Carl F. Thelin

AIRBAG HYSTERIA? WHAT ABOUT SEATBELT HYSTERIA?

            When I wrote the paper “The Airbag Just Fell Out” (below), I wasn’t expecting the hysteria we find about injuries caused by “exploding airbags”. There are many things that old timers like me should have anticipated.

            We knew in the early 1970's that airbags had the potential to cause some injuries to be worse than if the vehicle didn’t have them. But, we also knew some of the things that could be done to reduce the danger.  We ALSO knew, then, that lap belts — without a shoulder belt — could also cause serious injuries. And, we also knew, then, that shoulder belts can cause injuries, too.

            AIRBAGS

            Researchers knew that the driver airbag would present a small problem compared to that of the passenger airbag. The designer could assume that the driver was an adult ranging in size between the 5^th percentile female up to the 95^th percentile male, as demanded by the Federal Motor Vehicle Safety Standard (FMVSS) 208.  The right seat could hold just about anything, including a pair of persons, in a car or truck with a bench front seat. The passenger could be an infant, a child standing on or in front of the seat, a person sitting “side-saddle” talking with the driver — just about anything, even inanimate objects.

            What to do? First, the occupancy of the seat could be roughly established. FMVSS 208 does require that the driver’s seatbelt be buckled; otherwise a buzzer must sound for the first few seconds after the ignition is turned on. Years ago, when the Feds required the ignition interlock, the passenger seat had the same electric-switch seatbelt buckle, and a contact switch under the seat upholstery that would close the circuit only if a person sat there.

            The makers of the Mercedes-Benz (and others) have adopted that idea to direct the computer of a two-stage passenger airbag what to do. If the seat is occupied, but the buckle has no latch plate inserted, the airbag deploys at maximum capacity. If the passenger is buckled, the airbag is deployed with less force because the safety restraint is shared with the shoulder belt.

            Now there is much talk about smart airbag (with computers). It will sense the size of the right seat passenger, the location (seat back or forward on the seat), and the type of the occupant (human, child restraint, or other). All this is achievable, but it will cost more, and take longer to phase in to production.

            LAP BELTS

            For years we fought with the domestic industry about their unwillingness to install lap and shoulder belts in the back seat. Researchers knew that lap belts were primarily to prevent complete ejection. We also knew that shoulder belts could be provided for even the center seat positions. Remember — a few cars and pickup trucks do have bench front seats. How to do it? GM demonstrated that shoulder belt retractor could be imbedded in the roof. Other makers demonstrated that the shoulder belt retractor could be imbedded in the edge of the seatback — and it would work well if the seat was adequately reinforced. An additional advantage of the seatback position is that the shoulder belt will fit better and be more comfortable.

SHOULDER BELTS

            Boy, do we hate to admit it but we knew that shoulder belts could be blamed for enhancing some injuries. Talk about an airbag taking the head off of a child? Shoulder belts can do that, too. Poorly fitted shoulder belts have caused many neck and chest injuries. Finally the domestic manufacturers stopped using the so-called comfort enhancing tension reliever retractors. The snap that occurred when the occupant hit the slack belt was enough to cause serious injury.

            Making the height of the shoulder belt D-ring on the B-pillar is now another way of reducing the injuries that could be caused by a seatbelt on the neck.

Another trick that reduces injuries from seatbelts and airbags is the use of powered pre-tensioners for the shoulder belt. Using the same technology that deploys the airbag, the pre-tensioner causes the retractor to pull in all the slack from the shoulder belt, with enough force to assure that the occupant will be seated tightly against the seatback when the inflating airbag reaches him or her. Here is another place where the occupant sensor is needed. The pre tensioner need not work unless an adult is seated on the seat with the latch plate in the buckle.

            "THE AIRBAG JUST FELL OUT ON MY LAP"

It is ironic. I have been working with industry and government agencies since 1970 to get airbag supplementary restraint systems into cars, vans, and pickup trucks. Now I get calls from lawyers and insurance adjusters who start by saying the client (or claimant) said, "After the crash, I saw that the airbag just fell out into my lap. Why didn't it work?"

            That is one end of the spectrum of the irony. The other end of the spectrum is that I am no longer demanding that airbags be put into vehicles. Now I am reviewing crash test films and nit picking fault with the performance of advanced technology air bags systems in production cars, pickups and vans.

                        BE THANKFUL THAT --

            Back to the persons who say, for instance, their car hit the side of another car while going about 40 mph. Sometimes they claim to be using the seatbelt, sometimes, not.  So I ask the lawyer, "Did she tell you these things herself? She can talk?  Think clearly?"  I ask about the injuries. They are almost always: feet, ankles, knees, hands, wrists and redness on the face. Then I tell the lawyer to tell the driver this, "You wouldn't be telling me this if the airbag just fell out. It came up and then deflated in about one fifth of a second -- faster than you can blink. The airbag only appears to inflate so softly on TV because it was filmed to be shown in slow motion." Be sure to say to your client that, “It saved your face and neck.”

                    WHAT NOISE?

            Then I may hear this, "Well, I didn't hear it explode either." When I crash tested cars equipped with airbags, I sometimes stood near the crash site with my tape recorder. You could never hear the airbag above the loud noise of the crash itself, which is also over in a fifth of a second, despite the long-drawn-out sequences seen in movies.

            Well -- what about the irony of now becoming fussy about the quality of some systems? We see the same fault that we saw when the early examples of seatbelts were being tested. Then, as now, the technical details of the FMVSS 208 standard may permit someone to allow the dummy to submarine (slide down and under) the seatbelt to reduce the impact forces on the head and chest. FMVSS 208 will not allow a car maker to sell a car (for long) if the head or chest forces exceed the limits in a 30 mph barrier crash test. What is the harm? Submarining under the straps allows the narrow webbing to ride up off the hip structure onto the abdomen, crushing the soft tissues.

                     NOW I AM FUSSY

            Now, I see the dummy submarine the airbag. I do not think it is done (or allowed) to reduce the impact forces on the head and chest. The dummy’s legs and hips always slide forward on the seat cushion during the early stages of a crash. The lap belt not only holds the lower torso back, it also pivots about the floor anchorages so that the dummy's bottom end compresses the seat cushion. The lower torso sinks downward, while the head is pivoting around the hips.  The unsatisfactory performance occurs when the seat cushion is short or very soft. The dummy slides ahead and sinks so low that the expanding airbag catches him under the chin and forces his neck into hyperextension. If it was a real person, he would have survived the crash with a clear head, due to the low head forces, but would be unable to move, because of a broken neck.