Mercedes-Benz GLA 180 Owner's Manual page 57

Occupant safety
54
therefore cannot protect as intended. There is
an increased risk of injury, possibly even fatal.
Have pyrotechnic belt tensioners which have
been triggered replaced at a qualified special-
ist workshop immediately.
Mercedes-Benz recommends that you have the
vehicle towed to a qualified specialist workshop
after an accident. Take this into account, par-
ticularly if a seat belt tensioner was triggered or
an airbag was deployed.
An electric motor is used by PRE-SAFE
ger the tightening of the seat belt in hazardous
situations. This procedure is reversible.
If the belt tensioners are triggered or an airbag is
deployed, you will hear a bang, and a small
amount of powder may also be released. The
6 restraint system warning lamp lights up.
Only in rare cases will the bang affect your hear-
ing. In general, the powder released is not haz-
ardous to health but may cause short-term
breathing difficulties to persons suffering from
asthma or other pulmonary conditions. Provided
it is safe to do so, you should leave the vehicle
immediately or open the window in order to pre-
vent breathing difficulties.
Operation
During the first stage of a collision, the restraint
system control unit evaluates important physi-
cal data relating to vehicle deceleration or accel-
eration, such as:
duration
R
direction
R
intensity
R
Based on the evaluation of this data, the
restraint system control unit triggers the seat
belt tensioners in the event of a head-on or rear
collision.
A seat belt tensioner can be triggered only if:
the ignition is switched on
R
the components of the restraint system are
R
operational. You can find further information
under: "Restraint system warning lamp"
( page 42)
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the seat belt buckle tongue has engaged in
R
the belt buckle of the respective front seat
The seat belt tensioners in the rear compart-
ment are triggered independently of the lock
status of the seat belts.
If the restraint system control unit detects a
high-severity accident, in certain head-on colli-
sions, additional components of the restraint
system are deployed independently of each
other:
front airbags and driver's kneebag
R
windowbag, if the system determines that
R
deployment can offer additional protection to
that provided by the seat belt
On vehicles with the automatic front-passenger
front airbag deactivation system: depending on
the person in the front-passenger seat, the
®
to trig-
front-passenger front airbag is either disabled or
enabled. The front-passenger front airbag can
be deployed in an accident only if the
PASSENGER AIR BAG OFF indicator lamp is off.
Observe the information on the PASSENGER AIR
BAG indicator lamps (
Your vehicle has two-stage front airbags. In the
first deployment stage, the front airbag is filled
with propellant gas. The front airbag is fully
deployed if the second deployment stage is acti-
vated within a few milliseconds.
The activation threshold for the seat belt ten-
sioners and airbags is determined based on the
evaluation of the vehicle's rate of deceleration
or acceleration at various points in the vehicle.
This process is pre-emptive in nature. The trig-
gering/deployment process should take place
in good time at the start of the collision.
The rate of vehicle deceleration or acceleration
and the direction of the force are essentially
determined by:
the distribution of forces during the collision
R
the collision angle
R
the deformation characteristics of the vehicle
R
the characteristics of the object with which
R
the vehicle has collided
Factors that can be seen and measured only
after a collision has occurred do not play a deci-
sive role in the deployment of an airbag. Nor do
they provide an indication of airbag deployment.
The vehicle may be deformed significantly with-
out an airbag being deployed. This is the case if
only parts that are relatively easily deformed are
affected and the rate of deceleration is not high.
Conversely, an airbag may be deployed even
though the vehicle suffers only minor deforma-
tion. This is the case if, for example, very rigid
vehicle parts such as longitudinal body mem-
bers are hit, and sufficient deceleration occurs
as a result.
page 42).
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