How airbags work in a car: how they save lives

Airbags are one of the key elements of passive safety in modern cars. They reduce the risk of fatal injuries in road accidents by 30-50%, but few people know exactly how they work. In this article we will analyze the physics of operation, types of airbags, their deployment speed and what happens in a split second between the impact and the protection of passengers.

Many people mistakenly think that airbags are triggered by a strong push or impact from the bumper. In fact, the process is much more complicated: it involves shock sensors, squibs, SRS control unit (Supplemental Restraint System) and even algorithms that take into account the position of the passenger’s body. We will analyze each stage - from the moment of collision to the full inflation of the airbag, and also answer questions: why they sometimes do not work, whether they can be repaired after activation and how to check their functionality.

We will pay special attention critical mistakes that drivers make when servicing the airbag system — from ignoring the indicator SRS on the dashboard before attempting to repair the squibs yourself. These actions can lead to system failure at the most critical moment.

Physics of actuation: what happens in 0.03 seconds

The deployment time of an airbag is measured in milliseconds. For comparison: a person blinks in about 100-150 ms, and the pillow manages to inflate and absorb the shock within 20-30 ms. Let's look at the process step by step:

1. Impact detection. Sensors (accelerometers) record a sharp deceleration of the car. In modern systems they are installed in the front of the body, doors and even under the seats.
2. Data analysis. Block SRS compares indicators with embedded algorithms. For example, the driver's airbag deploys in the event of a frontal impact at a speed 20-25 km/h and higher, and side ones - with a force equivalent to an impact at speed 10-15 km/h.
3. Activation of the squib. An electrical impulse heats a special composition (usually sodium azide or nitroglycerin), which instantly decomposes with the release of gas (nitrogen or argon).
4. Inflating the pillow. The gas fills the nylon bag, breaking through the protective cover on the steering wheel or panel. The pillow expands at speed 200-300 km/h!
5. Deflation. Via 0.3-0.5 seconds the gas escapes through holes in the fabric so as not to block the view or suffocate the passenger.

It’s interesting that in premium cars (for example, Mercedes-Benz S-Class or Volvo XC90) are used multi-stage pillows. They operate with different strength depending on the severity of the accident: with a light impact they inflate by 60-70%, with a strong impact - by 100%. This reduces the risk of injury from the pillow itself.

Types of airbags: not only front

The first serial pillows appeared in Mercedes-Benz W126 in 1981 - then it was only a front airbag for the driver. Today, cars are equipped with up to 10 or more different types of airbag. Let's look at the main ones:

• 🚗 Frontal - the most common. Installed in the steering wheel (driver) and front panel (passenger). In some models (for example, Toyota Camry) the passenger airbag has two inflation levels.
• 🪑 Lateral — mounted in the backs of the front seats or door cards. Protects against side impacts (for example, during “cross” accidents).
• 🧠 Head (blinds) — open along the ceiling, protecting the head in case of a side rollover or impact. Typically cover the area from the front to rear pillars.
• 👶 Knees — prevent injuries to the driver’s legs in a frontal collision. Found in Honda Accord, BMW 5 Series.
• 🛋️ Central - installed between the front seats (for example, in Volvo S60). Protect passengers from colliding with each other.
• 🚼 Rear side - a rare type, found in premium cars (for example, Audi A8). Protects second row passengers.

Pillow type	Installation location	Response speed (ms)	Gas volume (liters)
Front (driver)	Steering wheel	20-30	30-50
Front (passenger)	Front panel	25-35	60-100
Lateral	Seat back/door	10-15	15-25
Curtain (head)	Ceiling	15-20	40-60

Important: in budget cars (for example, Lada Vesta or Renault Logan) often only front airbags are installed. Side and curtains are found in luxury trim levels or in cars of a higher class (from C-segment). When buying a used car, be sure to check which airbags are installed and whether they have deployed previously.

