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There are many reasons a surface buoy may be on location, such as met-ocean, structure marker or anchor buoys. They are generally in place to provide a warning of potential danger and should be equipped with lighting, high visibility colour and radar reflectors. Any buoy will be anchored to the seafloor through use of chain, anchor, or they may be attached to a structure.

A subsea valve is a device which either isolates or regulates the flow of material. They are most commonly integrated into manifolds, but are occasionally found as stand-alone structures. Stand-alone subsea valves are most commonly found towards the ends of pipelines or close to pipeline junctions. Typical valves will be 1 metre wide and 1 to 2 metres high, although larger Isolation Valves may be 8 metres wide and up to 5 metres high.

A Towhead is a structure that is pre-fabricated onshore and is found at either end or in the middle of a pipeline Bundle and allows that bundle to be towed to site. The smallest are approximately 8 metres in length and 3 metres high, weighing approximately 100 tonnes. The largest are approximately 40 metres in length and 8 metres high, weighing over 500 tonnes.

A semi-submersible rig is a mobile offshore drilling unit. The purpose of the rig is to drill new wells, alter existing wells, or suspend or abandon older wells. A semi-submersible rig has no propulsion system and must be towed to location. When on location, anchors are deployed, often extending outside of the 500 metre safety zone. Semi-submersibles can be used in greater water depths – not requiring foundations to the seabed.

An Emergency Response and Rescue Vessel, (ERRV) also sometimes known as a ‘Standby’ Vessel, is a ship, required by UK law to be on duty at each offshore installation, 24 hours a day, 365 days a year. They commonly range in size from 50 metres to 100 metres in length and provide support to recover persons following evacuation, rescue persons near the installation and take such persons to a place of safety.

A 500m subsea safety zone is an area extending 500m from a given point of a subsea installation in the United Kingdom Continental Shelf. They are established following an order created by statutory instrument. These safety zones are 500 metres from a central point. Vessels of all nations are required to respect them. It is an offence to enter a safety zone except under special circumstances.

A jack-up rig is a mobile offshore drilling unit. The purpose of the rig is to drill new wells, alter existing wells, or suspend or abandon older wells. A jack-up rig has no propulsion system and must be towed to location. The legs of a jack-up rig can be fully lifted while it is towed and lowered when operating so the hull is out of the water. A jack-up rig always has a 500 metre safety zone.

A production manifold is a subsea structure containing the valves and pipework to direct produced fluids from several wells into one or more pipelines. A typical production manifold might be up to 25 metres long, 20 metres wide and 7 metres high, weighing around 300 tonnes. As production manifolds normally connect a cluster of subsea wells they are most commonly found within 500m safety zones.

Driven Pile Anchors are used to anchor a wide range of surface structures in place, including fixed Platforms and Floating Production Storage and Offloading vessels (FPSOs). The pile is a hollow steel pipe that is installed into the seabed, varying in size from 25 to 45 metres in length and 45 centimetres to 2.5 metres in diameter. When installed, they may project 2 metres above the seabed and several hundred metres outside of a 500 metre Safety Zone.

A 500m surface safety zone is an area extending 500m from any part of an offshore oil & gas installation in the United Kingdom Continental Shelf. They are established automatically around all installations which project above the sea at any state of the tide. Vessels of all nations are required to respect these Zones. It is an offence to enter a safety zone except under special circumstances.

A Platform is the generic term given to any fixed facility that breaks the surface of the sea. They may be of either steel template or concrete construction. ‘Platforms’ may be manned or unmanned and they may have production facilities containing dangerous hydrocarbons, or accommodation quarters. All platforms will have a 500 metre safety zone which should not be entered other than in specified circumstances.

Subsea wellheads are the components of a well at and above the seabed. Once a well has been drilled, it is completed to provide everything that the well requires to enable production. The primary purpose of the wellhead is to control the flow of well fluids during drilling and production. Subsea wellheads with production trees may be 4 metres wide and project 5 metres above the seabed. They may weigh 70 tonnes.