In order to cope with severe competition in the global market, the local ar
ea network installed inside the plant site has been connected with the Inte
rnet for exchanging business information among globally distributed plant s
ites. Though the information systems have given benefits through such open
architecture, there are various risks as the result of the application of n
etwork technologies. Much attention, therefore, has to be paid for chemical
plant failures caused by triggering from outside parties. One of the commo
n technological interests is a risk analysis method of network events that
allows illegal access to the digital control system (DCS), In this paper, t
he authors present a unified approach to generate fault tree and event tree
structures between a network access and an anomaly of process plant. To il
lustrate the validity of the proposed method, a typical networked chemical
plant is taken as an example and analyzed. The present research will make c
lear what parts are most important for the plant security. (C) 2000 Elsevie
r Science Ltd. All rights reserved.