Lesson 2/Learning Event 1
. The Automatic Chemical Agent Alarm
and persistent chemical agents when they are in vapor or inhalable aerosol form.
Capabilities. The Automatic Chemical Agent Alarm is an automatic miniature chemistry laboratory
which continuously samples the air. The alarm sounds when it detects the following chemical
Nerve agents - V and G
Blood agents - AC, CK
The M42 alarm unit, when connected to the M43 detector unit, provides a remote signal whenever the detector unit senses a
chemical agent. The signal can be either audible and visual (horn and light) or visual only (light only).
Limitations. The Automatic Chemical Agent Alarm must be serviced after every 12 hours of
operation. The M43 Detector Unit will signal when exposed to heavy concentrations of rocket
propellant smoke, screening smoke, signaling smoke, engine exhaust, or in the event of nuclear
Description. The components of the Automatic Chemical Agent Alarm are described below.
The M43 Detector Unit senses the presence of chemical agents in the air and produces an audible
signal. The hand crank located on top of the detector unit is used to manually prime the fluid
system. The air inlet assembly in the open position allows air to be drawn into the detector unit for
sampling. A zero adjust knob is used to set the detector unit during preoperational and operational
procedures and to reset the unit after an alert has been sounded. The horn vol-battery test knob,
when rotated, varies the horn output level from minimum to maximum. When the horn vol-battery
test knob is pressed, the meter located on top of the unit will give a visual indication of the power
The M42 Alarm Unit, when connected to the M43 Detector Unit, provides a remote audible and
visual signal or visual signal only whenever the M43 Detector Unit senses a chemical agent. The
M42 Alarm Unit contains a three-position rotary selector switch which allows manual selection of
test, horn off, or horn on. To operate in the horn off or horn on position, the M42 Alarm Unit must
be connected to an operating M43 Detector Unit.