https://www.slashgear.com/2197980/how-airbags-deploy-so-quickly-in-a-crash-physics-explained/
Front airbags have been required in new passenger vehicles since the 1999 model year. While side airbags aren't specifically mandated, auto manufacturers install them to meet other federal safety requirements regarding side protection. The National Highway Traffic Safety Administration (NHTSA) claims that airbags saved over 70,000 lives in the U.S. since their implementation, so they work. But how do they work?
Airbags, which have recently become targets of theft, are part of the vehicle's passive safety system designed to help keep passengers safe during an accident. On average, an accident happens in roughly 200 milliseconds — less than 1/5 of a second. So, the system needs to detect, react, and deploy faster than that to be effective — usually just 10 to 30 milliseconds, which is quicker than you can blink. The deployment of an airbag has been described as "engineered violence" because it essentially contains and directs a literal explosion.
First of all, the term "airbag" isn't accurate since they don't actually use "air" per se. Today's systems use guanidinium nitrate with a copper nitrate oxidizer to produce nitrogen gas. When guanidinium nitrate is ignited, it breaks down into nitrogen gas, water, and carbon. The copper nitrate oxidizer is included to help reduce the temperature of the expelled gas. Older airbag systems once used ammonium nitrate, a chemical that didn't play nicely with humidity and moisture, and ended up causing several injuries and even some deaths. Guanidinium nitrate isn't affected by moisture.
Airbags are designed to deploy at various speeds depending on the scenario. If a car hits something narrow (think tree or pole), bags can deploy at just 8 mph. Impacts involving larger objects (such as other cars) can cause bags to unfurl at 18 mph. But the technology and methods used in the front passenger compartment are different than those used in other parts of the car.
Front airbags use small electronic accelerometers that can detect when a car suddenly decelerates, which is technically what occurs when it's involved in a crash. Using a technology called MEMS (micro-electro-mechanical systems), the onboard impact sensors determine — in the proverbial blink of an eye — changes in the vehicle's speed, how fast the car was going, what hit it, and whether the occupants were wearing seat belts. Passengers wearing seatbelts are considered safer, so airbags won't deploy unless the speed exceeds 16 mph. However, those not wearing them are at greater risk, so the system typically triggers bag deployment at speeds between 10 and 12 mph.
Side airbags are a bit different because they have much less space to work with. Whereas impacts from the front or back must first crumple through either the engine compartment or the trunk area, there's far less space an incoming vehicle or obstacle needs to go through when coming in from the sides. They do use accelerometers mounted inside the door, but they also use pressure-based sensors that measure how far and how fast the door deforms as it's hit.
In rollovers, additional sensors detect side-to-side motion and tilt to determine whether the vehicle is about to tip. Side curtain airbags, using compressed helium (or argon) or a combination of chemical propellants and compressed gas, inflate within 20 milliseconds and remain inflated longer than standard front airbags. Still, all these sensor detections culminate in the explosive "engineered violence" we mentioned earlier.
Once the circuit is activated, an electric current passes through a heating element, igniting the previously mentioned guanidinium nitrate. The resulting explosion releases nitrogen gas (not air) into the nylon bag, which is coated with talcum powder to prevent it from knotting up as it inflates. As it expands, it blows off the plastic cover that was keeping it out of view. All of this happens in as little as 10 milliseconds. Yes, cars can still be driven with blown airbags, but they really shouldn't be.
Between 1990 and 2008, the NHTSA believes that frontal airbag inflation during low-speed crashes caused over 290 deaths. Of those, almost 90% involved cars made before 1998; over 90% were children and infants, and over 80% of the occupants were either not wearing seat belts or not properly restrained. Today, serious injuries caused by airbag deployment are far less frequent than they used to be. And thanks to changes in federal requirements and technological advancements, faulty airbags and recalls have also declined. The NHTSA has a database where you can check to make sure there's nothing wrong with your vehicle's airbag system.
(Score: 2) by SDRefugee on Sunday June 28, @05:50PM (7 children)
You haven't LIVED until you have an airbag detonate in your face. Kinda like being slapped in the face and it DOES leave a temporary mark. Of course its far better than being dead..
America should be proud of Edward Snowden, the hero, whether they know it or not..
(Score: 5, Informative) by Unixnut on Sunday June 28, @06:08PM (6 children)
Up to a point... I remember when I was involved in an accident the first thing the doctors at the hospital asked me was whether the air bag went off, when I said the car didn't have an airbag they all breathed a sigh of relief, which surprised me so I asked why.
Turns out while airbags can increase the chances of saving your life in a small minority of serious accidents, in the larger majority of medium accidents (small accidents generally don't trigger the airbag) the airbag going off does more much damage to you than the accident itself would have.
It seems statistically airbags reduce "fatalities" in serious accidents so are seen as a good thing, despite apparently causing more damage to you in the vast majority of accidents you are likely to be involved in. Whether this is a worthwhile trade off depends on the person you ask.
(Score: 3, Interesting) by crm114 on Sunday June 28, @11:46PM (1 child)
Thanks for that ancedontal data point. Almost every time I've seen a crash where the airbags deployed... I thought to myself "If I was wearing my seatbelt, what's the problem?"
There are the "hit by a truck, flipped over, down the embankement, etc... cases." I got that. But most of the deployments I have seen are the vehicle frame, engine firewall, and 3 point seat-belts would have done just fine.
(Score: 4, Interesting) by Unixnut on Monday June 29, @12:29PM
Well, as I found out the primary purpose of airbags is to prevent you being killed in the most serious of accidents. Of course you may just end up a quadriplegic instead (again a personal choice which is better) but airbags reduce the "road fatalities" metric which is the only metric people seem to target when it comes to car safety.
