SUBSAFE covers all systems exposed to sea pressure or critical to flooding recovery. All work done and all materials used on those systems are tightly controlled to ensure the material used in their assembly as well as the methods of assembly, maintenance, and testing are correct. They require certification with traceable quality evidence which track the item from the point of manufacture (including all records of the creation of the product, i.e. source materials as well as smelting and hardening process for metals) to the point of installation within a SUBSAFE boundary. These measures increase the cost of submarine construction and maintenance.