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Astraist
Master Driver



Joined: Mar 27, 2010
Posts: 209

PostPosted: Sat Dec 10, 2011 5:02 pm Reply with quote Back to top

Safety! Safety always comes first, as well we know. Road collisions are a lead cause of death in the western world. This is why car manufacturers are nowadays very occupied with safety issues. This divides into primary or active safety, which is the car's ability to avoid a collision, by being easy and comfortable to drive and control, and by use of systmes like ABS, stability control and such. Most of these subjects have been addressed in previous articles, so we will deal with secondary (or "passive") safety which donates the car's ability to protect it's occupants in a collision.

Big and rigid or soft?
Old cars have the reputation of being big, heavy, rigid and thus alledgly safe. This could not be further away from the truth. Not for nothing are modern cars made to be soft and crumpable. Imagine a perfectly rigid car hitting a wall. It will be stopped at once. However, the bodies of the occupants (Which are not part of the car) will continue to move forward at the speed that the car was moving before it was stopped. As the car decelerates sharply to a stop, the occupants bodies' are in fact accelerating and than hit the steering wheel, dashboard, windshield, etcetra.

Even if seatbelts, airbags and other restraining measures are used to keep the body in place, the internal organs of the human body, mainly the brain and the organs and blood vessels of the stomach, be accelerating untill they hit bone or flesh, causing internal injuries and internal bleedings. At around 200G - serious head trauma is likely to occur.

Now, imagine a softer car. The bumper hits the wall, but since it's soft it gets crammed between the wall and the passenger's compartment. This means that the moment of the collision is stretched longer over time and that the passengers' compartment is actually still moving, as if "into" the engine compartment which is squeezed like the meat of the sandwich. This makes the passengers' compartment stop more gradually and less acceleration forces to be at work.

This is the idea of crumple zones. A big crumple zone is fitted into the front portion of most cars. The engine compartment is made to crumple between two to five feet at a collision, reducing the forces at work. For this sake, the engine mountings are also made to crumple. This has a secondary advantage of allowing the engine to drop, often unto a pre-arranged space, instead of risking it penetrating the passenger's compartment. The same happens with the steering column, which otherwise could pop out and impale the driver.

The rear of the car is typically shorter, and a smaller crumple zone can be fitted into it. This is part of the reason why high-speed rear end collisions are very deadly. Modern cars are simply not made to deal with such blows. A side collision at junctions are also known to be deadly, because the doors are even more slim, so the crumple zones fitted into them are even smaller, causing more acceleration forces to work on the passengers of the car in such a collision.

The passengers' compartment itself is protected by a strong, rigid "safety cage" that prevents intrusion, particularly around the engine's firewall or the side doors. The external surfaces of the doors, floor and roof are made to crumple and disperse the energy of the collision further and around the passengers' compartment.

A now, a bit of trivia! Two identical cars are driving in opposite direction at 60 miles per hour and collide head on. How powerfull will the impact be? Will it's velocity be of 120mph, or 60? The correct answer is 60mph, and the answer is simple. If both cars have the same mass and velocity, they will share the force of impact (a total of 120mph) equally, so each one will only take a force equall of hitting a solid wall at 60mph. This isn't applicable to actual head-on collisions, so it's generally better to collide with whatever is off of the road, rather than with the car in front, but it's important not to treat these collisions as a simple math drill.

Restraints
Nevertheless, crumple zones are not very effective if no restraints are used. The main and most important restraint, in all sorts of collisions, from speeds as low as 5mph, to even high-speed head-on collisions or side impacts, is the seatbelt. Modern seatbelts are three-point belts that combine a main lapbelt with a diagonal belt. The lapbelt is the most important part of the seatbelt and of any restraints whatsoever. It keeps the pelvic from accelerating and hitting the steering or underdash or the door (in a side collision). It should be fitted on the pelvic, not the stomach, where it won't work as effectivelly and apply pressure on the stomach, causing internal injuries.

The diagonal belt is fitted over the shoulder, and is made to keep the upper body from hitting the steering, dash or windshield, as well as prevent the relatively rare occurance of being projected from the car alltogether. This strap should be fitted on the acromion which is the most rigid bony part of the shoulder. Fit it too high and on your collar bone, and it will work but also cause fractures (the collar bone is thin and feeble). Even higher and it will chaft against your neck dangerously. Fit it too low and on your arm, and your body will be allowed to rotate around the belt in a collision and be harmed. The popular under the armpit position is particularly dangerous, with the potential of dissecting the whole arm.

