Isn't it amazing how FPSO's are built? The scope of the construction is daunting plus you still need to consider the weight, footprint, industry requirements and scheduling of the project. The control and safety system is part of this huge task and by making it modular, it allows distributed construction, faster commissioning and improved flexibility, among others.
Now, some people would say, use Remote I/O to achieve modularity... But there are several reasons why using the Modular Safety Concept is better, such as having local control or accurate time stamping of alarms and events even if the communication link is lost. You can read more about these advantages on page 20 - 23 of the Modular Safety Concepts for Marine & Offshore Applications whitepaper.
Of course, safety and reliability are very important considerations. So, this solution is implemented using redundant components by default, complies to strict requirements on F & G System and central / local power distribution design.