Faulty Seat Belts

When it works properly, the seat belt is indisputably the most important safety device in an automobile.  When it works poorly or completely fails to work, the seat belt can cause serious injury and even death. 

Thanks in part to public service campaigns, such as the "buckle up for safety campaign," as well as to mandatory seat belt use laws, Americans now buckle up in record numbers.  Most of us trust that if we are involved in an accident, our seat belt will restrain us and protect us from injury.  In other words, we expect our seat belts to work.  Unfortunately, millions of vehicles on the road have defective seat belt systems, that are incapable of providing reasonable protection in otherwise survivable accidents.   Many of these defects have been known to the auto industry for many years. 

The Basic Principles

A typical auto crash can be viewed as having two collisions.  The "first collision" occurs when the vehicle impacts another vehicle or a fixed object.  The "second collision" occurs when a vehicle occupant impacts the interior of the vehicle or is ejected and hits the ground. The second collision immediately follows, often only by milliseconds, the first collision.  The purpose of a seat belt is to either prevent the second collision or minimize its injury-producing potential.   A snug fitting lap and shoulder belt "ties" the occupant to the passenger compartment and allows him or her to "ride down" the crash, thereby minimizing or eliminating injurious occupant contact with the vehicle interior, such as the windshield, steering wheel or the roof. 

When Seat Belts Fail

In many instances, injury to a belted occupant is due simply to crash forces and the inescapable violence involved in car wrecks.

After all, seat belts cannot immunize us from injury in a collision.   However, in a still significant number of cases, the injury would not have occurred but for a defect in the seat belt system. 

Seat belts fail to restrain occupants due to both poor design and faulty manufacturing.   Some of the more common defects include:

Inertial Unlatching & False Latching. Inertial unlatching occurs when the seat belt becomes unlatched during a collision, allowing the latch plate to pull out of the buckle. Though the auto industry denies that a seat belt can inertially unlatch, recent testing has demonstrated how accident level forces can cause the buckle "pawl" or button to depress and release the latch plate. Millions of vehicles have seat belts that are susceptible to this phenomenon. [Click Here to Link to Inertial Unlatching Issue Page]

False latching occurs when the latch plate looks, feels and even sounds like it is latched when inserted into the buckle but is not fully engaged.   Minimal amounts of force will cause a falsely latched buckle to completely release the latch plate. When a seat belt is falsely latched or becomes inertially unlatched, the occupant is essentially unbelted and unrestrained and moves as though he or she were never belted in the first place.  Such occupants are frequently ejected or found unbelted inside the car.  Though the occupant was properly belted before the seat belt became unlatched, the police report will often list the occupant as being unrestrained.  Cases involving inertial unlatching or false latching frequently arise when either a surviving occupant insists he or she was belted or when other occupants confirm that the deceased occupant was wearing a seat belt.

Torn or Ripped Webbing.  When the seatbelt tears or is ripped in half during an accident, something has probably gone terribly wrong.  Seat belt webbing is designed to withstand the forces of most survivable collisions without ripping or tearing.  Torn or ripped webbing might occur because of a defect or manufacturing flaw in the webbing itself, such as material or weaving deficiencies.

Ripped or torn webbing might also be the consequence of some other vehicle defect.  Any defect that allows excessive slack or payout of the webbing can cause the belt to be "snap-loaded" - loaded too rapidly, which can sever the webbing.  Sharp or protruding edges of vehicle components can also cut through the seat belt.  In one recent case, a bending belt anchor moved the belt into contact with a sharp seat support.

Retractor Failure.   During an accident, the seat belt retractor "locks" the seat belt webbing and holds the occupant in place. When the retractor fails to properly lock, excessive webbing "pays" out of the retractor and results in seat belt "slack."   Sometimes as little as a few inches of "slack" can mean the difference between an injury-free event and catastrophic or fatal injuries.   In a frontal collision, for example, a snug shoulder belt should restrain the occupant in the seat and prevent injurious contacts with the steering wheel and windshield.   A slack or loosely fitting shoulder belt might allow the occupant to move forward and contact these objects.

