When Should Side Curtain Airbags Deploy?

Side curtain airbags are engineered to deploy during moderate-to-severe side impacts and in rollovers—either detected or imminent—typically within about 12–20 milliseconds, and they often stay inflated longer (up to roughly 6 seconds) in rollovers to help prevent occupant ejection. They generally remain inactive in minor bumps, low-speed contacts, and most rear-end collisions. Below, we explain how the system decides to deploy, what situations trigger it, and when it typically will not fire.

How Side Curtain Airbags Decide to Deploy

Automakers use a network of sensors and algorithms to determine whether to deploy the curtain airbags, which are also called head-protection airbags or inflatable curtains. The decision hinges on crash severity, direction, and roll dynamics, not just vehicle speed alone.

The Sensors Involved

Modern systems combine inputs from side-impact accelerometers (measuring lateral g-forces), roll-rate and yaw-rate gyroscopes (tracking vehicle rotation), and sometimes wheel-speed and steering-angle data. These inputs are processed by the airbag control unit (ACU) hundreds of times per second.

Thresholds and Direction

Deployment typically requires a lateral change in velocity (delta‑V) and crash pulse consistent with a moderate-to-severe side collision—often equivalent to double-digit mph delta‑V, though exact thresholds vary by vehicle. For rollovers, the system looks for a roll rate/angle pattern that indicates a rollover is occurring or imminent, prompting deployment on one or both sides to reduce ejection risk.

Timing and Duration

Because occupants are close to door structures and glass, side protection must act fast: curtains generally inflate in about 12–20 ms. In events with rollover dynamics, curtains are designed to remain inflated far longer than frontal airbags—typically up to around 6 seconds—to maintain a protective barrier.

Situations That Typically Trigger Side Curtain Airbag Deployment

The following scenarios represent the most common conditions under which side curtain airbags are designed to deploy. Specific behavior varies by make and model, but these examples align with industry norms and safety regulations.

• Moderate-to-severe side impacts (T-bone collisions), including when the vehicle is struck at the doors or pillars.
• Rollover crashes or imminent rollovers detected by roll-rate/angle sensors (often deploying curtains on both sides).
• Oblique or angled crashes that generate substantial lateral forces, even if there is also forward motion.
• “Trip” rollovers from curb or soft-soil engagement that rapidly induce vehicle roll.
• Side impacts while the vehicle is stationary (for example, being struck in a parking lane) if severity thresholds are met.

In these events, the system prioritizes head protection and ejection mitigation, especially near side windows, helping reduce the risk of contact with intruding structures and broken glass.

When They Generally Do Not Deploy

Airbag algorithms are tuned to avoid unnecessary deployment, which can pose risks and increase repair costs. The circumstances below usually do not meet curtain airbag thresholds.

• Minor side scrapes or low-speed contact with a mirror or door panel that do not produce sufficient lateral deceleration.
• Rear-end collisions without significant lateral forces.
• Most frontal crashes that lack meaningful lateral components (frontal airbags and seatbelt pretensioners address these).
• Single-wheel pothole strikes or curb bumps without rollover dynamics or adequate lateral delta‑V.
• Very low-speed parking impacts and gentle nudges.

Non-deployment in these scenarios is expected and does not indicate a fault; the calibration is intended to deploy curtains only when the added head protection is beneficial.

Factors That Influence Whether Curtains Deploy

Even within similar crash types, several variables can affect the deployment decision and which side(s) fire.

• Impact side and angle: The struck side is most likely to deploy; rollovers can trigger both sides.
• Crash severity and pulse shape: Short, sharp side pulses can trigger faster; longer, softer pulses may not meet thresholds.
• Occupant position and restraint use: While curtains typically are not occupant-suppressed, seatbelts and proper seating position improve overall protection.
• Vehicle design and model-year calibration: Thresholds and logic vary; newer models often include enhanced rollover sensing to meet ejection-mitigation rules.
• System health: An illuminated airbag/SRS warning light indicates a potential fault that could prevent deployment; it should be diagnosed promptly.

