N.H. Rev. Stat. Ann. § 281-A:50

Any person aggrieved by a decision of the commissioner who was prevented from appealing from such decision within 30 days through mistake, accident, or misfortune and not through the person's own neglect may petition the compensation appeals board, established under RSA 281-A:42-a, at any time within one year after the commissioner's decision to be allowed an appeal. Such petition shall set forth the petitioner's interest, the reason for appealing, and the cause of the delay.