Wearing a seatbelt is probably the most effective thing to reduce injuries in small/medium accidents, just by not having your face smash into the steering wheel or fly out through the windscreen.
The only place that is apparently not true is when you are driving on mountain roads, where I've been told it is better to not wear a seatbelt because the most common accident is rolling off the side down the mountain, in which case you want to jump (or be flung) out the car as soon as possible before it picks up speed on its way down. Supposedly this is why Italian cars never had the seatbelt-nanny warning (until the EU mandated it for every car).
Of course having an airbag go off if you are not wearing a seatbelt is the worst that can happen, because your head is approaching the steering wheel at speed while an explosive charge blasts in your face has a high chance of breaking your neck.
(Score: 2, Interesting) by Anonymous Coward on Monday June 29, @02:18AM (3 children)
> ... when I said the car didn't have an airbag they all breathed a sigh of relief,
Was this first generation airbags (all full power) or 2nd gen, which have (iirc) two charges and can blow either the small or large charge...or both for highest g accidents. They may also change power level depending on the occupant weight (using deflection of the seat springs for a scale).
If I'm explaining this wrong, please correct me, but that's what I remember when I chose to avoid buying cars from the 1990s that all had 1st gen airbags. I made my 1992 car (no airbag) last until I bought a 2002 with the 2nd gen airbags.
The change over to 2nd gen took several years as the models rolled over and were re-engineered, it was around year 2000.
(Score: 2) by Unixnut on Monday June 29, @08:39AM (2 children)
I really don't know much about airbag technology. My car didn't have an airbag but this accident happened around 2019, well past the 1990s so I presume the doctors were assuming a car from around 2019 themselves (they didn't ask for the cars age or other details about it except whether the air bag went off), in which case I guess that would be 2nd Generation airbag tech?
(Score: 0) by Anonymous Coward on Monday June 29, @12:42PM (1 child)
> well past the 1990s so I presume the doctors were assuming a car from around 2019 themselves
I'm more inclined to think that your doctors (unless they were very young) are still remembering airbag accidents from the 1st gen high power devices. I also suspect that an airbag injury is not something that a doctor would forget easily, unlike other sorts of car injuries. It's not widely known that the 2nd gen airbags were a better design.
While the 1st gen airbags were mostly phased out +/- year 2000, plenty of them were still on the road in the USA, in 2019, in older cars. These were bad news (too much explosive power) for low speed accidents and also for smaller/lighter people & children.
Maybe someone here on SN can find a study that looks at this?
(Score: 2) by Bentonite on Thursday July 02, @01:04AM
I suspects the doctors were told he crashed in an old car, thus they proceeded to investigate whether a 1st gen airbag was involved.
Due to how the 1st gen US airbags were designed based off unbelted crash tests, with the goal of keeping unbelted passengers alive, rather than let natural selection happen, such airbags inflate with significant force, which can cause significant injury if a passenger is too close to the wheel/dash and gets hit by the bag as it deploys (those smaller/lighter and without the strength to force themselves to the back into the seat, such as children tend to slide forward during pre-crash braking and the bag explodes into them - seatbelt pre-tensioners seem to somewhat mitigate that problem, but a loose fitting belt on a child would likely still have too much slack and a resulting slide forward - which is why children should be in the back, in a child seat until they're big enough to fit the seatbelt properly).
I suspect it's a case of confirmation bias of doctors not encountering cases of airbag deployment that didn't cause injury - only cases of airbag deployment that caused injury.
If you are in the back of the seat during a moderate speed collision, you won't get hit by the airbag and therefore it is unlikely for more than a minor injury to occur - as being gradually slowed down by the belt and then the airbag gradually dissipates the energy - therefore they don't end up in a hospital and therefore the collision isn't reported, or is reported as causing no injuries.
But due to the high collision rate on the roads, there are quite a few people that are forward in the seat and get hit by the airbag and a few who get eye irritation/asthma from the talcum powder/cornstarch and thus end up in the hospital with injuries or die, which makes it seem that airbags primarily causes damage in moderate speed collisions.
(Score: 3, Interesting) by VLM on Monday June 29, @01:46PM (1 child)
The primary purpose of airbags is to total the car in a minor accident to increase sales of new cars. If they pop, the car is written off and sent to the 3rd world at huge profit.
Its sold as they'll save your life, but usually marketed in situations where you'd be dead no matter what or have survived no matter what.
Follow the $$$$. And the $$$$ surely do not come from "saving lives" or whatever marketing nonsense used to push them.
(Score: 2) by Bentonite on Thursday July 02, @12:11AM
Non-defective airbags aren't triggered by low speed collisions and insurance companies are more glad to write cars off if the airbags aren't deployed (as more parts for sale means more profit), therefore it's not about increasing sales - there's plenty of defects in modern cars to ensure that.
A collision that is severe enough to trigger airbags is certainly not minor - the crumple zone is usually collapsed, or the frame is at least warped, or there is at least a significant dent in the undercarriage (if an object such as a lost tire strikes the undercarriage while the car is traveling at high speed, the result is significant deceleration temporarily, which is indistinguishable from a collision), which needs to be fixed to make the car safe to drive again - but as such repairs are no longer done at a reasonable price, it's more profitable for the insurance company to write the car off and sell it for parts, or to someone who will fix it for a reasonable price.
Airbags will most likely save you from significant injury during a moderate speed collision when combined with a seatbelt, as hitting a gas bag decelerates you slower than hitting a steering wheel or dashboard and will likely allow for significant injuries instead of death in high speed conditions.