The seatbelt should be snug to provide protection. The lead cause of injuries in collisions is the effect of submarining where the body slides under the lapbelt so the pelvic hits the underdash and the lapbelt squeezes on the stomach. This will occur if the lapbelt is too loose or if it fitted over thick clothing (coats and extectra) where the belt grips the clothes and not the person beneath it.

A partial solution is achieved by using a pretentioner that causes a small detonation that pulls the belt tighter by an inch or two upon a collision (just prior to airbag deployment) and tightens any loose ends from clothes or from driving. It's still a very good idea to avoid heavy clothing, as well as to fit the lapbelt low and tight, and even tighten it every twenty minutes or so.

Another cause of submarining is a reclined backrest, where the body is allowed to slip under the lapbelt. Keep the seat's back relatively erect. In general, the support of the seat itself effects the effectiveness of the seatbelt, where the seat's side support helps prevent pelvic injury in side collisions, which is why modern cars even have their rear seats split up into three seperate seats. Another good reason to avoid seat covers!

Any twists in the belt is unwanted. What happens in a collision is that your body begins to accelerate and than hits the seatbelt instead of the steering wheel or dash. Being flexible and having a bigger overall space, hitting the seatbelt is much softer. However, if a part of the belt is twisted around, than the force of impact would not be dispersed equally, and more force be applied unto the body at that point.

Child seats are made to replace the seatbelt, which are intended for the use of adults, in the weight of over 36 kilograms and height of 145 centimeters at least. Little children are much smaller, and often have a less rigid structure in bones, mainly at the neck in ages of under two years. This is why it's preferable for children to ride against the direction of travel for as long as possible. Booster seats are used for bigger children with the simple intention of boosting their height to the height in which the lapbelt and shoulderbelt can be fitted on the right spot over the child's body.


Airbags
Airbags are another innovation. They really help in places where the seatbelts don't always work as well, and even in situations where the car is somewhat crushed towards the passengers. The airbag is a small detonator (yes, that means explosive) that fires up and causes a holed bag to inflate at a speed of about 321 kilometers per hour. Provided that you are at a distance greater than 10 inches from it and buckled as you should be, it will begin to deflate as you hit it. Again, this is just like hitting the steering wheel, but instead the hit is dispersed over a wider area and against a softer surface. If too close to it or not fastened, hitting the airbag can be just as bad as hitting the wheel.

Further airbags have been added to the dashboard in front of the front passenger, to the inside of the front seats, protecting the pelvic and ribs from hitting the doors at a side collision (where the arm usually slaps the ribs hard enough to cause fractures), and a curtain airbag which helps prevent head injury in similar collisions and in roll-overs (where they remain deployed for a long term of time). Further airbags include airbags in the underdash to prevent knee injury, side airbag between the front seats, airbags in the rear seats and in the seatbelts themselves. Have no doubt - the more the better!

A few additional notes as to the proper use of the airbags: First, they are intended to protect adults and in absolutly no way can a safety seat for children be put in front of front airbags (sometimes the side airbags also cause a problem), and it's preferable to keep children under 14 in the rear seats in general, preferably in the center of the car.

It's forbidden for anyone who enjoys being alive, to put anything in the area in which the airbags operate. Any, even the most slim and minimalistic seat cover, will impade the proper operation of side airbags as to remove their effect of even cause them to blow the backrest! A handfree phone fitted anywhere near the passenger's airbag area (this particular airbag has a hugh coverage and a volume of over a hundred liters), and any GPS or utility on the windshield around it, is forbidden. This airbag inflates against the front windshield, almost as high as the ceiling. It's also a good idea to hold the steering wheel at 9 and 3 because if the hands are held too high, the airbag can hurt them as well as throw them in your face.

Head Restraints
A third and nonetheless important safety measure is the head restraint. Don't under-estimate it, it is vital for your safety! When you are rear-ended, even at slow speeds, the car accelerates forward with the seat and your body in it. However, your head which is not leaned against the seat will "fall back" and this will create strain on the neck, causing a series of injuries, often with long-term effects, including the ominiouos whiplash injury (whose mechanism is not perfectly clear to this day). The head restraint is used to prevent the head from falling too far back, and it's contribution can even prevent you from hurting your forehead or breaking your neck all together.

