Any such common carrier, or any officer or agent thereof, requiring or permitting any employee to go, be or remain on duty in violation of section 75-419, shall be liable to a penalty of not to exceed five hundred dollars for each and every violation thereof, to be recovered in a suit or suits to be brought by the county attorney of the county in the state having jurisdiction in the locality where the violation shall have been committed. It shall be the duty of such county attorney to bring such suits upon satisfactory information being lodged with him, but no such suit shall be brought after the expiration of one year from the date of such violations as may come to his knowledge. In all prosecutions under this section the common carrier shall be deemed to have had knowledge of all acts of its officers and agents. The provisions of sections 75-419 and 75-420 shall not apply in any case of casualty or unavoidable accident or the act of God; nor where the delay was the result of a cause not known to the carrier or its officers and agents in charge of such employee at the time such employee left a terminal, and which could not have been foreseen; nor to the crews of wrecking or relief trains.