When must a car seat be replaced according to safety regulations?

A car seat must be replaced if the airbag is deployed in an accident because this indicates that the vehicle experienced a significant impact that could compromise the integrity of the car seat. Car seats are designed to withstand certain forces during a crash, but deploying airbags suggests that the force exceeded safe parameters, potentially damaging the car seat in ways that are not visible to the naked eye.

Safety regulations prioritize the child's safety by ensuring that only car seats that are known to be intact and functioning properly are used. Since a deployed airbag can signify a severe collision, replacing the car seat ensures that the child has the best protection in any future incidents.

While the other options provide different conditions for car seat replacement, they do not address the critical safety concern related to accidents and the potential for hidden damage that could affect the car seat's performance. For instance, replacing a car seat every five years isn’t specifically mandated, as the lifespan can vary based on the manufacturer’s instructions. Similarly, simply reaching a certain weight may not account for other factors like age or height, and visible damage alone may not indicate if the structural integrity of the car seat has been compromised.