Thursday 26th February 2015
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We all know what a seat belt is don’t we? We all know that we are legally obliged to wear one because if we don’t we could get injured in the event of a collision. Here's what you need to know about how seat belts keep you safe and legal!

How do seat belts work?

Basically the seatbelt keeps you contained in your seat in the event of a sudden stop or collision. The seatbelt will stop your body being thrown through a windscreen or onto another occupant and injuring them and yourself.   In essence the seatbelt stops inertia from taking place.  Inertia is when an object keeps moving at the same pace unless something stops it.  Say you were driving along at 40 mph and then you had a crash the car would come to an abrupt halt but if you weren’t wearing a seatbelt you would either smash into the dashboard or crash through the windscreen at 40 mph.  Something has to slow you down and that is the seatbelt’s function. A seat belt has two parts, the lap belt which goes over the pelvis and the shoulder belt which goes across the chest. This means that the majority of the stopping force applies to the rib cage and pelvis which are pretty sturdy parts of the body and can take the force.

Many seatbelts have webbing bolted to the body of the car and this webbing is connected to a retractor mechanism.  The main element of this mechanism is a spool which is attached to one end of the webbing and a spring inside the retractor allows the spool to rotate and wind up loose webbing.  If the webbing is pulled out the spool rotates anti clockwise thus turning the attached spring in a similar direction.  As a result the spring tightens up, rotates the spool clockwise and prevents any slack in the belt. When a collision occurs the retractor’s locking mechanism prevents the spool from rotating.  There are two types of locking systems.  One is triggered by movement from the car and locks the spool when impact hits the car. The other type is triggered by the belt’s movement and the spool locks when something sharply pulls the belt webbing.

Some newer seatbelts use a pretensioner mechanism which tightens the belt webbing. Its aim is to tighten up slack in the belt webbing when impact occurs. A pretensionser pulls in the belt whereas a traditional locking mechanism in a retractor prevents the belt from extending more. However, pretensioners work with the locking mechanisms and don’t replace them.  There are various pretensioner systems out there with some pulling the retractor mechanism backward and some rotating the spool itself.  Usually they are wired to the same system (central control processor) that activates the vehicle’s air bags.  So when an impact is identified the processor starts the pretensioner and then the air bag.

Make sure you put it on and put it on right

Seat belts can injure as well as protect

The faster your speed when driving and on impact the harder the seatbelt will press on you and is likely to cause you injuries.  If you don’t wear the seat belt properly, either too high, too low, too loose or  too tight, that can also contribute towards the seat belt causing injuries.  Damage to the chest, ribs, shoulder, soft tissues and internal organs have been reported because of seat belts.  Many common injuries include fractures and bruising such as cracked sternums, bruised shoulders and cracked ribs.  Broken ribs can damage internal organs which can prove to be far more deadly. It is easy to assign blame to the seatbelts as the injuries occur where seat belts are worn. Some seat belt systems use load limiters to minimize injuries from belts by releasing a bit more excess belt webbing when huge force is applied to the belt.

However, ultimately it is much safer to wear seat belts and they must be worn properly. As you pull the shoulder strap across you ensure that it goes over your collarbone and chest, never rubbing on your face or neck. Make sure that the lower belt fits snuggly over your lap and pelvis, never on your stomach. Pregnant ladies should place the lower belt under their stomach and not on or above it.

The law and seat belts

Remember that if your vehicle is fitted with seat belts you must wear one. Only one person per seat is allowed so that every occupant has the use of a seat belt.  Children must use the appropriate car seat for their weight until they turn 12 or reach 135 cm tall.

The only exceptions for not wearing a seatbelt are:

  • A driver reversing a vehicle
  • Supervising a learner drive while they reverse
  • Occupants in fire, police and rescue service vehicles
  • Occupants in trade vehicles who are investigating faults
  • Licenses taxi drivers who are carrying or looking for customers
  • Drivers of good vehicles who are delivering and travelling not more than 50 metres between stops

On the spot fines of £100 can be dished out if you don’t wear a seat belt. If prosecuted a fine of up to £500 can be levied.  Other than the above mentioned scenarios the only other exemptions would be on medical grounds.  In this case the doctor must give you a ‘Certificate of Exemption from Compulsory Seat Belt Wearing’ and you must keep the certificate in your vehicle, inform your car insurer and show the certificate to police if you are stopped.   Pregnant and disabled people must wear seat belts unless they have permission from their doctors.

The only other exemption would be for classic cars which apply only if the car was originally made without seat belts.  There are some rules about carrying children in these cars which you should be aware of if you have a classic car.

Did you know that if you don’t wear a seat belt you are twice as likely to die as if you did wear one? It isn’t any co-incidence that drivers and passengers aged 17 to 34 have the highest accident rate and the lowest seat belt wearing rates!

If you want to get an idea of what can happen if you don’t wear a seatbelt, visit Think’s website and see their crash simulation based on not wearing a seatbelt:

So be safe and on the right side of the law and belt up!  If you need seat belts or restraints or extenders for your seat belts contact us now.