Lyle, ACCOLC and MTPAS are British internal procedures as Pan mentioned.
ACCOLC (Access Overload Control) is being phased out in 2009. Where the ACCOLC event occurs the cell and necessary surrounding cells are taken out of use to deal with emergency. 999 or 112 calls MIGHT still be made isf the a mobile phone is “within radio range” of other cells not affected by the ACCOLC is imposed. ACCOLC is not a radio dampening procedure it merely prevents access to the network using network blocking of unprioritized non-ACCOLC register
SIM users. Also the Access Control Classes 0-9 and 11-15 were more emphasized. Also certain types of emergency were assigned Gold Silver and Bronze Command authority and priority. Read: (en.wikipedia.org/wiki/Gold_Silver_Bronze_command_structure), how this authroity comes from a centralised authority and then implemented locally.
MTPAS (Mobile Telecommunication Privileged Access Scheme) is similar to ACCOLC but priority is given to privileged users as opposed to ordinary (unprivileged users). Unlike ACCOLC, a MTPAS cannot disable the network but increases resources to MTPAS privileged users. But 999 and 112 calls can still be made by unprivileged users in parallel to an MTPAS event happening.
The network is left to implement MTPAS the best way possible. Gold Commander actions MTPAS events with the network at the local level.
For US issues for 911 look to: (en.wikipedia.org/wiki/P25) and