Because these factors differ by manufacturer and model year, the owner’s manual and service information remain the best source for vehicle-specific behavior.

Regulatory and Safety Context

In the United States, ejection-mitigation requirements under FMVSS 226 (phased in by the 2017 model year) drove widespread adoption of side curtain airbags with rollover-capable deployment. Crash-testing programs from IIHS and NHTSA further incentivize effective head protection in side and rollover scenarios, shaping the calibration strategies found in current vehicles.

Practical Guidance for Drivers

The following steps help ensure your curtain airbags work as intended and that you’re protected if they deploy.

• Wear your seatbelt on every trip; it keeps you positioned for airbags to be most effective.
• Keep the area around roof pillars and headliner free of clips, hard accessories, or aftermarket gadgets that could interfere with curtain inflation.
• Address any airbag/SRS warning light immediately with professional diagnostics.
• After any deployment or significant crash, have the entire restraint system inspected and replaced or reprogrammed per the manufacturer (modules, sensors, pretensioners, and airbags).
• Consult your owner’s manual for vehicle-specific deployment information and safety instructions for children and child seats near side windows.

Following these practices supports the system’s design intent: rapid, reliable head protection when the crash circumstances call for it.

Bottom Line

Side curtain airbags are intended to fire in moderate-to-severe side impacts and rollovers, including some angled crashes with strong lateral forces. They are calibrated not to deploy in minor incidents or most rear impacts. Exact thresholds and behavior vary by vehicle, so consult your owner’s manual and ensure the SRS system is fault-free.

Summary

Side curtain airbags deploy rapidly in significant side collisions and rollovers to protect occupants’ heads and reduce ejection risk, often staying inflated longer during rollovers. They typically remain inactive in minor or rear impacts. Deployment depends on sensor data and vehicle-specific calibration, so keeping the SRS system healthy and following manufacturer guidance is essential for optimal protection.

At what speed do side curtain airbags deploy?

Deployment thresholds can be as low as 8 mph for narrow object crashes (e.g., trees and poles) and 18 mph for the more widely distributed side impacts (vehicle-to-vehicle crashes). Side airbags also deploy in certain types of frontal crashes.

Should airbags deploy in a side collision?

Airbags are most likely to deploy in frontal and side impacts, which pose high risks of serious injury to passengers. However, not all side impacts will trigger airbags; the impact needs to reach a certain severity threshold.

What triggers side airbags to deploy?

Side airbags often deploy when the vehicle is hit along the side with high impact. It takes quite a bit to release them, and many cars aren’t even equipped with this safety feature. The idea is that a side airbag will help prevent head or limb damage from being jostled within the vehicle.

What is the deployment interval for side airbags?

Side airbags deploy within milliseconds of a crash to provide rapid protection in a side impact, deploying at speeds as low as 8 mph in a crash with a narrow object like a pole and around 18 mph in broader side impacts, such as a collision with another vehicle. The deployment threshold varies depending on the severity and type of impact, with lower speeds triggering deployment in narrow object collisions to protect occupants from immediate danger. 
Factors influencing side airbag deployment:

• Crash type: Opens in new tabA narrow, concentrated impact (e.g., hitting a tree) has a lower deployment threshold, while a more distributed impact (e.g., vehicle-to-vehicle) requires a higher threshold. 
• Impact location: Opens in new tabSide airbags are designed to deploy very quickly, as there is a greater risk of direct contact with the vehicle’s side compared to a frontal crash. 
• Severity of the crash: Opens in new tabThe system’s sensors detect a certain level of force and severity of the collision to determine if the airbag needs to deploy. 

Deployment time and speed:

• Deployment time: Side airbags deploy in the first 10-20 milliseconds of a side crash. 
• Deployment speed: The speed at which side airbags deploy can be as low as 8 mph for narrow object crashes and around 18 mph for broader impacts. 

Why this is important:

• The rapid deployment of side airbags is crucial for protecting occupants’ heads and torsos from the impact force in a side collision. 
• The low deployment thresholds allow the airbag to provide a barrier between the occupant and the striking vehicle in a very short timeframe.