I believe the CPSC would have banned safety matches years ago if there was even an unreasonable hazard.

These are the practices I follow:

Old front strikers that have never been struck should be kept intact.

Feature matches should be kept intact even if a few sticks are missing.

Other partially used books should be shucked and the sulfur matches discarded.

Recently made matches, almost always back srikers, can be shucked and kept as flat covers.