I have heard that Minnesota has a decentralized pension system for volunteer firefighters. What does this mean?

Firefighters from each volunteer fire department in Minnesota have the ability to create a pension plan that is administered by a nonprofit corporation, known as a volunteer fire relief association. There are about 650 volunteer fire relief associations that currently exist, covering nearly 20,000 volunteer firefighters. By contrast, state and local government employees are covered by one of three state-wide retirement systems.