What is an airbag, how does it
work and why do we need it ?
Let’s find out what exactly is an airbag, why is it
essential and the working mechanism of an airbag.
The airbag system is one of the most important parts
of your vehicle's safety components. Proper airbag deployment can ensure that
you and your passengers survive a crash that you may have otherwise experienced
serious injury or death as a result of. When an accident occurs, airbags
inflate faster than you can blink your eye. Airbags are key components in
automotive safety systems, and, although we cannot see them perform under
normal conditions with the naked eye, they soften the impact of collisions by
keeping passengers from contacting the steering wheel, dashboard, front glass,
and other parts of the automobile. Airbag deployment has saved thousands of
lives through the years.
What
Are Airbags?
Airbags are
stretchable fabrics or other materials that are tightly packed in various
locations throughout your vehicle. There are airbags at the front of the
dashboard in most cars, and many vehicles have airbags along the side of the car
as well. These bags are compressed and kept in a small area. When there is an
accident, the airbags fill up with air very quickly to provide a cushioning
system for the people in the car so that they are not thrown around in the
event of a crash. While this does not necessarily prevent total injury or
death, it can be very helpful in cushioning the passengers in a car in many
cases.
Although we don't usually associate automobiles with
chemistry, a lot of chemistry takes place in a working car--the burning of
gasoline to run the engine, for example, and chemical reactions in the battery
to generate electricity. Another reaction--one that most drivers would just as
soon not experience firsthand--involves the air bag. Air bags are not inflated
from some compressed gas source but rather from the products of a chemical
reaction. The chemical at the heart of the air bag reaction is called sodium
azide, or NaN3.
CRASHES trip sensors in cars that send an electric
signal to an inflator. The heat generated causes sodium azide to decompose into
sodium metal and nitrogen gas, which inflates the car's air bags.
Under normal circumstances, this molecule is quite
stable. If heated, though, it will fall apart. The chemical equation 2 NaN3
--> 2 Na + 3 N2 describes exactly how it falls apart. Notice that the second
product of the above reaction is N2, also known as nitrogen gas. A handful (130
grams) of sodium azide will produce 67 liters of nitrogen gas--which is enough
to inflate a normal air bag 0.03 SECOND is all it takes to inflate an air
bag.
That's not the only chemistry involved. Notice that
the other chemical into which sodium azide falls apart is Na, or sodium. Sodium
is a very reactive metal that will react rapidly with water to form sodium
hydroxide; as a result, it would be quite harmful if it got into your eyes,
nose or mouth. So to minimize the danger of exposure, air bag manufacturers mix
the sodium azide with other chemicals that will react with the sodium and, in
turn, make less toxic compounds.
The most
important parts of the success of the airbag system are the crash sensors.
These small pieces of electronics are designed to tell when the vehicle has
been damaged in an accident. They respond to several different sets of stimuli,
including sudden stopping, increased pressure as pieces of the car are moved
due to the force of the collision, and more.
Different types of sensors measuring wheel speed,
seat occupant status, brake pressure and impact, and other vehicle status
indicators are monitored by the airbag control unit located in the front
portion of the cabin. The sensors relay signals to the airbag control unit,
which analyzes the data and can orchestrate safety features like seat belt
lock, automatic door locks, as well as airbag deployment.
Two types of airbag
sensors used in cars are electrical and mechanical. Electrical sensors vary in
design. Some use an electromechanical "ball and tube" mechanism,
which basically consists of a small tube containing a circuit switch and ball
that's held together by a small magnet. If a collision occurs, the ball is
dislodged from the magnet and rolls forward in the tube, hitting a switch that
completes the electrical circuit. Other electrical designs are similar in
principle, using a metal roller or spring loaded weight instead of a ball, or
in newer cars, an accelerometer to trip the sensor. Mechanical sensors work
independent of the electrical system and respond similarly to the electrical
sensors, with a design that actuates a firing pin triggering a small explosion
after a crash. Since a mechanical sensor does not require a power source, it
cannot be deactivated like an electrical sensor can when the battery is
disconnected.
The success of the airbag system relies upon the
crash sensors working not only accurately but also extremely quickly, so the
most expensive and technologically advanced part of the airbag system are here.
Inflator
Once the
control unit determines there is an accident, it sends a signal to the inflator
system. The inflator sets off a chemical charge, producing an explosion of
nitrogen gas, filling up the airbag. As the airbag fills up, it bursts through
the paneling that contains it and enters into the space of the car in order to
protect you.
This all happens in an instant, usually within 25 or
50 milliseconds. That translates to almost 200 miles per hour. The airbag then
will deflate itself on its own once it deploys.
If you want to check out the video on how airbags
work click the link
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