What an Airbag Actually Does in a Car Crash

An airbag rapidly inflates and then vents to slow and spread out your body’s deceleration so you don’t strike hard interior surfaces; it works together with your seat belt to reduce head and chest injuries. In a collision, sensors trigger a tiny pyrotechnic inflator that fills the bag in a few milliseconds, allowing you to “ride down” the crash with lower peak forces and reduced risk of fatal injury.

How an Airbag Works, Step by Step

The sequence below outlines what happens in the fractions of a second during a crash, from detection to deployment and deflation.

1. Impact detection: Accelerometers and pressure or crush sensors register a rapid change in speed and direction consistent with a crash.
2. Decision algorithm: The airbag control unit calculates severity, direction, and occupant/belt status to decide whether to deploy and at what power level.
3. Inflation: A pyrotechnic inflator ignites solid propellant (modern systems use non-azide formulas) to create gas that fills the bag in roughly 20–40 milliseconds.
4. Catching and venting: You contact the bag as it inflates; tethers shape it and vents release gas to absorb energy, limit rebound, and control head/chest deceleration.
5. Deflation and shutdown: The bag rapidly deflates within about 100–200 milliseconds; the system logs the event and disables further deployments for that ignition cycle.

The entire event is over in well under a quarter of a second, timed to match your forward motion so the bag cushions rather than “punches” you.

Why It Reduces Injuries: The Physics

Airbags don’t make crashes gentle; they make them survivable. By increasing the time over which your momentum is brought to zero, an airbag lowers the peak force on your head, neck, and chest. The fabric spreads load over a larger area, and controlled venting reduces rebound. This complements the seat belt, which keeps you positioned, limits torso movement, and triggers pretensioners. Together, belts and frontal airbags reduce the risk of fatal injury significantly for front-seat occupants; airbags add roughly a low-teens percentage risk reduction on top of belts in frontal crashes. Importantly, an airbag is not a soft pillow—initial contact is firm because effective energy absorption requires pressure before the bag vents.

When It Deploys—and When It Doesn’t

Airbag deployment depends on crash severity, direction, and occupant factors. The following points summarize typical behavior for modern “advanced” systems.

• Frontal airbags deploy in moderate to severe frontal or near-frontal crashes; thresholds vary by vehicle but are often equivalent to hitting a rigid barrier at roughly low-to-mid teens mph when belted, higher if unbelted.
• They typically do not deploy in low-speed bumps, minor rear-end collisions, or many side impacts; side/thorax or curtain airbags handle side hits and rollovers.
• Dual- or multi-stage inflators and algorithms modulate output based on crash intensity, belt use, seat position, and occupant size.
• Advanced systems can suppress the front passenger bag if a child or a very light occupant is detected, or if a rear-facing child seat is present.

Not seeing a deployment after a minor crash is usually normal—it signals the crash wasn’t severe or properly oriented for that airbag, not that the system “failed.”

Types of Airbags in Modern Vehicles

Protection has expanded well beyond the steering wheel and dashboard. Here are common airbag types you may encounter today.

• Frontal driver and passenger airbags (often dual-stage, adaptive).
• Side thorax airbags to protect the chest in side impacts.
• Side curtain (head) airbags that drop from the roof rail for side impacts and rollovers.
• Knee airbags to manage lower-body loads and improve occupant kinematics.
• Center airbags between front occupants to mitigate “far-side” collisions.
• Rear-occupant airbags and inflatable seat belts in some models to protect back-seat passengers.
• Pedestrian airbags (limited availability, mainly in select European models) to cushion the hood/windscreen area.

No single vehicle has every type, but newer designs increasingly add center and rear-occupant coverage to address real-world crash modes.

Limits and Risks—and How to Use Them Safely

Airbags can injure out-of-position occupants. The following practices maximize benefits while minimizing risks.

• Always wear a seat belt; airbags are supplemental, not substitutes.
• Sit at least about 10 inches (25 cm) from the steering wheel; keep the seatback upright and lower the wheel if possible.
• Hold the wheel at roughly 9 and 3 o’clock to reduce arm/face injuries during deployment.
• Children under 13 ride in the back; never place a rear-facing child seat in front of an active passenger airbag.
• Don’t put feet on the dashboard; keep knees clear of knee airbags.
• Heed the SRS/airbag warning light; if it stays on, have the system inspected promptly.
• Check your VIN for recalls (notably for older Takata inflators) via your national safety authority; repairs are free where recalls apply.

Following these basics preserves the airbag’s intended timing and geometry so it can manage forces effectively.

Maintenance, Lifespan, and After a Deployment

Airbag systems are largely maintenance-free, but certain events and signals demand attention. Consider the points below for ownership and post-crash actions.

• Airbags are designed to last the vehicle’s life; there is no routine replacement interval in modern cars.
• After any deployment, replace the airbag module, control unit if required, sensors, seat belt pretensioners, and related trim per manufacturer procedures—never reuse deployed or salvaged units.
• The white “powder” seen after deployment is usually cornstarch or talc used to help the bag unfurl; ventilate and avoid inhalation, as it can irritate eyes and lungs.
• If the SRS light illuminates, do not ignore it; a fault can disable or mis-time a deployment.

Only qualified technicians should service SRS components; DIY work can be dangerous and may render safety systems inoperative.

Common Misconceptions

Misunderstandings about airbags can lead to risky behavior. Here’s what to keep straight.

• “Airbags are soft pillows.” In reality, they’re firm on initial contact and then vent to absorb energy.
• “Airbags make seat belts unnecessary.” Belts are the primary restraint; airbags add protection but are not a replacement.
• “They always go off in any crash.” Deployment depends on crash type and severity; many collisions don’t require an airbag.
• “Once the light goes off, it’s fine to drive indefinitely.” A lingering SRS light means a fault; get it checked.

Accurate expectations help you use the system as intended and interpret what happens in a crash.

Summary

An airbag’s job is to buy you time and space in a crash: it inflates in milliseconds to catch and decelerate you more gently, distributes forces across stronger body areas, and vents to avoid rebound. It’s engineered to work with your seat belt, activate only when needed, and adapt to occupant size and crash severity. Used correctly—and with recalls addressed—airbags have saved thousands of lives and remain a cornerstone of modern vehicle safety.

What do air bags do in a crash?

Air bags are designed to keep your head, neck, and chest from slamming into the dash, steering wheel or windshield in a front-end crash. They are not designed to inflate in rear-end or rollover crashes or in most side crashes.

What does an airbag do in a crash?

Air bags reduce the chance that your upper body or head will strike the vehicle’s interior during a crash. To avoid an air-bag-related injury, make sure you are properly seated and remember—air bags are designed to work with seat belts, not replace them. And children under 13 should sit in the back seat.

At what speed do airbags deploy in an accident?

Typically, airbags will deploy in collisions at speeds over 10 miles per hour. For example, if you hit a stationary object or are involved in a rear-end collision, the airbags may go off. However, seat belts alone may be enough to keep you safe in these crashes, and the airbags might not deploy.

Do airbags actually save you?

Numerous studies have confirmed the effectiveness of airbags in preventing death and injury, especially in combination with seat belts (Viano, 2024). NHTSA estimates that 4,330 lives were saved by frontal airbags in 2019 alone (Kahane & Simons, 2024).