Airbags

[Franco Cozzo]

Just wondering, with airbags and how they deploy when you have an accident, wouldn't what ever inflates the bag cause 3rd degree burns to your hands/arms? I'd imagine what ever makes the bag fill up would be pretty hot.

[Melz]

I've heard of burns, broken arms, etc.

But at the end of the day I'd prefer a broken arm to brain damage or even death!

[Fev]

There are sensors in the bumpers usually like a switch. When an impact occurs that is strong enough to make the two contacts in the switch complete a circuit it sets off the airbags.

The airbags are inflated with a compressed gas, and as with most gasses it becomes very cold when it's compressed which i imagine reverses the heat caused by the friction of the gas expanding so fast inside the airbag.

Thats my theory on how it works anyway.

[The Monty]

Yes thats correct, and thats why airbags wont go off unless it will stop more damage then it causes. For instance, little tail ender where you get a sore neck from the impact, it wont go off for that. Hit a truck, it will go off.

[auxr]

wikipedia - a vast information file that sometimes contains some valuable information that someone may be wanting an answer to - XCPWSF, happy reading :

How airbags work

The design is conceptually simple; a central "Airbag control unit" (ACU) (a specific type of ECU) monitors a number of related sensors within the vehicle, including accelerometers, impact sensors, side (door) pressure sensors, wheel speed sensors, gyroscopes, brake pressure sensors, and seat occupancy sensors. When the requisite 'threshold' has been reached or exceeded, the airbag control unit will trigger the ignition of a gas generator propellant to rapidly inflate a nylon fabric bag. As the vehicle occupant collides with and squeezes the bag, the gas escapes in a controlled manner through small vent holes. The airbag's volume and the size of the vents in the bag are tailored to each vehicle type, to spread out the deceleration of (and thus force experienced by) the occupant over time and over the occupant's body, compared to a seat belt alone.

The signals from the various sensors are fed into the Airbag control unit, which determines from them the angle of impact, the severity, or force of the crash, along with other variables. Depending on the result of these calculations, the ACU may also deploy various additional restraint devices, such as seat belt pre-tensioners, and/or airbags (including frontal bags for driver and front passenger, along with seat-mounted side bags, and "curtain" airbags which cover the side glass). Each restraint device is typically activated with one or more pyrotechnic devices, commonly called an initiator or electric match. The electric match, which consists of an electrical conductor wrapped in a combustible material, activates with a current pulse between 1 to 3 amperes in less than 2 milliseconds. When the conductor becomes hot enough, it ignites the combustible material, which initiates the gas generator. 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. An airbag must inflate quickly in order to be fully inflated by the time the forward-traveling occupant reaches its outer surface. Typically, the decision to deploy an airbag in a frontal crash is made within 15 to 30 milliseconds after the onset of the crash, and both the driver and passenger airbags are fully inflated within approximately 60-80 milliseconds after the first moment of vehicle contact. If an airbag deploys too late or too slowly, the risk of occupant injury from contact with the inflating airbag may increase. Since more distance typically exists between the passenger and the instrument panel, the passenger airbag is larger and requires more gas to fill it.

Front airbags normally do not protect the occupants during side, rear, or rollover accidents. Since airbags deploy only once and deflate quickly after the initial impact, they will not be beneficial during a subsequent collision. Safety belts help reduce the risk of injury in many types of crashes. They help to properly position occupants to maximize the airbag's benefits and they help restrain occupants during the initial and any following collisions.

In vehicles equipped with a rollover sensing system, accelerometers and gyroscopes are used to sense the onset of a rollover event. If a rollover event is determined to be imminent, side-curtain airbags are deployed to help protect the occupant from contact with the side of the vehicle interior, and also to help prevent occupant ejection as the vehicle rolls over.

Triggering conditions
Airbags are designed to deploy in frontal and near-frontal collisions more severe than a threshold defined by the regulations governing vehicle construction in whatever particular market the vehicle is intended for. U.S. regulations require deployment in crashes at least equivalent in deceleration to a 23 km/h(14 mph) barrier collision, or similarly, striking a parked car of similar size across the full front of each vehicle at about twice the speed. International regulations are performance based, rather than technology-based, so airbag deployment threshold is a function of overall vehicle design.

Unlike crash tests into barriers, real-world crashes typically occur at angles other than directly into the front of the vehicle, and the crash forces usually are not evenly distributed across the front of the vehicle. Consequently, the relative speed between a striking and struck vehicle required to deploy the airbag in a real-world crash can be much higher than an equivalent barrier crash. Because airbag sensors measure deceleration, vehicle speed and damage are not good indicators of whether an airbag should have deployed. Airbags can deploy due to the vehicle's undercarriage striking a low object protruding above the roadway due to the resulting deceleration.

