N.J. Stat. § 40A:14-35
The governing body of a municipality may appropriate such sums of money as shall be deemed necessary to aid a municipal paid or part-paid fire department and force in an adjoining municipality, or to aid a board of fire commissioners in a fire district or an independent or a volunteer fire company in an adjoining municipality if such department and force, or fire district or company own and maintain their own apparatus and equipment and habitually respond to fires in the first named municipality.
In any instance wherein any of the members of such a fire department and force, fire district or fire company are either answering or returning from a call for the purpose of aiding an adjoining municipality they shall not be liable for personal injuries or property damages caused by them in rendering such aid.
N.J.S. § 40A:14-35