Text: Dean Ang / Photos: courtesy of Volvo | posted April 20, 2009 16:20
Amazing how a strip of fabric can save your life
It's amazing how a strip of fabric can save your life from a car crash. Airbags and crumple zones are entirely useless without seat belts. Imagine yourself driving fast and coming to a full stop all of a sudden; before you know it, you're flying through the windshield, or you've just made a mess on your steering wheel with your brain in a pulp. The chances of these things happening to you and your passengers are completely reduced when seat belts are worn. According to the National Highway Traffic and Safety Administration, seatbelts reduce the risk of death for a front seat car occupant by about 50 percent. They're called safety belts for a reason.
What it does
If you are cruising at a speed of 120kph and you suddenly collided with another car while trying to overtake a trailer truck on the highway, your car stops abruptly while inertia causes your body to keep on accelerating at 120kph. In case you don't remember your high school Physics, inertia is the tendency of an object to stay put or continue moving unless acted upon by a directional force. In our graphic scenario, the directional force that will stop your body will be anything in front of you, which is hard as parts of the car normally are, will obviously inflict serious injury. The force can also cause you hurtling through the windshield, in which case the pavement will stop your acceleration by exerting the same amount of force that you began with, instantly killing you. Seat belts intervene to apply the same amount of force needed to stop you, with the difference of spreading it to sturdier parts of your body like the rib cage and pelvis over a longer period of time, minimizing injury.
In the late 1800s, the first type of seat belt was born. It was invented by George Cayley to primarily keep pilots in their seats while doing aerial maneuvers. The automotive industry did see its advantage albeit as an option, not standard until the Saab GT 750 was introduced at the New York motor Show in 1958 with seat belts. The following year, Nils Bohlin, a Swedish engineer revolutionized the automotive industry by inventing the V-type three-point safety belt while he was working as a Safety engineer for Volvo. He found out that the existing Y-type seat belts were not entirely safe. That's why he perfected it geometrically and eventually came out with the V-type three-point seat belt. His invention got patented in 1958 and was immediately made available to all car manufacturers. Nils Bohlin was inducted into the Automotive Hall of Fame as recognition for his contribution to the automotive industry in 1999.
Types of seat belts
Lap: An adjustable strap that goes over the waist. This type of seat belts is commonly seen in rear seats nowadays.
Sash: An adjustable strap that goes over the shoulder. This type of seat belt is not used anymore since it very easy to slip out of in a collision.
Three-point: One continuous length of webbing that goes over the waist and shoulder. This type of seat belt helps spread out the energy of the body over the chest, pelvis, and shoulders.
Five-point harness: This type of seat belt has five points of attachment to the seat which makes it a safer but more restrictive type of seat belt. They are typically found on child safety seats and in racing seats.
Six-point harness: This type of belt is similar to a five-point harness but includes an extra belt between the legs. These are used mainly in racing.
Seven-point harness: Used in aerobatic aircrafts. It consists of a five-point harness with redundant lap-belts to prevent the pilots from lifting out of their seat.
Are you aware of the technology behind your car's seat belts? Ever wonder why they get stuck when you pull them too fast? That actually demonstrates how seat belts should perform. Most seat belts have a locking mechanism known as inertia reel. When pulled quickly, a centrifugal clutch engages as the reel spins quickly, tightening the belt. This function may be secured by a weighted pendulum or ball bearing; when these are deflected by sudden deceleration or roll-over of the vehicle, they lock into notches on the reels and stop the belt from further extending.
Types of inertia reel type seat belts:
No Locking Retractor (NLR): Commonly used in recoiling lap belts
Emergency Locking Retractor - Vehicle Sensitive (ELR-V): A mechanism that is sensitive to the vehicle's motion, and is activated by deceleration or rollover of the vehicle.
Emergency Locking Retractor - Vehicle and Webbing Sensitive (ELR-VW): Also sensitive to the wearer?s motion, this is activated by deceleration or rollover of the vehicle or by fast acceleration of the strap from the retractor.
Most modern seat belt assembly today works together with a pretensioner. The pretensioner locks the seat belt in place to limit the wearer's travel inside the car in the event of a crash. The three types of pretensioners that are used today are mechanical, electrical, and pyrotechnic.
Some systems use load limiters to minimize injuries that are caused by seat belts. Load limiters release excess belt webbing when a great amount of force is applied to a belt. The simplest form of a load limiter is a fold sewn into the belt webbing; the stitches break at a a certain amount of force and the excess webbings spread out, extending the belt for a little bit more.
Despite the importance of seat belts, we seldom pay attention to its nuts and bolts when purchasing a car. Seat belts in their current form are so basic that motorists apparently find them dismissible. In a report by the Land Transportation Office (LTO) in 2008, in NCR alone, the number of motorists apprehended for violating the R.A. 8750, otherwise known as "Seat Belts Use Act of 1999", has risen by 102.45% compared to the previous year. While it may seem like there is little left to improve about them, more advanced safety devices are surely underway, just as new inventions like hybrid cars are being released. Perhaps as they improve in technology, they will also get stylish enough to induce this trend-conscious generation to, finally, buckle up.