N.H. Rev. Stat. Ann. § 356:6

No person called as a witness to testify at any proceedings under this chapter shall be excused from testifying, or from producing any books, papers or documents which are material, on the ground that his testimony will tend to incriminate him; but no person shall be prosecuted or subjected to any penalty or forfeiture for or on account of any transaction, matter or thing concerning which he may testify or produce evidence, documentary or otherwise, in any such proceeding.