Concept of hazards is useful considering an overview of progressive process of the accident and its preventive measures. An accident occurs when, for instance, people make an error in a hazardous situation, or harmful event, resulting in damage to people, property and environment, called harm. In the past, even colleagues attempting to rescue those who had become unconscious on the inner bottom plating were involved in an accident and suffered a second disaster because of failing to measure the atmosphere and wear appropriate personal protective equipment. With advances in technology and complexity in socio-technical society, the situation of defenses in depth and human factors is deeply related to the contributing factors in most of the accidents and incidents. Apply again the case of chemical tanker accident during enclosed space entry to Swiss cheese model. Central liveware deals with the condition of operators by themselves at the time of an accident.