The head restraint is designed to be fitted up against the thickest part of your head, just below the height of the eyebrows. The restraint is most effective when close to the head and at it's middle portion, so it's best to put it high, so it's center of in line with your eyebrows. Just as important, and sadly much more neglected, is the proper distance from the head. Any distance greater than six centimeters is dangerous. Two or thre centimeters is ideal. Often the restraint itself cannot be adjusted forth and afte or not far enough, but that's no excuse, and to achieve the right result we might need to change the angle of the whole backrest to a more upright one.

The protection offered by the head restraint has been improved by the use of active head restraints, which work much like the seatbelt pretentioners and the airbags, where a detonator moves the head restraint and brings it closer to your head at the moment of the collision. Another measure is a similar intrument that reclines the backrest itself progressively at a collision. This counteracts the forward motion caused by the collision, so the whole back and neck remain stationary and nearly unharmed.

Others
The glasses of the car also form part of it's protection. The front windshield is made of laminated glass which is built of two layers of glass adhesed by a certain polymer in between. This way, the glass only cracks slightly but does not break. This allows to prevent passengers from being projected out of the car. The windows and mirrors are made from strong glass. The interior mirror in particular is made to crumple, too. This prevents any shards from being projected, as well as preventing any kind of head-bob against it. This is why is it connected to the windshield rather than the ceiling. The shards from the side windows are prevented by use of curtain airbags (Which are highly effective!).

Cars are also made to prevent any kind of ignition when hit. The gas chamber is built to be rigid and the fuel injection and electricrity in the car are immediately disconnected at the moment of impact. Many parts, including the seats' fabrics, have a short-term fire ressistant qualities, as do most child safety seats.

Another source of danger is loose objects. Any small suitcase, laptop or even a small bag can turn into a massive projectile weighing dozens and hundreds of pounds, in a collision. All objects should be stored in the trunk. Heavy objects should be placed against the backseats, preferably in the sides. Buckling up the rear seatbelts helps to keep the rear seats to restraint this cargo.

Too heavy cargo which is misplaced can quite easily penetrate through the rear seats. Cargo in the passengers' compartmen should be limited to small, light and soft bags which will either be buckled up or placed in the rear seats on the floor. Unbuckled passengers also act as projectiles and have been well proven to increase the risk of fatality to the passenger in front by two or three times!

Modern steering columns and pedals are made to crumple, too. Before a collision, the driver is most likely to be braking hard and braced against the wheel. At this point, the driver will intuitivelly tighten up and push back from the hazard and into the seat. The muscular tension in the limbs (legs, arms, neck) only increases the risk of injury since the tensed muscles cannot absorb the blow which instead is being projected unto the bones, which are held forcifully by the muscles.

This is particularly crucial if your seat is placed too far back, allowing your limbs to become bolt-straight. In this event, you will suffer from fractures down your arms and legs (rather than having them folded by the forces of the collision) and up to your shoulders and collar bones (at the arms) and the pelvic and even the base of the spine (in the legs). Another problem is driving barefoot or with heels that causes severe injury to the foot itself when the force is hard enough to push the pedals back into the compartment. So, instead, the pedals crumple and drop down, which evens out the push caused by the crash itself, reducing injuries to the limbs.

N.B. Unlike the popular opinion, a perfectly loose body isn't all that good either. This is part of the reason why falling asleep at the wheel is so deadly. A loosened neck tends to drop, which leaves it voulnrable in a collision, but the main issue is with the square stomach muscles which, if tensed, help reduce the amount of internal injuries. If loose, there is a high likelihood of injuries like a ruptured spleen or internal bleedig from the main artery which runs down the stomach.

Pedestrian Protection
So many of the casualties and injuries in road collisions are caused to people who were not even driving, rather to pedestrians. Another problem is that those pedestrians are normally part of more voulnrable parts of the population, either children or elderly, with little boys being at most risk. When hit, the pedestrian does not typically get run over. Instead, they get thrown over the bonnet and on the front windshield.

Modern crumple zones include a certain considuration to hitting a pedestrian. The bonnet is shaped in a more round fashion (in general, a round-shaped car is safer than a square-shaped car) and the head of the motor is placed a few good inches below the height of the hood itself, to allow making it softer. These modifications allow to make hitting a pedestrian at speeds of up to 20mph fairly soft and perfectly survivable, even without any serious injury. If you increase speeds to 40mph, however, the risk increased to a near 100% chance of mortality.
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