An occupational health and safety management system (OHSMS) is a set of people, resources, and policies interacting in an organized way to reduce damage and losses generated in the workplace. Although there are various OHSMSs in the shipping industry, the International Safety Management (ISM) Code which is managed by the International Maritime Organization is mandatory for all shipping companies. Occupational Health and Safety Assessment Series (OHSAS) 18,001:2007 is a good alternative to strengthen the implementation performance of the ISM Code. An integrated ISM-OHSAS safety system can potentially construct a more powerful and practical OHSMS by redesigning safety procedures in ships as a workplace. This study aims to build a more comprehensive OHSMS for assessing and improving the safety at sea by coordinating the constituents of the ISM Code and OHSAS. The criteria sets of both systems are analysed using a Decision Making Trial and Evaluation Laboratory approach to reveal the relations between each other. The result of the proposed approach that represents the connections among important safety constituents may be very useful especially for shipping companies for designing their safety management processes.