API RP 74 pdf download Recommended Practice for Occupational Safety for Onshore Oil and Gas Production Operation 3.7cellar: Excavation around the wellhead to providespace for items of equipment at the top of the wellbore. 3.8Christmas tree: The valves and fittings assembled atthe top of a completed well to control the flow of hydrocar-bons and other fluids. See API Spec 6A....