In the absence of the Chief, the First Assistant Chief shall assume the duties of the Chief; in the absence of the First Assistant Chief, the Second Assistant Chief shall assume the duties of the Chief. The Chief or his substitute shall be on duty and on call at all times. In the event of the Chief’s absence from the City, he shall appoint one of his assistants to have charge of the Fire Department during his absence. The Assistant Chiefs shall notify the Chief in the event of their absence from the City.