Thorax airbags are estimated to reduce serious chest injuries in side-impact collisions by approximately 25%. 

The protective effect is obtained by keeping the occupant away from the impact zone, and dampening the blow from the intruding side of the vehicle. Since the occupant is kept away from the intruding vehicle side, protection of the head is also improved. For adequate head protection special airbags are required, however. 

The thorax bag is inflated within 12 thousands of a second; four times faster than a frontal airbag. The bag is inflated at a certain crash threshold, usually corresponding to a speed of the impacting vehicle of more than 15-20 km/h. 

The system consists of a sensor and a module. The module is typically installed in the back rests of the front seats. Some vehicles have their side-impact airbags in the doors. The sensor is placed in the door or in the B-post area and connected to the ECU (Electronic Control Unit) of the vehicle's other safety systems. The bag usually has a volume of only 12 liters to make it as gentle as possible but still efficient enough to provide required protection.