Air bag deployment - misunderstanding of principle

AIR BAG DEPLOYMENT - MISUNDERSTANDING OF PRINCIPLE

Model

All models

Affected vehicles

All vehicles fitted with front mounted air bags (SRS) RE - ISSUE INFORMATION: Help Desk Telephone and Fax details in ACTION text amended. Please destroy your existing copy and replace with this Issue 2.

Date

1999-01-13

Reference

Bulletin 0004, CDS ref L8492bu

Bulletin text

All models

AFFECTED RANGE:

All vehicles fitted with front mounted air bags (SRS)

RE - ISSUE INFORMATION: Help Desk Telephone and Fax details in ACTION text amended. Please destroy your existing copy and replace with this Issue 2.

PROBLEM:

AIR BAG DEPLOYMENT - MISUNDERSTANDING OF PRINCIPLE

Belief that an air bag under certain situations should have deployed, and concern that it may not have been operational.

CAUSE:

The basic principle of an air bag design is as follows: To only deploy in a frontal accident of such force as to endanger the seat occupant WHO IS WEARING A SEAT BELT from coming into contact with the forward interior structure of the vehicle e.g. steering wheel / column. NOTE: The seat belt is the primary restraint and the air bag is designed to provide additional protection.

The critical factors which determine air bag deployment are: • = Direction of impact. = • = Rate at which the vehicle decelerates in an accident. Situations where air bag may not deploy are as follows: • = Side, rear, corner or rollover damage. Such damage may be severe but does not involve heavy frontal impact. = • = Frontal impact where significant damage is evident to the relatively ‘soft’ exterior panels but where the structure, i.e. longitudinal rails, bulkhead, sills and floor, remain largely undamaged. This is particularly applicable where the impact has been above the level of the body longitudinal rails e.g. where the vehicle has partially under-ridden the rear of a heavy goods vehicle. =

Bulletin N o : 0004 L8492bu 2 13.01.99

An effective example which illustrates the need for a carefully designed air bag deployment threshold is in the frequent situation where a vehicle strikes a kerb or minor object before it strikes a major object. Clearly, the air bag is NOT required to deploy when striking the minor object as it will have deflated by the time the major object is struck.

ACTION:

Should an enquiry be received in respect of a front mounted air bag non deployment, the following procedure should be followed:

Examine the vehicle to establish direction of impact. whether seat belts were being worn and if so, whether the driver contacted the steering wheel. If it was not a frontal impact or the driver (wearing seatbelt) did not contact the steering wheel, then the front mounted air bag operated correctly in NOT deploying. If, having considered the above, it is your judgment that the front mounted air bag should have deployed, please contact your technical help desk for guidance.

Help Desks: • = UK After Sales Technical Support - Tel: 0121 781 6500 = • = Dealers outside UK - contact your National Sales Company • = International markets - contact your Import Distributor

PARTS INFORMATION:

Not applicable

WARRANTY CLAIMS: Not applicable

Also ascertain, if possible,

Fax: 0121 781 6398