N.J. Stat. § 40A:14-56
A member of the fire department and force of a municipality shall be entitled to an exempt fireman certificate when it appears that at the time of his appointment he was of good moral character and was not under 18 or over 57 years of age and that he had performed: during a period of seven years, 60% of fire duty; or after January 1, 2009, 50% of fire duty; or after January 1, 2020, a percentage rate as set by the executive committee of the New Jersey State Exempt Firemen's Association, in each year, respectively. Any member who otherwise would be eligible for an exempt fireman certificate, but who, as the result of an injury or injuries incurred out of or in the course of fire duty, is permanently unable to fulfill the seven-year performance requirement set forth in this section, shall be entitled to an exempt fireman certificate if, at the time he incurred the injury or injuries, the member had performed: during a period of five years, 60% of fire duty; or after January 1, 2009, 50% of fire duty; or after January 1, 2020, the percentage rate as set by the executive committee of the New Jersey State Exempt Firemen's Association, in each year, respectively. In cases where the appointment was made during the war years the age limit shall be extended 10 years. Service in the United States Armed Forces during the war years shall be considered as fire duty service.
Service in more than one municipal fire department, for separate periods not concurrent, amounting in the aggregate to seven years, shall be deemed equivalent to seven years' service in a single municipal fire department and any fireman so serving shall be entitled to an exempt fireman certificate from the department and force in the municipality wherein he is serving at the time when he becomes entitled to the certificate. The prior service shall be certified by the chief executive officer of the municipality or municipalities wherein the member served and attested by the municipal clerk or clerks.
N.J.S. § 40A:14-56