I've hit on this discussion rather late, but for what it is worth I dealt with a similar scenario the other day
Kurnal has already pointed out some of the common problems with custody suites.
Here are just a few other things then to throw into the mix - things that I encountered. over!
Aggrivating Factors
1) Custody suite was getting evacuated on every alarm activation - causing huge disruption for custodystaff - remedy - designated fire marshalls check panel, investigate if alarm is genuine, custody suite is not evacuated unless absolutely necessary (phased evac plan to be implemented)
2) Insufficient custody staff to evacuate 18 prisoners (this is according the police themselves due to risk of prisoners taking advantage of evacuation scenario and trying to escape ) - Remedy: All available police officers which have otherwise reported to fire assembly point will be on standby to assist custody sergeant and his / her team if required. Prisoners will be handcuffed marched out in a line to assembly point awaiting transport to another police station
3) Detainees can't always be given full body search prior to entering cells due to several reasons (strip searches can only be undertaken if officers have reasonable grounds to suspect the detainee is hiding something about their person) Therefore slim chance detainees could smuggle in lighter / matches small amounts of fuel or other substances which may not get picked up during routine clothing checks .
4) Police Officers are told not to fight fires within the station - also there are no fire extinguishers in custody suite - potential that any small fires could grow into bigger ones - force looking at training certain officers and providing PFFE
5) Large dead end (approx 48 m in one wing of the custody suite) - Impractiacble to add alternative means to reduce travel distances.
6) Corridors leading to cells covered by Heat Detection (possibly back from the days when detainees could smoke in their cells) - Fiorce will change to smoke detection when suite is due for next major refurb.
Mitigating Factors
1) Police Officers are used / trained to deal with extraneous / emergency situations
2) Custody suite, certain cells, adjacent corridors monitored by CCTV - any problems should be picked up very quickly
3) Three ways out of the building from most parts of the custody suite except for cells despite in dead end corridor.
4) Escape routes / corridors kept sterile
5) Custody Sergeant's desk / counter was not cluttered with unecessary paperwork or equipment.
6) AFD to L2 standard.
7) High risk or dangerous detainees are monitored via CCTV in their cell and checked every 15 minutes.

Cell doors will offer nominal protection, holding back smoke and flame.
9) Cells generally sterile with little fire loading contained within them