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.
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Image: NEW CAR ASSESSMENT PROGRAM, CRASH TEST AREA
CRASHES trip sensors in cars that send an electric signal to an ignitor. The heat generated causes sodium azide to decompose into sodium metal and nitrogen gas, which inflates the car's air bags.
Under normal circ*mstances, 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.
What prompts an air bag to inflate by way of this reaction? There are sensors in the front of the automobile that detect a collision. These sensors send an electric signal to the canister that contains the sodium azide and the electric signal detonates a small amount of an igniter compound. The heat from this ignition starts the decomposition of the sodium azide and the generation of nitrogen gas to fill the air bag. What is particularly amazing is that from the time the sensor detects the collision to the time the air bag is fully inflated is only 30 milliseconds, or 0.03 second. Some 50 milliseconds after an accident, the car's occupant hits the air bag and its deflation absorbs the forward-moving energy of the occupant.
Air bags inflate when a sensor detects a front-end crash severe enough to trigger their deployment. The sensor sends an electric signal to start a chemical reaction that inflates the air bag with harmless nitrogen gas. All this happens faster than the blink of an eye.
The inflator starts a chemical reaction that results in an explosion of nitrogen gas. The airbag gets filled by the gas. When the airbag is fully filled with nitrogen, it ruptures through the panel that is holding it and cushions the passenger.
Newer airbags have a safety belt sensor and use an algorithm to decide whether to deploy the bag in a given crash, depending on whether people are using safety belts. For unbelted occupants, a front airbag will typically deploy when the crash is the equivalent of an impact into a rigid wall at 10-12 mph.
Your airbags should also deploy if you accidentally rear-end another driver at a certain speed. However, if you were hit from behind or on the side by another vehicle, or if a collision causes your vehicle to roll over, your airbag sensors most likely won't be triggered.
The name "airbag" can be deceiving because the bag is not exactly filled with air. Instead, this life-saving device is filled with nitrogen gas, which is produced in a swift reaction by a compound known as sodium azide.
However, most airbags are programmed to deploy at different speeds depending on whether the occupants are belted or unbelted. For unbelted occupants, the airbag has a low-speed deployment, usually at speeds of around 10-12 miles per hour. For belted occupants, airbags deploy at speeds of 15-17 miles per hour.
Air bags do not deploy in the billowing cloud-like manner as seen in certain television advertisem*nts. As mentioned above, air bags explode at speeds of 200 MPH for 12 to 18 inches. This is a violent reaction, necessary to have the bag deployed and beginning to slowly deflate when the occupant contacts the bag.
Frontal air bags are generally designed to deploy in "moderate to severe" frontal or near-frontal crashes, which are defined as crashes that are equivalent to hitting a solid, fixed barrier at 8 to 14 mph or higher. (This would be equivalent to striking a parked car of similar size at about 16 to 28 mph or higher.)
There is no law preventing you from driving your car after airbags deploy, but this is not advisable. It is important for your safety to have your car checked for damage and your airbags replaced by an authorized service technician before driving the vehicle.
Because airbags have small explosives in them that allow them to protect with a bang, they will often emit a smoky smell and can seem like there's a fire. However, it's important to know that airbags don't catch on fire without other areas of the car being on fire, first.
Neck and Spine Injuries: The force of airbag deployment can lead to whiplash, where the neck is suddenly jerked back and forth. More severe cases might involve spinal fractures or other related traumas to the cervical spine, especially if you weren't wearing a seatbelt.
Generally, frontal and near-frontal collisions at moderate to high speeds will trigger the airbag system. If the accident involves a side impact, rear-end collision, or a low-speed bump, the airbags may not deploy because they might not be effective or necessary to prevent injury in these situations.
However, the airbags provided in the car are useless if the occupants are not wearing their seatbelts. In order to make the car occupants safe, the seatbelts and airbags work together, and having one without the other significantly decreases the safety of occupants in case of a crash.
A huge amount of nitrogen gas immediately rushes out with an explosion and fills the airbag. It is amazing that from the time the sensor detects the collision to the time the airbag is fully inflated is only 30 milliseconds, or three one-hundredths of a second!
The speed at which an airbag deploys in a car crash can vary depending on the severity of the collision. Generally, airbags are designed to deploy when the vehicle experiences a significant impact, typically around 8 to 14 miles per hour (13 to 23 kilometers per hour) or faster.
The answer would be found in a fascinating chemical called sodium azide, NaN3. When this substance is ignited by a spark it releases nitrogen gas which can instantly inflate an airbag.
With airbags now standard equipment on cars, it's easy to take them for granted. You shouldn't. Popping out at up to 200 mph, front airbags can fully inflate in 1/20 of a second—literally faster than a blink of an eye.
The airbag module contains both an inflator unit and the lightweight fabric airbag. The airbag system consists of three basic parts: (1) An airbag module, (2) crash sensors, and (3) a diagnostic unit. Some systems may also have an on/off switch, which allows the airbag to be deactivated.
In a seat belt pre-tensioner, this hot gas is used to drive a piston that pulls the slack out of the seat belt. In an airbag, the initiator is used to ignite solid propellant inside the airbag inflator. The burning propellant generates inert gas which rapidly inflates the airbag in approximately 20 to 30 milliseconds.
Introduction: My name is Lidia Grady, I am a thankful, fine, glamorous, lucky, lively, pleasant, shiny person who loves writing and wants to share my knowledge and understanding with you.
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