Retractors can fail to lock because of design defects as well as manufacturing defects.  One failure mode of certain "direct drive" retractors is a phenomenon known as "skip-lock" or "skipping" - which occurs when the retractor lock bar hits the tip of a ratchet tooth and bounces away instead of engaging the root of the tooth and locking the webbing.   Auto manufacturers vehemently deny that skip-lock can occur, but it has been documented in the literature as well as in General Motors' internal research projects.

"Windowshade" Devices. Most U.S. cars manufactured from the late-1970s to the late 1980s contained a "tension-relieving" device in the retractor, which, by design, introduces slack into the shoulder belt.   These so-called "windowshade" devices operate much like a household windowshade - when the belt is pulled out of the retractor, the device engages and the belt remains in its new position.

One consequence of the windowshade design is the inadvertent formation of excessive amounts of seat belt slack.  By design, windowshade retractors permit occupants to intentionally slack into the shoulder belt.  Occupants can also unknowingly introduce slack into the shoulder belt by moving forward to reach for the radio or other item.  As mentioned, slack undermines the effectiveness of a seat belt in an accident and can result in severe head impacts with the steering wheel, dashboard or windshield.

Poor Seat Belt Geometry.  Poor belt geometry can contribute to excessive occupant excursion, particularly in rollovers.  The best location for seat belt anchors is on the seat itself, yet many vehicles have anchors located on the vehicle floor, often behind the occupant's seat.  The resulting shallow belt angle can permit excessive excursion toward the roof in a rollover.  Poor D-Ring locations can also adversely affect geometry and belt effectiveness.  Adjustable D-Rings have improved overall geometry but have only become popular in more recent vehicles.

Vehicle "System" Failure.   To be effective, seat belts must work in conjunction with the vehicle's seats and surrounding structure.   If the seats fail or there is significant roof crush or occupant compartment intrusion, seat belt effectiveness is reduced.   In many accidents, occupants are injured or killed due to a combination of vehicle failures, such as excessive roof crush combined with inadequate restraint by the seat belt.

Door-Mounted and Other Automatic Belt Systems.  These systems pose a slew of safety risks, including occupant ejection when the door opens during a crash and severe spinal cord injuries when an occupant with an automatic shoulder belt forgets to put on the manual lap belt.    [Click Here to Link to Automatic Belt Issue Page]

Lap-only belt designs.  Though the benefits of utilizing a lap and shoulder belt have been known for decades, shoulder belts were not included in the rear seats of most U.S. cars until the late 1980s.  Lap-only belts can lead to fatal or catastrophic injuries, including head, spinal cord and other internal injuries.  [Click Here to Link to Rear Seat Lap Belt Issue Page]

When to Suspect a Seat Belt Failure

Seat belt performance and potential effectiveness is highly dependent upon the facts of an individual accident.   While it is difficult to generalize, the following facts, if present, might indicate a seat belt problem:

•	Both serious and non-serious injuries to belted occupants.   For example, if one belted occupant walks away while another belted occupant is paralyzed or suffers a serious head injury.
•	An injured occupant is found wearing a loose-fitting seat belt.  This could indicate the presence of excess slack.
•	An occupant is found unbelted but either the occupant or other passenger insists he or she was seat belted.  This could indicate inertial unlatching or false latching.
•	An occupant in a frontal collision makes contact with the windshield.  This might indicate the presence of excess slack or retractor failure.
•	A seriously injured belted occupant in a vehicle with limited structural damage.  For example, if there is limited roof crush and limited intrusion into the occupant compartment during a rollover yet a belted occupant sustains head or neck injuries.
•	Serious injuries in a minor to moderate collision.  When a restraint system works properly, occupants typically should not receive serious injuries in minor or moderate speed collisions.
•	The seat belt webbing is torn or ripped or the seat belt is pulled loose from its anchors.  This could be indicative of either a seat belt defect or some other type of vehicle defect.

Evidence that a seat belt failed because of design or manufacturing defects is often subtle and can be difficult to detect.  If a belt failure is suspected, the most important thing to do is preserve the vehicle and the seat belt system since it is extremely difficult to prove that a seat belt failed without the physical evidence.

(09/10/99)