What is the fine-grained topic of the following text: Beginning with 2008 models built after May 2007, modifications were made to the side tubular head protection airbags to improve occupant protection in side-impact crashes (note: information about when a specific vehicle was manufactured is on the certification label typically affixed to the car on or near the driver door). Only return the topic.
Modifications to side tubular head protection airbags in 2008 models for improved safety in side-impact crashes.