Yes indeed MR, they are evacuated from the cell (with the cell door being closed to retain the fire in the cell) and taken to place of compartive safety. Which means through another fire resisiting door to a 'holding point' to prepare for onward evacuation.
I can only comment on law courts in Scotland. The common feature is the application of legislation and standards by the same Enforcing Authority (the Chief Inspector of Fire & Rescue Services). The differencing feature is 'sleeping accommodation', with court cells not being designed nor intended for sleepinig purposes, unlike prison cells which are (to an extent) 'residential' accommodation. (this difference is best recognised in terms of fire loading within the cells. In court cells the occupancy factor can be high (court throughput) but the fire loading low (no domestic features), whereas a prison cell could have two occupants with all their domestic paraphenalia).
Another distinction is what actually happens in the Court itself, where reaction to an alarm of fire relies on direction from the 'Bench'.