Safety cell

The safety cell is a safety feature in modern cars developed in 1951 by Mercedes-Benz. It's considered a critical innovation in car safety as it protects all the occupants in an event of a crash. Many carmakers such as Renault, Toyota, Honda, Volkswagen, Fiat, Volvo, Subaru and Mercedes-Benz use the safety cell for their cars.

Functions
The safety cell has two crumple zones at both ends and a 'cage' in the occupant compartment. In a crash, the front end is crushed absorbing much of the inertial energy as it can. The same applies to the rear end. As the crumple zones absorb energy by crushing, it helps the car slow down the impact(reducing the decelleration time). The result to the occupants is reduced whiplash injury. Also, crush injuries can be reduced because of the strength of the cage.

However, the safety cell has to be strong enough to sustain an impact. Many safety cells use high-strength steel. Another thing about crumple zones are that the engine and gearbox have to be breakable. That helps make the front crumple zone do the better job of absorbing energy and it also helps that on impact, the steering column should collapse to prevent life threatening chest injuries to the driver. There are other safety cells that not only absorb crash energy, they disperse energy away from the crashing car. Many small cars use this concept.

Comparison with a car without a safety cell
Let's say we take two equivalently sized cars. One with a safety cell and one without. We then crash test them under the same conditions for both cars. After they've been crashed, we see the difference.

With safety cell
We can see that in a crash, the front crumple zone has been shortened by half the orginal length. That's good because the crumple zone has absorbed the impact reducing the deceleration time. The bumper, headlights and the wheels gave way for the impact and not only these parts, the engine, gearbox and other components inside the engine bay also gave way esnuring the crumple zone to do its job.

When you look at the cabin, you don't see much and you resume that the cabin is all good. In the inside of the cabin, everything's okay and the crash test dummies look perfectly fine. This comes to show that if there are real people, they would be able to survive the crash. Best still when you look in the cabin again, there's space for the dummies' legs, space between the steering wheel and the dummie's chest and space everywhere around the crash test dummies. That's good because the dummies are safe from crush injuries and although they might show a slight risk of injuries, luckily, the injuries won't be enough to kill you.

Without safety cell
Now, let's look at the car without a safety cell after the crash. The whole front has been crumpled and we assure that the crumple zone has done its job. But if you look at the cabin, there is a definite difference. The cabin has been deformed and crushed along with the crumple zone. You can see that the crash test dummies have lost a deal of space as the cabin crumpled. The dummies' legs are more prone to serious injuries when they've been pushed towards the dashboard and there's an increased risk of life-threatening chest injuries particularly for the driver as it hits the steering wheel whilst the airbag is fired up.

So now you know how important it is for a car to have a safety cell.