I Introduction
In chemical industry, production safety is an important problem. Chemical production process may use many kinds of hazardous article, and the reaction conditions are hardly ambient temperature and pressure. If an accident happens, it will break out suddenly, spread rapidly and last for a long time. Therefore, we must try to avoid accident happens, otherwise, it will lead to serious consequences. For this purpose, we should find a way to recognize the feature of accident, and try to remove the fault before accident happens.