Colo. Rev. Stat. § 31-30-1132
If the governing body of any municipality, fire protection district, or county improvement district, by resolution, determines that a fire department is in need of additional volunteer firefighters, a retired fire department member shall be eligible to serve as an active volunteer firefighter of such fire department. Any retired fire department member who, subsequent to retirement, serves as an active volunteer firefighter for a fire department pursuant to this section shall continue to receive pension benefits from the volunteer firefighter pension fund under this article during the period in which the person is an active volunteer firefighter of the fire department. During the period such person is receiving a pension and acting as an active volunteer firefighter pursuant to this section, such person shall not receive service credit for the purpose of increasing such pension.
C.R.S. § 31-30-1132