The absence of the contractor for the work shall in no way relieve him of his responsibility, but he shall be bound by the act of his employees. At all times when work is in progress and in the absence of the contractor, his agent or legal representative, there shall be a foreman or head workman at the job site, and instructions given to such foreman or head workman shall be considered as having been given to such contractor. (Prior code § 27-41)