Would you let your child put her feet out in front of her, and then have something slam into them at about 300 km/h? Of course you wouldn’t. So why do you let her ride with her feet up on the dash of your car?

Teens — and a surprising number of adults — think it’s cool to ride this way. But in the blink of an eye, the airbag could cause irreparable damage.

Every new car has at least two frontal airbags, in the centre of the steering wheel, and in the passenger side of the dash. In a frontal crash, these bags inflate with hot nitrogen gas within about 40 milliseconds. The bag is coming toward you at anywhere from 240 to 400 km/h.

And despite the fact that there’s the equivalent of a shotgun shell inside the dash, people still let their children ride this way, slouched in the seat with their feet up top.

If there’s a crash, and they’re lucky, they’ll only break their legs. If they aren’t, that bag will slam the thigh bones through the pelvis.

Airbags are a double-edged sword. They can prevent serious injury if you exercise caution around them, but they can also cause serious injury if you don’t.

Even state-of-the-art bags that inflate at a lower velocity when the system senses a smaller person in the seat still deploy with enough force to be dangerous or even deadly if you don’t respect them. Unlike in the movies, they don’t gently inflate and act as feather pillows.

In any seat, always sit up straight and wear your seatbelt. The airbag is designed in conjunction with the belt, which holds you in the proper position so the bag protects instead of injures you.

When driving, hold the wheel correctly. If you “hook” the wheel underhanded on a turn, holding it with your palm facing you, a deploying airbag will snap your wrist.

If you hold the wheel one-handed at the top, your rings and watch will be shot into your face. It’s safest to hold the wheel with both hands, at nine-and-three. Don’t curl your thumbs around the wheel, as they can be broken.