 2005) - no one was injured as the fuses cleared the fault, the door was shut, and damage was substantially contained within the compartment. Cause was believed to have been the small wiring used for metering connections, of which there is little left.
Went back into service after repairs.
I think the fuse size was around 200/250A but may have been smaller.
In the picture the top connections to the busbars have already been removed. The amazing thing to me is how well the fault was contained (disclaimer:- we manufactured the steelwork!)