When airbags do NOT deploy: common reasons

Airbag failure is one of the leading causes of serious injuries in road accidents. According to statistics Research Institute of Automotive Electronics, in 15% of accidents airbags do not work due to technical faults. Main reasons:

• ⚡ Disabled SRS system. For example, after an accident, the previous owner could turn off the airbags for safe repairs, but did not turn them back on. You can check this by a burning light bulb SRS on the dashboard.
• 🔋 Low battery. The airbags require high voltage to trigger the squib. If the battery is weak (below 9 V), the system may not work.
• 🛠️ Incorrect repair. After the airbag is deployed, many “masters” simply replace the bag without checking the sensors and wiring. This leads to false positives or failures.
• 🚗 Hit at the wrong angle. Front airbags do not deploy in side or rear collisions. For example, if you are hit in the bumper from behind, the airbag will not open.
• 📉 Service life has expired. Manufacturers recommend changing pillows every 10-15 years, even if they didn't work. Over time, the gas-generating composition loses its properties.

⚠️ Attention: If the indicator on the dashboard is on or flashing SRS/AIRBAG, this means critical failure systems. Operating a car in this condition is dangerous - the airbags may not work in an accident or, conversely, work spontaneously.

Common mistake: drivers ignore the light bulb SRS, thinking it was an “electronics glitch.” In fact, even if the airbags are visually intact, the fault may lie in the sensors, control unit or wiring. Diagnostics must be carried out using specialized equipment (for example, Launch X431 or Autel MaxiSYS).

What to do if the airbag deployed without an accident?

If the airbag opens spontaneously (for example, during heavy braking or on a bump), this indicates critical failure squib or sensors. Immediately:

1. Disconnect the battery (remove the negative terminal).

2. Do not drive - the other airbags may deploy at any time.

3. Tow the car to a service center for a complete diagnosis of the system SRS.

Can airbags be repaired after deployment?

After activation of the airbag, it You can’t just “sew it up and put it back in”. This is due to several factors:

1. The squib is disposable. Once triggered, it is destroyed and cannot be repaired. Needs replacement with a new one.
2. The pillow fabric loses its strength. When opened, the bag experiences enormous loads. Even if it is sewn up, it may tear the next time it is triggered.
3. Sensors require recalibration. After an impact, impact sensors may give false signals. They need to be checked and replaced if necessary.
4. The SRS unit records an error. A fault code remains in the control unit's memory, which must be reset using a special scanner.

The cost of restoring the system after a trigger:

• 💰 Replacing the driver's airbag: 15 000–40 000 ₽ (depending on the car model).
• 💰 Replacing the passenger airbag: 20 000–50 000 ₽.
• 💰 Replacement of side cushion: 10 000–30 000 ₽.
• 💰 Diagnostics and error reset: 3 000–10 000 ₽.

⚠️ Attention: Buying used pillows at salvage yards - dangerous economy. The squibs in such products may be faulty or expired. When triggered they may explode, causing additional injuries.

The only safe option is to buy new original pillows or certified analogues (for example, TRW, Autoliv). After replacement, the system must be tested using diagnostic equipment.

Install new squibs and airbags|Check the integrity of the wiring and connectors|Reset errors in the SRS unit with a scanner|Test the shock sensors on the stand|Make sure that the SRS indicator does not light up after starting the engine-->

Myths and misconceptions about airbags

There are many myths surrounding airbags that can cost lives. Let's look at the most common ones:

• 🚫 "The airbags deploy in any accident." In fact, they are activated only by impacts of a certain force and direction. For example, in a head-on collision at speed below 20 km/h the pillows may not inflate.
• 🚫 "The airbag replaces the seat belt." Pillows complement belts, but do not replace them. Without a seat belt, the passenger may suffer injuries from the airbag itself (for example, a broken nose or ribs).
• 🚫 "Pillows are dangerous for children." The danger is not the pillow itself, but improper transportation of a child. Children under 12 years of age must not sit in the front seat or use a rear-facing child seat.
• 🚫 "After the airbag deploys, you can drive without repair." The absence of an airbag increases the risk of death in an accident by 70%. In addition, a faulty system may cause false alarms.
• 🚫 “The pillows last forever and require no maintenance.” Manufacturers recommend checking the system SRS every 50,000 km or once every 5 years.

