Pretensioner Units are Key to Proper Seat Belt Operation
Automobiles have many different safety systems installed as standard parts of modern vehicles, from front and side airbag systems to seat belts, anti-lock braking devices, and state-of-the-art driving assistance systems that help us keep our vehicles safely on the roadways. When we hear that a vehicle we’re purchasing has either the latest electronic safety feature as an optional add-on or a mandatory safety item like seat belts, most people assume that all the parts necessary for that system to work properly are included. One instance where that is too often not the case is the presence (or lack) of seat belt pretensioners being attached to all the seat belts in a vehicle. The lack of pretensions can and should be looked on as a type of seat belt defect in vehicle design.
What Are Seat Belt Pretensioners and How Do They Function?
When many people hear the term “seat belt pretensioner” they think of the seat belt retraction system included with most all modern seat belts that draw in the slack in harness and lap belts when we first buckle up. Although these retraction systems are certainly important in keeping extra slack out of the belt, they are something different from the seat belt pretensioners that are triggered in a crash. These seat belt pretensioners are tied to the same or similar systems as vehicle airbags and are designed to be activated in response to an actual car crash.
This web page from Clemson University helps explain what pretensioners are and how they function. There are three basic types, defined by how they are triggered in an auto accident:
- Mechanical Tensioning Systems, which are uncommon and are based on powerful springs that tighten and lock the seat belt.
- Electrical Tensioning Systems, which are somewhat more common and use electrical motors to tighten and lock the belt.
- Pyrotechnic Tensioning Systems, which are the most modern and most common type of seat belt pretensioner, using pyrotechnic charges similar to those in airbags.
The airbag systems in modern automobiles are tied to devices that detect sudden changes in speed — called accelerometers — that are used to trigger the pyrotechnic charges that inflate the airbags. Electrical and pyrotechnic safety belt tensioning systems use the same types of accelerometers to trigger the belt locks and tensioners when a collision occurs. In fact, what is typical in current systems designs is to tie the seat belt pretensioner to the same triggering system as the airbags so as to time the seat belt tensioning and the airbag inflation to one another for optimal safety.
Why is a Lack of Pretensioners a Seat Belt Defect?
The presence of seat belt pretensioners significantly improves vehicle occupant safety when a collision occurs. A study by the National Highway Traffic Safety Administration found that drivers and front seat passengers had a 12.8% lower fatality rate in vehicles with pretensioners. Earlier similar study findings were a primary reason why virtually all passenger cars, light trucks, minivans and SUVs in the U.S. were being equipped with front seat pretensioners by model year 2008.
Although the significant safety benefits from pretensioners resulted in rapid and widespread adoption of front seat pretensioning systems, the devices were never mandated by NHTSA, and many recent-model vehicles still do not have pretensioning systems for rear-seat passengers. This website has provided a lookup tool for recent model years that shows which vehicles do and do not have pretensioning systems.
The lack of a simple and widely-used device that has been shown to reduce fatalities by as much as 12.8% is a significant concern, and any death or serious injury that occurs to a rear-seat passenger in a vehicle not equipped with pretensioners should certainly be carefully reviewed as a potential seat belt defect case.
What Types of Injuries May Result from Missing Seat Belt Pretensioners?
Two types of injury mechanisms are of most significant concern in vehicles lacking rear-seat pretensioning systems. In instances of sudden forward deceleration — where the vehicle containing the injury victim suddenly hits an obstacle ahead of it, or where the vehicle is propelled forward by a hit from the rear and then strikes something ahead — the lack of belt pretensioners can result in “submarining.” Submarining occurs when a loose belt allows the victim’s body to slip underneath the restraints, with the lower part of the body moving forward and impacting the rear of the vehicle’s front seats. Submarining can result in serious or fatal injuries, typically to the legs or lower spine. Submarining instances where the entire body slips underneath the loose belt can result in upper body and upper spine injuries, or even decapitation.
When a shoulder harness is lacking a pretensioner, an impact from the side of the vehicle can result in the victim’s body moving a greater distance laterally with a greater force than if a pretensioner was present, often resulting in head or upper arm and shoulder injuries from hitting the inside of the vehicle’s doors or windows.
What is the Reason for Seat Belt Defects from Missing Pretensioners?
Pretensioners are an effective and well-understood safety device. This is the reason for their near-universal adoption for front seat passenger and driver restraints even though they are not required devices under government mandate. Unfortunately, too many recent vehicle models still lack rear seat pretensioning devices for the simple reason that they cost money and many manufacturers choose not to install them.
View this video showing a pyrotechnic seat belt pretensioner being activated:
Sacramento Auto Accident Attorneys
Hello, my name is Ed Smith, and I am a Sacramento Auto Accident Attorney. Safety systems like airbags and seat belts can provide many safety benefits, but only if they are properly designed, manufactured, and actually installed in our vehicles. If you or a family member has been injured in a vehicle accident as the result of a seat belt defect such as missing seat belt pretensioners, please call us (916) 921-6400 or (800) 404-5400 for free, friendly advice.
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Photo by cfarnsworth from Pixabay
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