The airbag sensor is a MEMS accelerometer, which is a small integrated circuit with integrated micro mechanical elements. The microscopic mechanical element moves in response to rapid deceleration, and this motion causes a change in capacitance, which is detected by the electronics on the chip that then sends a signal to fire the airbag. The most common MEMS accelerometer in use is the ADXL-50 by Analog Devices, but there are other MEMS manufacturers as well.

Initial attempts using mercury switches did not work well. Before MEMS, the primary system used to deploy airbags was called a "rolamite". A rolamite is a mechanical device, consisting of a roller suspended within a tensioned band. As a result of the particular geometry and material properties used, the roller is free to translate with little friction or hysteresis. This device was developed at Sandia National Laboratories. The rolamite, and similar macro-mechanical devices were used in airbags until the mid-1990s when they were universally replaced with MEMS.

Nearly all airbags are designed to automatically deploy in the event of a vehicle fire when temperatures reach 150-200 °C (300-400 °F). This safety feature, often termed auto-ignition, helps to ensure that such temperatures do not cause an explosion of the entire airbag module.

Today, airbag triggering algorithms are becoming much more complex. They try to reduce unnecessary deployments (for example, at low speed, no shocks should trigger the airbag, to help reduce damage to the car interior in conditions where the seat belt would be an adequate safety device), and to adapt the deployment speed to the crash conditions. The algorithms are considered valuable intellectual property. Experimental algorithms may take into account such factors as the weight of the occupant, the seat location, seatbelt use, and even attempt to determine if a baby seat is present.

Inflation
When the frontal airbags are to deploy, a signal is sent to the inflator unit within the airbag control unit. An igniter starts a rapid chemical reaction generating primarily nitrogen gas (N2) to fill the airbag making it deploy through the module cover. Some airbag technologies use compressed nitrogen or argon gas with a pyrotechnic operated valve ("hybrid gas generator"), while other technologies use various energetic propellants. Propellants containing the highly toxic sodium azide (NaN3) were common in early inflator designs. However, propellants containing sodium azide were widely phased out during the 1990s in pursuit of more efficient, less expensive and less toxic alternatives.[citation needed]

The azide-containing pyrotechnic gas generators contain a substantial amount of the propellant. The driver-side airbag would contain a canister containing about 50 grams of sodium azide. The passenger side container holds about 200 grams of sodium azide. The incomplete combustion of the charge due to rapid cooling leads to production of carbon monoxide (CO) and nitrogen(II) oxide as reaction by-products.[30]

The alternative propellants may incorporate, for example, a combination of nitroguanidine, phase-stabilized ammonium nitrate (NH4NO3) or other nonmetallic oxidizer, and a nitrogen-rich fuel different than azide (eg. tetrazoles, triazoles, and their salts). The burn rate modifiers in the mixture may be an alkaline metal nitrate (NO3-) or nitrite (NO2-), dicyanamide or its salts, sodium borohydride (NaBH4), etc. The coolants and slag formers may be eg. clay, silica, alumina, glass, etc. Other alternatives are eg. nitrocellulose based propellants (which have high gas yield but bad storage stability, and their oxygen balance requires secondary oxidation of the reaction products to avoid buildup of carbon monoxide), or high-oxygen nitrogen-free organic compounds with inorganic oxidizers (e.g., di or tricarboxylic acids with chlorates (ClO3-) or perchlorates (HClO4) and eventually metallic oxides; the nitrogen-free formulation avoids formation of toxic nitrogen oxides).

From the onset of the crash, the entire deployment and inflation process is about 0.04 seconds — faster than the blink of an eye (about 0.2 seconds). Because vehicles change speed so quickly in a crash, airbags must inflate rapidly to reduce the risk of the occupant hitting the vehicle's interior.

Variable-force deployment
Advanced airbag technologies are being developed to tailor airbag deployment to the severity of the crash, the size and posture of the vehicle occupant, belt usage, and how close that person is to the actual airbag. Many of these systems use multi-stage inflators that deploy less forcefully in stages in moderate crashes than in very severe crashes. Occupant sensing devices let the airbag control unit know if someone is occupying a seat adjacent to an airbag, the mass/weight of the person, whether a seat belt or child restraint is being used, and whether the person is forward in the seat and close to the airbag. Based on this information and crash severity information, the airbag is deployed at either a high force level, a less forceful level, or not at all.

Adaptive airbag systems may utilize multi-stage airbags to adjust the pressure within the airbag. The greater the pressure within the airbag, the more force the airbag will exert on the occupants as they come in contact with it. These adjustments allow the system to deploy the airbag with a moderate force for most collisions; reserving the maximum force airbag only for the severest of collisions. Additional sensors to determine the location, weight or relative size of the occupants may also be used. Information regarding the occupants and the severity of the crash are used by the airbag control unit, to determine whether airbags should be suppressed or deployed, and if so, at various output levels.