Another common myth: "Pillows can be turned off with a button". In most cars, only passenger front airbag (for installing a child seat). It is impossible to disable all airbags without interfering with the electronics.

How to check airbag functionality

Check system status SRS You can do it yourself and in the service. Let's start with simple steps:

1. Visual inspection. Check:
   • There are no cracks or signs of repair on the steering wheel or dashboard (this may indicate a previous operation).
   • Indicator AIRBAG or SRS The indicator on the dashboard goes out 3-5 seconds after starting the engine.
   • The seat belts are not torn and retract normally.

Error checking. Connect a diagnostic scanner (for example, ELM327 with the program Torque Pro). Error codes associated with SRS, usually start with:

• B1xxx - faulty airbags;
• B2xxx — problems with sensors;
• Uxxxx — communication errors between blocks.
• Sensor test. At the service station, they check the response of sensors to vibration and shock using special equipment.

If you're buying a used car, be sure to request an accident history (via traffic police or services like Autocode). Even after a minor accident, the previous owner might not restore the pillows, but simply “disguise” their absence.

⚠️ Attention: Never try to check the airbags “manually” - for example, by applying voltage to the connectors. This may lead to uncontrolled operation and injuries. Diagnostics must be carried out by a specialist with certified equipment.

What to do after an accident: steps to check airbags

If you are involved in an accident, even a minor one, follow these steps:

Inspect the interior for signs of deployment (torn trim, powder from the squib)|Check the SRS indicator on the dashboard|Do not turn on the ignition if you suspect damage to the wiring|Contact a service for diagnostics, even if the airbags did not deploy|Keep receipts for repairs - this will be needed for the insurance company-->

If the airbags have deployed:

1. Do not attempt to remove any remaining powder (it is non-toxic but may cause skin irritation).
2. Disconnect the battery to prevent other airbags from inadvertently deploying.
3. Take photos of the interior for the insurance company.
4. Contact a service that has experience working with SRS. Ask for certificates for spare parts.

Important: if the airbags did not deploy in an accident where they should have, this is a reason for independent examination. The system may have been faulty and you may be entitled to compensation from the seller (if the car is under warranty) or the insurance company.

FAQ: Answers to frequently asked questions

Is it possible to install airbags in an old car that did not have them?

Technically possible, but inappropriate. To do this you will need:

• Install the control unit SRS;
• Install wiring and shock sensors;
• Introduce squibs into the steering wheel, panel and seats;
• Configure the system for a specific model.

The cost of such work often exceeds 100 000–150 000 ₽, and the reliability will be lower than that of the factory system. It is better to spend this money on buying a more modern and safe car.

Why does an airbag smell like burning after deployment?

The burning smell is caused by combustion gas-generating composition in the squib. Usually this sodium azide or other substances that release nitrogen or argon when heated. The smell itself is not toxic, but can cause respiratory irritation. It is recommended to ventilate the interior after activation.

Is it possible to wash the interior after the airbags deploy?

Yes, but with caution. Powder from the squib (usually talc or starch) is not toxic, but can clog vacuum cleaner filters. To clean:

• Use a vacuum cleaner with HEPA filter;
• Wipe the surfaces with a damp cloth (not wet!);
• Avoid harsh detergents - they can damage the plastic.

If there are greasy stains (from squib grease), use isopropyl alcohol.

What are "adaptive airbags"?

These are pillows with two-stage operation, which adapt to the conditions of the accident. For example:

• When struck lightly they inflate 60-70%;
• With a strong impact - on 100%;
• The seat position and passenger weight are taken into account (via sensors in the seats).

Such systems are installed in premium cars (BMW 7 Series, Audi A8) and some crossovers (Volvo XC60).

How does steering wheel tuning affect the operation of the airbag?

Installing a non-original steering wheel (for example, sports or heated) can lead to:

• Violation of the squib circuit;
• Incorrect deployment of the pillow (if the geometry has changed);
• False alarms due to vibrations.

If you are planning tuning, choose steering wheels with a certificate ECE R12 or SAE J1400, which guarantee compatibility with SRS.