Volvo VNL 780 Operator's Manual page 67

SAFETY INFORMATION 57
The inflatable airbag is folded into the center of the steering wheel. It inflates in the event
of a serious collision above a certain level, where the angle of impact, crash severity,
speed and nature of the object involved in the collision all play a part in whether or not the
airbag is activated.
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The system consists of a gas generator surrounded by the inflatable airbag. In the event of a
sufficiently violent collision, a control unit activates the gas generator ignitor and the airbag
inflates. To cushion the impact, the airbag deflates when compressed. This also releases
some nontoxic smoke into the cab. The entire sequence, from inflation to deflation of the
airbag, takes a few tenths of a second.
The SRS system is continually monitored by the control unit. A control unit is mounted on a
bracket above the engine cover which detects deceleration. The control unit also contains
a standby power unit which can supply the system with power for a short time, in case
the normal supply breaks.