  Major accidents (e.g., the Space Shuttle Challenger disaster in the USA, the
Bhopal Disaster in India, Fukushima nuclear accident in Japan, Tianjin Port
fire and explosion accident in China) have occurred all over the world. Safety
scientists are always trying to understand why these accidents happened and how
to prevent these accidents. Accident models and theories form the basis for
many safety research fields and practices such as investigation of accidents,
design of a safer system and decision making on safety related field. There is
no universally accepted model with useful elements relating to understanding
accident causation, although many accident causation models exist. Based on
STAMP and RMF, we proposed a new theory named the Interaction Theory of
Hazard-Target System (ITHTS) that incorporate human, organisational and
technological characteristics in the same framework. Accident analysis methods
provide the necessary information to analysis the accident in a specific
setting. In order to solve the issues that current accident analysis methods
still face, we proposed a new systemic accident analysis method based on ITHTS
and STPA. We choose Tianjin Port fire and explosion accident in China as a case
study to demonstrate the viability of the Interaction Theory of Hazard-target
System and the applicability of the new accident analysis method. It is
concluded that ITHTS can explain the phenomena in safety practice and the new
accident analysis method can be application in the explanation and analysis of
major accident.
