Fleet Services - Emergency Crew

[RobUK]

The Fleet Services Bureau operate a number of Emergency Crew mechanics around the city anyone advise on the numbering of these units, I've seen mainly 3 digit codes and some two digit " EC xxx" codes - are these related to the staff that operate them as a lone user ride or maybe Borough codes ??
EC 11 seen at E24/L5 and older EC584 seen attending E16 which got grounded in a sink hole