Final answer:
A certified professional engineer, the system manufacturer, and a competent person authorized by either are all qualified to inspect a system and declare it safe for use.
Step-by-step explanation:
In the context of inspecting a system and determining its safety for use, all of the above parties mentioned are authorized to inspect a system and deem it safe. A certified professional engineer is trained to evaluate the safety and compliance of systems according to industry standards. The system manufacturer typically has detailed knowledge of their product and can provide specific safety assurances and guidance. Lastly, a competent person authorized by either of the aforementioned, meaning someone who has the necessary skills, knowledge, and authorization, can inspect the system.