Question

Scientific question: How does the choice of chemical ingredient in airbags influence their effectiveness.

How Airbags Work Let’s call it “engineered violence.” Airbags may seem soft and cuddly as long as they’re packed away in your steering wheel, dashboard, seats, or pillars, but what makes them work is their ability to counteract the violence of a collision with a structured sort of violence of their own. Every airbag deployment is literally a contained and directed explosion.



“We don’t like to use the word ‘explosion’ around here,” claims Ken Zawisa, the global airbag engineering specialist responsible for frontal airbag strategies at GM. “But it is a very fast, well-controlled chemical reaction. And heat and gas are the result.” The term “airbag” itself is misleading since there’s no significant “air” in these cushions. They are, instead, shaped and vented nylon-fabric pillows that fill, when deployed, with nitrogen gas. They are designed to supplement seatbelt restraints and help distribute the load exerted on a human body during an accident to minimize the deceleration rate and likelihood of injury. But while “supplement the seatbelt” is the mission of airbags, federal regulations require that they be tested and made effective for unbelted occupants, vastly complicating their task. Airbags must do their work quickly because the window of opportunity—the time between a car’s collision into an object and an occupant’s impact into the steering wheel or instrument panel—lasts only milliseconds. For illustration’s sake, imagine a Corvette hitting a bridge abutment head-on at 30 mph. The clock starts the instant the tip of the car’s nose hits concrete. The Mechanics There are six main parts of an airbag system: an accelerometer; a circuit; a heating element; an explosive charge; and the bag itself.



The accelerometer keeps track of how quickly the speed of your vehicle is changing. When your car hits another car—or wall or telephone pole or deer—the accelerometer triggers the circuit. The circuit then sends an electrical current through the heating element, which is kind of like the ones in your toaster, except it heats up a whole lot quicker. This ignites the charge which prompts a decomposition reaction that fills the deflated nylon airbag (packed in your steering column, dashboard or car door) at about 200 miles per hour. The whole process takes a mere 1/25 of a second. The bag itself has tiny holes that begin releasing the gas as soon as it’s filled. The goal is for the bag to be deflating by time your head hits it. That way it absorbs the impact, rather than your head bouncing back off the fully inflated airbag and causing you the sort of whiplash that could break your neck. Sometimes a puff of white powder comes out of the bag. That’s cornstarch or talcum powder to keep the bag supple while it’s in storage. (Just like a rubberband that dries out and cracks with age, airbags can do the same thing.) Most airbags today have silicone coatings, which makes this unnecessary. Advanced airbags are multistage devices capable of adjusting inflation speed and pressure according to the size of the occupant requiring protection. Those determinations are made from information provided by seat-position and occupant-mass sensors. The SDM also knows whether a belt or child restraint is in use.



Today, manufacturers want to make sure that what’s occurring is in fact an accident and not, say, an impact with a pothole or a curb. Accidental airbag deployments would, after all, attract trial lawyers in wholesale lots. So if you want to know exactly what the deployment algorithm stored in the SDM is, just do what GM has done: Crash thousands of cars and study thousands of accidents. The Detonation: Decomposition Reactions Manufacturers use different chemical stews to fill their airbags. A solid chemical mix is held in what is basically a small tray within the steering column. When the mechanism is triggered, an electric charge heats up a small filament to ignite the chemicals and—BLAMMO!—a rapid reaction produces a lot of nitrogen gas. Think of it as supersonic Jiffy Pop, with the kernels as the propellant. This type of chemical reaction is called “decomposition”. A decomposition reaction is a reaction in which a compound breaks down into two or more simpler substances. A reaction is also considered to be decomposition even when one or more of the products are still compounds.



This is what you're answering not the scientific question: Use the scientific question and the reading above to inform the reader of the goals related to to the airbag experiment.

Answer 1

The choice of chemical ingredients in airbags influences their effectiveness in several key ways:

1. Rate and speed of gas generation. The chemicals must decompose rapidly enough to fill the airbag before the occupant impacts the steering wheel or dashboard. Slower reactions will not produce enough gas quickly enough. Faster reactions can lead to over-pressurization and airbag rupture.

2. Total volume of gas produced. The ingredients must generate enough gas to rapidly inflate the airbag to an adequate size. Not enough gas will result in an under-inflated bag that does not properly cushion the occupant.

3. Controlled deflation. The airbag must deflate in a controlled manner as the occupant moves into it. Chemicals that produce gas too quickly can lead to an over-inflated bag that does not absorb impact energy effectively. The ingredient proportion and composition can influence how quickly the bag deflates.

4. Modulation for different impacts. More advanced airbags use sensors to determine the severity of impact and size of the occupant. The chemical system must be able to modulate deployment accordingly by speeding up, slowing down, or terminating gas generation at the appropriate times. This helps prevent unnecessary airbag deployment or inadequate cushioning for different event scenarios.

5. Stability and safety. The chemical ingredients must remain stable and non-hazardous until deployed. They cannot be overly volatile, corrosive or reactive prior to collision. Proper encapsulation and housing of the chemicals is also required to avoid leaks that could activate the airbag inadvertently or lead to harm from exposure.

In summary, the choice of airbag chemicals involves balancing these different and sometimes competing goals to achieve rapid, controlled and modulated deployments that properly cushion occupants while also ensuring stability, safety and avoiding unnecessary airbag operations. The ingredients, proportions and overall system design must all be optimized to meet the complex requirements for effective airbag performance.