N.Y. Comp. Codes R. & Regs. tit. 17 § 990.15
Except as provided in this section, no member of the board or its staff shall be compelled or permitted to testify in any litigation involving any matter which is or was subject to an investigation by the board, either during or subsequent to such investigation, unless the board is a party to such litigation. Testimony of members of the board's staff may be available for use in actions or suits for damages arising out of accidents investigated by the board, through depositions or written interrogatories only. Depositions may only be taken at the board's main office, unless the board agrees to a deposition at another location. Depositions must be on notice to all parties, and must be at a time convenient to the board. Members of the board's staff may be compelled to submit to a deposition only once in connection with any accident investigation, and consequently, when more than one lawsuit arises, it shall be the duty of counsel seeking the deposition to ascertain the identity of all parties and to notify them to afford them opportunity to participate in the deposition.
N.Y. Comp. Codes R. & Regs. Tit. 17 § 990.15