LEVELS AND ZONES
Apparatus warning lights are installed to provide a maximum optical warning to traffic in the vicinity of the apparatus, whether the unit is responding or parked on-scene. The needs while requesting right-of-way (responding) focus on the front of the apparatus and are obviously different than when parked on-scene and the rear is blocking the right-of-way.
To fulfill these needs, you divide the apparatus in two different ways. An upper and lower warning light level is defined, and each side of the apparatus is identified by a letter. The four zones are determined by drawing lines through the geometric center of the apparatus at 45-degree angles. In easier terms, while viewing the apparatus from the top, imagine an equal "X" drawn through the center. The front zone is considered "A" and, moving clockwise, the right side is "B," the rear is "C," and the left side is "D"
WARNING LIGHT PLACEMENT
On larger apparatus, the upper-level warning lights should be mounted as high and as close to the corner points of the apparatus as practical and within the specified height defined by the device manufacturer. This will help define the clearance lines of the apparatus and provide a more distant warning.
The lower-level lights should be as close to the corner points of the apparatus as practical, with the optical center of the light between 18 and 62 inches above ground. Note the phrase "as practical." If your apparatus design does not provide room at the lower rear corner to mount a warning light, the rear portion of the wheel well might be as close to the corner point as practical and will comply with this intention .
In addition, at least one midship optical warning device on each side of the apparatus. Additional midship lights are recommended on longer apparatus, when the distance between the centers of the lower-level lights exceeds 15 feet.
All optical warning devices should include the requirement that the unit be constructed or arranged to avoid projecting the light either directly or through mirrors into any driving or crew compartment. This means that where 360-degree rotating lights are used, the rear of cab light bars should be "blacked out" on tillered trucks or apparatus with a raised crew-cab roof that has forward-facing windows.
On smaller apparatus, the upper-level devices should be mounted as high as practical but not higher than eight feet. They can be combined into one or more enclosures (such as a lightbar) and should be mounted on the cab roof or another convenient location.
The lower-level warning lights should be mounted as close as practical to the front corner points of the apparatus with the optical center between 18 and 48 inches