To encourage and aid fire companies to maintain supplemental insurance to provide benefits when members are injured or killed while performing duties as volunteer firefighters, the board shall authorize payment of $75 per year for each motorized mobile unit of firefighting equipment, not to exceed $150 per fire company per year. Payment must be a charge against the pension trust fund and must be paid to each fire company maintaining supplemental insurance or to the organization or agency maintaining supplemental insurance for a fire company.