The public is told “Wear your seatbelt”, and many do. But few understand the additional phrase “Wear your seatbelt properly”. Often because few people understand what that additional phrase means.
Recently Gorski Consulting came upon a driver of a commercial vehicle wearing a seatbelt as shown in the above photo. Apparently this belt was being worn over many months in the manner shown above. This scenario occurred in a large commercial vehicle. So what is wrong about what we see in the above photo? Well, let’s do a little analysis.
Seatbelts are great devices that have prevented monumental numbers of deaths and lessened the severity of far more injuries. Yes, seat-belts prevent ejection from a vehicle and that is beneficial, but that is not the only benefit.
When worn properly seat-belts anchor an occupant’s body to the vehicle structure. What is meant by the phrase? We mean that we gain a benefit from our seatbelt when it does not contain any slack in the webbing and that it is pressed firmly against an occupant’s body. When no slack exists the occupant’s body is anchored to the vehicle structure so that when the structure of the vehicle decelerates in a collision the occupant’s body also decelerates Almost at the same time. But why is that important? Here we introduce the concept of “The Second Collision”, or “The Human Collision”. These descriptions were coined by researchers many years ago.
When 2 vehicles collide they are involved in the first collision. In others words they enter into a rapid deceleration. This first collision can be completed in as little as 100 milliseconds (1 tenth of a second) or this might be prolonged to as many as 300, or even 500 milliseconds on rare occasions. The bottom line is that the first collision occurs rapidly and this produces the high forces and accelerations that have the potential to cause injury. Remember that just before an impact vehicle occupants travel at the same speed and direction as their vehicle, or they possess the same velocity as their vehicle. With the rapid deceleration of the vehicle its interior also decelerates rapidly. Meanwhile, the occupant’s body continues along at its pre-impact velocity until it strikes the vehicle interior. Occupant motion with respect to the interior can begin in about 60 milliseconds. And here is the important part: What injury you sustain will be dependent on the difference in velocity between your body and the vehicle interior. In some sense, the severity of that first impact between the vehicles is not what causes your injury. Your injury is created when your body collides with the vehicle interior. And this is why it is called The Second Collision.
So the benefit of a seatbelt is to alter the severity with which your body makes contact with the vehicle interior. When the seatbelt is worn firmly against your body the belt becomes a part of the vehicle structure so that when that structure begins to decelerate the seatbelt begins to decelerate. And if your body is firmly against the seatbelt it too begins to decelerate at a similar time as the vehicle structure. So the benefit of this happening is that your body begins to decelerate earlier in the crash pulse. At this time the kinetic energy possessed by your body is dissipated more so in this early portion of deceleration than at times late in the pulse. So by the time your body begins to move toward impact with the vehicle interior it has already lost a substantial amount of its velocity. So the difference between the velocity of the vehicle interior and the velocity of your body is is less, the severity of that impact is less and you sustain less severe injury. That is the benefit of a properly worn seatbelt. But it needs repeating: the seatbelt must be worn firmly against your body in order for it to be beneficial in reducing the severity of your injury.
So now go back and look at the above photo and consider what we have. The lap webbing is positioned well in front of the occupant’s pelvic region. This is an obvious problem because when the vehicle interior begins decelerating, there is a time delay as the occupant’s body catches up to the seatbelt webbing and then the webbing begins to decelerate the occupant’s body – much too late to be of any benefit. Bu the situation is even worse than that.
It has long been known that occupants can sustain abdominal injuries from “submarining” under a lap belt. This can occur when the occupant places the webbing too high above the illiac crests of the pelvis. But another way this occurs is when the lap belt contains slack while there is little slack in the shoulder (torso) webbing. So what happens is the upper body is restrained by the shoulder belt but the lower body is not – and the occupant’s lower body slides underneath the lap webbing. This is a classic mechanism of abdominal injury and resultant death.
So through improper use of the seatbelt the occupant in the above photo is not only gaining no benefit from the restrain but the occupant is actually increasing the likelihood of severe injury, more injury than if no restraint was worn at all.
But why is the lap webbing lying in the manner that it is? The buckle should be well behind the position where it is positioned. The two photos below explain why.
As seen in the above photos someone was inconvenienced because the stock of the seatbelt was falling toward the floor and it was difficult to reach down and pull the stock up so the seatbelt could be buckled. So one decided the solution was to attach the stiff plastic tie onto the frame of the seat and onto the stock so the stock would stay up where it was reachable by the driver. This ingenious solution is a safety disaster. Whoever installed the plastic tie knew nothing about occupant safety. It was an arrangement that would be disastrous if the vehicle was involved in a significant collision. Why did this occur?
In our view it occurred because too many persons are told to “wear” their seatbelts but not enough persons are told to wear them properly and too few understand how to wear a seatbelt properly. And when persons sustain injuries from their seatbelts the gossip spreads that seatbelts are dangerous, etc. Despite decades of seatbelt existence, to this day, there are still numerous persons sustaining seatbelt injuries because they did not understand the safety issues.
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