The M8A1 automatic chemical agent alarm consists of the M43A1 detector unit and the M42 alarm unit. This unit is the primary means of detecting chemical agents arriving in a unit area from an upwind chemical attack. It can detect chemical agents in vapor and aerosol form and can alert personnel by audible and visual signals. It is issued to platoons, companies, and similar units.

The M43 detector unit of the automatic chemical agent alarm continuously samples the air at its location and indicates the presence of nerve agents. The M43 gives an audible alarm. The M42 remote alarm unit provides both an audible and visual alarm when connected by wire to the M43 detection. The M42 audible alarm can be turned off manually. Up to five M42s can be connected to the M43 (fig. 9-6). Maximum cable length must not exceed 400 meters from the detector to the farthest alarm.

Figure 9-7.-Dep1oyment of automatic chemical agent alarms.

Figure 9-7, view A, shows a situation where four detectors are emplaced with three platoons online. Note the orientation on the wind direction. The detector is oriented on wind direction, not on the direction of the enemy. When the automatic chemical agent alarms are mounted on vehicles, consideration must be given to wind direction for the protection of the main body. Figure 9-7, view B, shows an array using four detectors with the wind direction coming from the right flank of the unit. A significant difference between a four-detector may and a six-detector array is that with

Figure 9-8.-ABC-M11 portable decontaminating apparatus.

only four detectors the may must be shifted when the wind direction shifts greater than 20 degrees. Figure 9-7, view C, shows a company in a defensive position with six detectors deployed. The actual number of alarm systems per unit varies depending upon the table of allowance (TOA). The 300-meter distance between the M43 detectors reduces the possibility that agent clouds might drift through holes in the array. This array provides a high probability of detecting an off-target attack within a reasonable warning time.

NOTE

Remember that the detector is oriented on wind direction, NOT on the direction of the enemy.