In the 1960s Early 1970's, and before there were 2 ways to have a fire go to greater than a 5th Alarm. A "Brough Call" where in an alarm or multiple alarm was transmitted over the old firehouse Alarm Bell system was transmitted in a Brough other than the Brough the 5th Alarm was in to have additional units respond, normally just Engine Companies. Example 6-6 2-2 198 7-7 5-5 598 = A 2nd Alarm assignment for (Manhattan =6-6), box 198 was to in fact respond to Brooklyn = 7-7 (5-5 = 5th Alarm) at Brooklyn Box 598 Resulting in a 7th Alarm assignment.
The 2nd was a "Simultaneous Call" In these cases a distant box or multiple alarm was transmitted in an area away from the fire BUT in the same NYC Borough to provide units, once again normally just Engine Companies above the 5th Alarm. This was under the old Bell alarm system and designed before FDNY Apparatus's had radios. I both cases it was a quicker way for the FDNY dispatchers to send companies to a fire great than 5 Alarms. Now with computer dispatching this is no longer necessary, but still interesting,
Captain Bob Rainey FDNY Engine 26 retired