Triggering of belt tensioners and airbags

The triggering of belt tensioners and airbags in the Mercedes E-Class (4th generation W212, 2009–2016) follows the most modern safety standards. This article describes when and how these systems become active in an emergency. The precisely coordinated technology offers maximum protection for all occupants. Trust the innovative safety technology of the E-Class.

Important Safety Notes

WARNING

After an airbag has been triggered, the airbag components are hot. There is a risk of injury!

Do not touch the airbag components. Have a triggered airbag replaced immediately at a qualified specialist workshop.

WARNING

Pyrotechnically triggered belt tensioners are not functional and therefore cannot protect as intended. There is an increased risk of injury or even death!

Have the pyrotechnically triggered belt tensioners replaced immediately at a qualified specialist workshop.

Mercedes-Benz recommends having the vehicle towed to a qualified specialist workshop after an accident. Take this into account especially after a belt tensioner or airbag has been triggered.

Belt pretensioning triggered by PRE-SAFE in a hazardous situation is performed by an electric motor. This process is reversible.

When a belt tensioner or airbag triggers, you will hear a bang and powder dust may escape. The restraint system warning lampcomes on.

Except in rare cases, the bang does not affect your hearing. The escaping powder dust is generally not harmful to health, but it may cause brief breathing difficulties in people with asthma or respiratory problems. If it is safe to do so, leave the vehicle immediately or open a window to avoid breathing difficulties.

Function

In a collision, the restraint system control unit evaluates important physical data of vehicle deceleration or vehicle acceleration during the first phase of the collision, such as

• Duration
• Direction
• Intensity

Based on this assessment, the restraint system control unit triggers the belt tensioners in the event of a frontal or rear impact.

A belt tensioner can only be triggered if

• the ignition is switched on
• the restraint system components are ready for operation, see "Restraint System Warning Lamp"
• the belt tongue is latched in the buckle on the respective front seat.

The belt tensioners in the rear are triggered regardless of whether the seat belts are latched.

If the restraint system control unit detects a higher accident severity, additional restraint system components are activated independently of one another in certain frontal impact situations:

• Front airbags and driver's knee airbag
• Windowbag, if additional protection potential beyond the seat belt is predicted for the vehicle occupants

Depending on the person in the front passenger seat, the front passenger airbag is either deactivated or activated. The front passenger airbag can only deploy in an accident if the PASSENGER AIR BAG OFF indicator lamp is off. Observe the information on the PASSENGER AIR BAG OFF indicator lamp.

Your vehicle has two-stage front airbags. In the first deployment stage, the front airbag fills with propellant gas, reducing the risk of injury. If the second deployment stage is then activated within a few milliseconds, the front airbag fills with the maximum amount of propellant gas.

The activation thresholds for the belt tensioners and airbags are determined by evaluating the vehicle decelerations or vehicle accelerations occurring at various points in the vehicle. This process is predictive in nature. Deployment must take place in time, at the start of the impact.

Vehicle deceleration or vehicle acceleration and the direction of force are essentially determined by

• the force distribution during the impact
• the collision angle
• the deformation characteristics of the vehicle
• the nature of the object the vehicle collides with.

Factors that only become visible or measurable after the collision do not influence airbag deployment. They are also not an indication of it.

The vehicle can be significantly deformed without an airbag deploying. This is the case when only relatively easily deformable parts are struck and no high deceleration occurs. Conversely, an airbag may have deployed even though the vehicle shows only minor deformation. This is the case, for example, when very rigid vehicle parts, such as side members, are struck and the deceleration is thereby high enough.

If the restraint system control unit detects a side impact or rollover situation, the corresponding restraint system components are activated independently of one another, depending on the type of accident developing.

• Sidebags and pelvis bag on the side of impact, independently of the belt tensioner and of seat belt use

  Vehicles with automatic child seat recognition in the front passenger seat: Front passenger side sidebag and pelvis bag deploy under the following conditions:

  • The front passenger seat is detected as occupied, or
  • the belt tongue is latched in the buckle on the front passenger seat.
• Windowbag on the side of impact, independently of seat belt use and regardless of whether the front passenger seat is occupied
• Belt tensioner, if additional protection potential is predicted for the vehicle occupants in this situation
• Windowbags on the driver and front passenger sides in certain rollover situations, if additional protection potential beyond the seat belt is predicted for the vehicle occupants

Info

Not all airbags are triggered in an accident. The various airbag systems operate independently of one another.

The operation of the airbag systems is determined by the detected accident severity, in particular the vehicle deceleration or vehicle acceleration, and the type of accident that is developing:

• Frontal impact
• Side impact
• Rollover

The interaction of belt tensioners and airbags in the Mercedes E-Class W212 (model years 2009–2016) is designed for maximum protective effect. The systems respond within milliseconds to accident situations and thus provide reliable restraint for the occupants.

The intelligent sensor system is particularly impressive: it analyzes the severity and type of the accident and activates the appropriate restraint systems in a targeted manner. In this way, the E-Class sets standards in active and passive safety.

Question: When do the belt tensioners and airbags deploy in the E-Class W212?

Answer: They deploy in certain frontal, side and rollover situations when the sensor system detects a high deceleration or acceleration.

Question: What happens after the restraint systems have deployed?

Answer: After deployment, the airbags and belt tensioners must be replaced at a qualified specialist workshop, as they have lost their protective function.