Post-deployment view of a SEAT Ibiza airbag[edit] Post-deployment
Once an airbag deploys, deflation begins immediately as the gas escapes through vent(s) in the fabric (or, as it's sometimes called, the cushion) and cools. Deployment is frequently accompanied by the release of dust-like particles, and gases in the vehicle's interior (called effluent). Most of this dust consists of cornstarch, french chalk, or talcum powder, which are used to lubricate the airbag during deployment. Newer designs produce effluent primarily consisting of harmless talcum powder/cornstarch and nitrogen gas. In older designs using an azide-based propellant (usually NaN3), varying amounts of sodium hydroxide nearly always are initially present. In small amounts this chemical can cause minor irritation to the eyes and/or open wounds; however, with exposure to air, it quickly turns into sodium bicarbonate (baking soda). However, this transformation is not 100% complete, and invariably leaves residual amounts of hydroxide ion from NaOH. Depending on the type of airbag system, potassium chloride (often used as a table salt substitute) may also be present.

For most people, the only effect the dust may produce is some minor irritation of the throat and eyes. Generally, minor irritations only occur when the occupant remains in the vehicle for many minutes with the windows closed and no ventilation. However, some people with asthma may develop a potentially lethal asthmatic attack from inhaling the dust.

[Mr Hardware]

wouldn't what ever inflates the bag cause 3rd degree burns to your hands/arms?

Correct. We had a cabbie once was in a medium sized accident, had the airbag go off, burns up his arms. He was off work for a week or two. Apparently if he hadn't have had an airbag, he would have been fine and back at work the next day.

[deesun]

^^^^ Or it's possible he could have smashed his face on the steering wheel and been off work for 6 weeks or longer to have reconstructive surgery. Who really knows. What we really know is that they save lives just like seat belts which can also cause minor injuries but every evolution of the bag/belt deploys more progressive than the last reducing injuries even more.

[stevz]

Originally Posted by Fev

There are sensors in the bumpers usually like a switch. When an impact occurs that is strong enough to make the two contacts in the switch complete a circuit it sets off the airbags.

That is completely incorrect. In most cars the airbag sensor is a small module which measures decelleration, and is usually located inside the car.

[SVD]

http://inventors.about.com/od/astart...a/air_bags.htm
history of airbags and how/why they go off and what is used to get them out of the wheel etc...

[PANELCORP]

Most modern airbags are two stage and inflate to preset levels depending on the severity of an imapct

There is some great video on youtube from the crashlab here in Sydney that I recommend you watch if you are worried about the burns you (may) get

Here's what happens to old Commodores with 4ookg of ballast in the boot (remember how many times we've all carried pool salt back from the shops)

Follow the link:

http://www.youtube.com/watch?v=CgjtSilW8yM

[whynot]

Airbag deployment is a serious event. Just check out Google Scholar for some articles

http://scholar.google.com.au/scholar...+Scholar&hl=en

That said, in an Australian context, where an engineering assumption is made that occupants are restrained by a seat belt, airbag deployment is often the last roll of the dice.

[Kryton]

In the early days of airbags in the U.S, their airbags were going off at over 300mph in a split second - straight into your face.
In most cases they were doing more harm than good.
Thanks to this, airbags are now what they are today, more safer and not as fast (fast enough to work though).

Originally Posted by Fev

There are sensors in the bumpers usually like a switch. When an impact occurs that is strong enough to make the two contacts in the switch complete a circuit it sets off the airbags.

Not even remotely true at all.
It all works on deceleration as already mentioned.

[Sizey]

AUXR is dead on the money. In simple terms, an airbag is a pirotechnic that is inflated via sensors behind the front bumper.

It produces extreme heat and sudden movements so sitting too close can produce burns, broken nose or even a broken neck.

The bang is that loud that people suffer shock and can often not remember the actual impact, just the airbag. It can also produce short term hearing loss.

[deesun]

Originally Posted by davway

In the early days of airbags in the U.S, their airbags were going off at over 300mph in a split second - straight into your face.
In most cases they were doing more harm than good.
Thanks to this, airbags are now what they are today, more safer and not as fast (fast enough to work though).
Not even remotely true at all.
It all works on deceleration as already mentioned.

Early US airbags were considerably larger in size to ours because they had to stop a person without a seatbelt on so the explosion and subsequent possibility of injury. Most stories of severe injury came out of the US and from early airbag deployment.

