The first letter identifies the apparatus type; E for Engine, M for Medic, L for Ladder, BC for Battalion Chief, I for Inspector, C for Chief, etc.
The first number, designates the county. 1 is for Benton County, 2 is for Franklin.
The second number designates the department; 8 is for Kennewick. 7 is for Richland, 1 is for BCFD1, etc.
The third number is the type of apparatus; 1 for Type 1 Engine, Type 2 Medic, Type 3 Engine, etc.
The last number identifies the station. 1 through 5.... 6 being a reserve unit.
Example: E1815 would be a type 1 Engine from Kennewick Station 5, M1822 is the medic unit from station 2.