§ 118. Technical rules of evidence or procedure not required. The chairman or board in making an investigation or inquiry or conducting a hearing shall not be bound by common law or statutory rules of evidence or by technical or formal rules of procedure, except as provided by this chapter; but may make such investigation or inquiry or conduct such hearing in such manner as to ascertain the substantial rights of the parties. Declarations of a deceased employee concerning the accident shall be received in evidence and shall, if corroborated by circumstances or other evidence, be sufficient to establish the accident and the injury.