This is from the then FD PIO in 2011:
All missions within KCFD, such as EMS, Fire, HazMat, and Rescue, have been integrated into one radio system.
KCFD Communications will now dispatch everything over A-1 Primary
Companies will be informed as to what channel to respond on.
A-3 and A-4 will be used primarily for calls involving a minimal amount of companies or radio transmission.
A-5 thru A-10 will be our TAC channels for fire ground operations, technical rescues or scenarios involving large scale or multiple companies.
This is a rather condensed explanation.
Thanks, Joe V.
Joseph Vitale
Battalion Chief
Public Information Officer