CAR AIR BAGS

Do you know how it really works?

What type of equation causes air bags to inflate?

  • Chemical Reactions to Generate the Gas to Fill an Airbag
    • Decomposition of Sodium Azide (NaN3)
    • Reactions to Remove Harmful Products
    • Reaction Stoichiometry


The first component of the airbag system is a sensor that can detect head-on collisions and immediately trigger the airbag's deployment. One of the simplest designs employed for the crash sensor is a steel ball that slides inside a smooth bore. Once the electrical circuit has been turned on by the sensor, a pellet of sodium azide (NaN3) is ignited. A rapid reaction occurs, generating nitrogen gas (N2). This gas fills a nylon or polyamide bag at a velocity of 150 to 250 miles per hour. This process, from the initial impact of the crash to full inflation of the airbags, takes only about 40 milliseconds.

What is the compound that creates the chemical reaction & what are the substances produced during the chemical reaction?

Inside the airbag is a gas generator containing a mixture of NaN3, KNO3, and SiO2. When the car undergoes a head-on collision, a series of three chemical reactions inside the gas generator produce gas (N2) to fill the airbag and convert NaN3, which is highly toxic. Sodium azide (NaN3) can decompose at 300oC to produce sodium metal (Na) and nitrogen gas (N2). The signal from the deceleration sensor ignites the gas-generator mixture by an electrical impulse, creating the high-temperature condition necessary for NaN3 to decompose. The nitrogen gas that is generated then fills the airbag. The purpose of the KNO3 and SiO2 is to remove the sodium metal by converting it to a harmless metal.
First, the sodium reacts with potassium nitrate (KNO3) to produce potassium oxide (K2O), sodium oxide (Na2O), and additional N2 gas. The N2 generated in this second reaction also fills the airbag, and the metal oxides react with silicon dioxide (SiO2) in a final reaction to produce silicate glass, which is harmless and stable. (First-period metal oxides, such as Na2O and K2O, are highly reactive, so it would be unsafe to allow them to be the end product of the airbag detonation.)




Gas molecules are constantly moving:

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Where does the energy source come from that starts the reaction?

When involved in a collision, trip sensors in cars send an electric signal to an ignitor. The heat generated by this causes sodium azide to decompose into sodium metal and nitrogen gas, which inflates the car's air bags.

What are some statistics on how air bags are beneficial?

Newton's familiar first law of motion says that objects moving at a constant velocity continue at the same velocity unless an external force acts upon them. This law, known as the law of inertia, is demonstrated in a car collision. When a car stops suddenly, as in a head-on collision, a body inside the car continues moving forward at the same velocity as the car was moving prior to the collision, because its inertial tendency is to continue moving at constant velocity. However, the body does not continue moving at the same velocity for long, but rather comes to a stop when it hits some object in the car, such as the steering wheel or dashboard. Thus, there is a force exerted on the body to change its velocity. Injuries from car accidents result when this force is very large. Airbags protect you by applying a restraining force to the body that is smaller than the force the body would experience if it hit the dashboard or steering wheel suddenly, and by spreading this force over a larger area.
-The National Highway Traffic Safety Administration (NHTSA) says that frontal airbags saved 2,213 lives in 2012. Airbags, combined with seatbelts, are the most effective safety protection available for passenger vehicles. Seatbelts alone reduce the risk of fatal injury to front-seat passenger car occupants by 45 percent.

-Virtually all new cars have air bags and they're saving lives. The fatality-reducing effectiveness for airbags is 14 percent when no seatbelt is used and 11 percent when a seatbelt is used in conjunction with airbags. Side airbags, which protect the head, chest and abdomen, reduce driver deaths by an estimated 37 percent, according to the Insurance Institute for Highway Safety.

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How does an airbag work
How an Airbag works