N.H. Rev. Stat. Ann. § 109:6

No municipality whose fire-fighting forces, pursuant to the provisions of this chapter, are rendering emergency fire assistance to another municipality or state, shall be liable by reason of any act or omission on the part of such fire-fighting forces while so engaged; or on account of the maintenance or use of any equipment or supplies used in connection with the rendering of such assistance; nor shall any fire commissioner, fire chief, or other superior officer of a fire department, a fire company or any unit of municipal fire-fighting force, acting pursuant to the provisions of this chapter, be liable by reason of any act or omission on the part of any of his subordinates when they are rendering emergency fire assistance, under the command of an officer other than himself, in a municipality other than that in which they normally are employed.