[388cube_edxr8]

Don't forget that the US airbags were/are considerably larger because statistically the average US citizen is considerably larger and heavier

[Mickxr8]

one thing that has always interested me is what happens to that big bit of plastic on your steering wheel/passenger side thing when they go off ?

[Kryton]

Originally Posted by mickxr8

one thing that has always interested me is what happens to that big bit of plastic on your steering wheel/passenger side thing when they go off ?

It rips open.
Notice your steering wheel has an indented line in the middle - that is where it will rip and release the airbag when it goes off.

[geckoGT]

Originally Posted by Mr Hardware

Correct. We had a cabbie once was in a medium sized accident, had the airbag go off, burns up his arms. He was off work for a week or two. Apparently if he hadn't have had an airbag, he would have been fine and back at work the next day.

It is true that injuries can be sustained when airbags deploy. In case where people are positioned in the car correctly and holding the steering wheel correctly, these are most commonly minor burns similar to carpet burns as the fabric of the bag rubs against skin as it flies out. No they will not cause 3rd degree burns (or full thickness burns in the new speak) due to the pyrotechnic device, it is only a small charge to produce gas which does not get hot enough to cause burns. By the way, when a airbag deploys it is not smoke that fills the cabin, it is powder that they use to preserve the fabric of the bag. I do not know how many times we get called to a crash involving a vehicle fire and it is just airbag powder.

To sustain a burn severe enough to require a few weeks off work the cabbie would have had to have his hands incorrectly placed on the wheel, most likely at the top of the wheel with his forearms hanging over the horn pad area. I have seen a similar injury to this a couple of times, one case did not involve 3rd degree burns, they were actually 2nd degree (now called partial thickness) but did involve an uncomplicated fracture of the radius and ulnar bones as well. The others involved similar burns and heavy bruising.

The largest problem with airbags is not actually the air bag, it is the persons driving position.

The major driving fault I come across is incorrect hand position. Most steering wheels these days have shaping of the rim that makes the 3 and 9 position the most comfortable. There is a reason for that, it encourages you to hold the wheel in the most effective hand position for vehicle control, comfort and airbag function. Hold the wheel in this area and the worst you will receive is mild burns. The 10 and 2 position that used to be taught is too high on the wheel and besides being less effective in terms of vehicle control, also brings the fore arms too close to the deployment area of the airbag. Higher on the wheel than that (like both hands at the top) gives crap vehicle control and places the forearms directly over the airbag, severe burns and often fractures happen here.

The other common fault I see is people sitting too close to the wheel, most frequently shorter people. Most of the time it is because they move the seat forward to get correct reach to the pedals but they do not move the steering column forward. Have a look around and you will see them often, driving along with the steering wheel so close they are hugging it with their arms having massive bends at the elbows. The correct position is with the hands at 9 and 3 on the wheel, the elbows should be slightly flexed and able to be straightened without moving your hands (this should push you harder into the back rest pad of the seat). If this arm reach is too close the steering column should be adjusted until it is correct, or the seat can inclined back a bit to achieve the same effect. Once this distance is set correctly there is no way that you can cop a hit in the face/neck/chest from a deploying airbag, they do not deploy out far enough. Not unless you are a midget and have arms 30 cm long. Now before you all claim that manufacturers should account for people that want to sit on the steering wheel, no they shouldn't. Those people that sit that close to the wheel often sustain serious chest injuries in collisions where airbags are not fitted, they do not get hit by and airbag, they hit the wheel. Sitting that close to the wheel is never safe, no matter what safety devices are fitted to the car.

My last one that blows my mind is the passenger in the front seat, driving along with the feet up on the dash or out the window, for some strange reason it normally seems to be young ladies that do this (must be suntanning their feet). To understand what happens during airbag deployment here you have to understand some of the variations between passenger and driver airbags. The passenger airbag is larger, comes out further from the dash as it is further away from the occupant and because of its larger size and need to deploy to full inflation in the same time period, deploys much faster. Now imagine that airbag deploying at over 300 km/h (the speed of airbag deployment), hitting the legs that are on the dash on the way through. There is easily enough force to shatter femurs (thigh bones) and seriously damage the pelvis. Not to mention secondary injuries when their mashed up legs gets shoved hard against their chest and rib fractures etc occur. Plain stupidity, foot wells are called that for a reason, that is where feet go.

Final advice, never put anything on the horn pad or passenger side airbag cover, such as note pads and pens etc, these become a 300 km/h missile during an airbag deployment. Sounds stupid I know but you still see people doing it, mostly delivery drivers etc.

[UNR8D]

aursome post gecko.

WIKI is your friend for detailed explanations like the one earlier provided.

[geckoGT]

Originally Posted by UNR8D

aursome post gecko.

WIKI is your friend for detailed explanations like the one earlier provided.

Thanks