Complex sentence: The 8,300 volunteer firefighters belong to the 360 volunteer fire brigades, mainly serving small towns, communities and outer suburbs which career stations do not cover, and respond to 20--30% of all incidents the New Zealand Fire Service attends.
Split into simpler sentences: The 8,300 volunteer firefighters belong to the 360 volunteer fire brigades, mainly serving small towns, communities and outer suburbs which career stations do not cover. Volunteer firefighters respond to 20--30% of all incidents the New Zealand Fire Service attends.