Using Seatbelt Pretensioners For Patient Assessment

SUBJECT: Seatbelt Pretensioners
TOPIC: Using Seatbelt Pretensioners for Patient Assessment
OBJECTIVE: Explain how a seatbelt pretensioner system can be used at a crash scene to assist EMS personnel with patient assessment.
TASK: Given a scenario of a crashed vehicle, explain how an analysis of the seatbelt pretensioner system can be used to assist with patient assessment.

Photo by Ron Moore
The driver of this vehicle was wearing a seatbelt at the moment of the collision. The pretensioner fired and prevented the seatbelt recoiler spool from retracting. You can believe these patients when they tell you they were wearing their seatbelts when the accident occurred.

Seatbelt pretensioner systems are designed to instantly remove slack from the seatbelt at the moment of a collision. The intent of this technology is to use the seatbelt to keep occupants out of the airbag inflation zone as the bag deploys. By design, airbags works best if they are fully deployed; unfolded to their full inflation size prior to the occupant making any contact with the airbag. If a front-seat occupant contacts the airbag while it is still inflating and still unfolding, there can and will be injury solely because of the airbag.

There are two basic types of pretensioners, with each using explosive charges to snug the seatbelt. BMW uses a system that lowers the female receiver buckle of the seatbelt shoulder harness system. This movement of the buckle draws the seatbelt tighter across the seated occupant's chest, keeping the person clear of the frontal airbag's inflation zone.

All other manufacturers use a pyrotechnic explosive charge to reverse spin the seatbelt recoiler spool. As this more common pretensioner system fires, the seatbelt spool spins backwards and retracts up to six inches of excess slack from the seatbelt. This style of pretensioner system can now be used by EMS personnel to determine if in fact an occupant was or was not wearing a seatbelt at the moment of the collision.

Photo by Ron Moore
The driver of this vehicle was not wearing a seatbelt. The pretensioner fired and removed all slack from the belt. The webbing will be extremely tight to the touch.

Seatbelt pretensioners deploy regardless of whether that specific seatbelt is being worn or not. This is good for us. Here's the situation. Your front-seat patient has survived a frontal collision. He is outside the vehicle and ambulatory upon your arrival. During your patient assessment, you ask the question, "Were you wearing your seatbelt?" Regardless of what his answer is, if the vehicle is equipped with the recoiler spool seatbelt pretensioner system that has deployed, you need to look and touch their seatbelt.

The first situation you may encounter is finding an unbuckled seatbelt that is displaying as a totally limp belt with excessive slack. If the car door is open, the belt will probably be lying outside, touching the ground. The belt will not retract. This is evidence that the seatbelt WAS in fact being worn at the moment of the collision. The pretensioner fired and "locked" the recoiler spool.

A front-seat pretensioner attached to a seatbelt that was not being worn at the time of the crash will be found straight up and down along the side of the B-pillar after the crash. The seatbelt will be so tight, it will be like a guitar string. The tension and pull on the belt is tremendous. This belt WAS NOT in use at the time of the collision. The pretensioner fired and took all the slack out of the belt. It is impossible to fake this; if the belt is tight, it wasn't being worn!

Photo by Ron Moore
A second clue of an unrestrained driver is the head spider web, high on the windshield. A deploying airbag cannot cause a spider web on the driver’s side.

In addition to a tight seatbelt, a survey of the interior of the vehicle may reveal several other key factors indicating an unrestrained occupant. A bent steering wheel ring is one item to check for. Lift the deployed airbag up and look at the shape of the steering wheel ring.

Second, look at the windshield. A spider web impact on the passenger's side may be due to airbag deployment, but a spider web on the driver's side always indicates occupant impact with the laminated glass. It is impossible for a deploying airbag to cause a spider web on the driver's side of the windshield.

Finally, check the area of the dash at the occupant's knee level. Broken plastic, dented upholstery or bent instrument panels indicate that the knees of the unrestrained occupant slammed into the dash on impact.

Photo by Ron Moore
The final confirmation that your patient was unrestrained is the bent steering wheel ring and the crush damage to the knee bolster area of the dashboard. This driver in fact suffered a left femur fracture and severe head injuries due to her collision with the interior of the car.

It seems that patients always report that they were wearing their seatbelts, whether they were or not. They have this fear of getting a ticket or being fined by the police if they tell the truth and report that they in fact were not belted. Now we have a new best friend - a new technology that can help us verify what the patient is reporting.

To get a second opinion on seatbelt use, check out the interior, but now don't forget to check the status of the seatbelt itself. Report what the patient states to you, but also include on the narrative portion of your patient report, what you observed regarding the seatbelt system. Remember, finding a loose seatbelt after the crash is good; tight is not.

TASK: Given a scenario of a crashed vehicle, explain how an analysis of the seatbelt pretensioner system can be used to assist with patient assessment and determination of seatbelt use or non-use.

Ronald E. Moore, a Firehouse® contributing editor, is the Forum Moderator of the University of Extrication section of the website. Send your extrication questions or concerns to Ron directly at Answers are posted on the U/E Message Center of