Union County fire/EMS numbering
Union County uses a slightly confusing system (IMHO).
Its a unified fire & EMS system, however. So, if multiple agencies in a town provide the same services (Union Fire and Union EMU both provide EMS) the number system accounts for this so their numbers are similar but unique (EMU ambulances are 20-1971 to 76 and fire is 20-1977 to 79, for example).
First, number each town 1 thru 21. There are a few other special "towns" beyond the 21 municipalities. These include county hazmat, industrial fire/EMS agencies, commercial EMS providers and the ALS agencies.
1 = Berkeley Heights
2 = Clark
[...]
21 = Winfield
22 = County OEM (HazMat)
23 = Merck
24 = Schering-Plough
25 = Conoco Phillips
31 = Hatzola
32 = Nationwide
33 = On Time
73 = MONOC ALS
74 = Muhlenberg ALS
75 = Overlook ALS
76 = Rahway ALS
77 = Trinitas ALS
Now, if you add a single digit to that, you get a fire or EMS station. Fire stations are numbered from 1 up, EMS stations from 9 down.
11=fire station & 19=EMS station in Berkeley Heights
21=fire station #1, 22=fire station #2 & 29=EMS in Clark
211=fire & 219=EMS in Winfield
241=Schering-Plough Kenilworth, 242=S-P Union, 243=S-P Summit
If you add two digits to the town, you get a fire or EMS unit. Units ending in a "0" are officers (00=fire chief, 10=deputy or battalion chief, etc. except, since EMS is the public-safety stepchild the EMS Chief is 90 and the other EMS officers are 90A, 90B, etc.).
1700=Springfield Fire Chief, 1710=deputy chief, 1720=highest ranking fire captain, etc.
1790=Springfield FAS Captain, 1790A=Springfield FAS First Lt., 1790B=Second Lt.
The other unit identifiers are for vehicles:
31-39 = ladder
41-49 = staff vehicle
51-59 = special apparatus
61-69 = rescue
71-79 = ambulance
81-89 = engine
Prefix a "20-" in front of all of these since we are Union County and that makes our (Springfield) first ambulance 20-1771 and the second ambulance 20-1772.
That said, only a few agencies actually use these numbers routinely. Its supposed to be on all the fire & EMS vehicles (it's on ours) but you'll still hear "Elizabeth Engine 1" or "Summit [First Aid] Squad 2" on the radio.
Oh, and our county issued EMS radios use a different identifer which matches the CenCom CAD system instead.