This document provides a uniform reference for tertiary structure items when a tertiary structure is designed and constructed in offshore oil and gas projects. This document covers topside systems for fixed or floating offshore projects not covered by class requirements. This document can be applicable for hull systems and onshore projects when there is consent from relevant stakeholders. This document does not provide class rules from classification societies. This document provides requirements on dimensions of the items but does not include requirements on clearances with other structures. The following tertiary outfitting designs for equipment items are covered in this document: — handrails; — safety gate; — stairs; — spiral stairs; — vertical ladder; — grating; — maintenance hole (manhole); — connection method.