N.J. Stat. § 43:16A-5.2
The retirement of a member of the Police and Firemen's Retirement System, established pursuant to P.L. 1944, c.255 (C.43:16A-1 et seq.), who (1) on the date of retirement has attained the service retirement age applicable to that member and is a volunteer firefighter or first aid worker, rescue squad worker, or emergency medical technician serving as a volunteer in the same jurisdiction; and (2) remains a volunteer firefighter or first aid worker, rescue squad worker, or emergency medical technician serving as a volunteer after the date of retirement as long as the employee's job duties were substantially different or, if the employee's job duties were similar, the employee has a break in service of at least 30 days after retirement, shall be a bona fide severance from employment, notwithstanding that the retired employee maintains the relationship of a volunteer firefighter or first aid worker, rescue squad worker, or emergency medical technician serving as a volunteer with the same employer from whose employment the member retired. This act shall be effective if the qualified status of the retirement system under federal law can be maintained upon its application, and such modifications to the system as may be available shall be made to allow for its application.
Notwithstanding any other provisions of law to the contrary, the provisions of this section shall not be construed to permit a paid firefighter employed by a part-paid fire department to serve as a volunteer with the department from which the paid firefighter retired.
N.J.S. § 43:16A-5.2