Chart No. 1 · L 2
Offshore platform
Areas & limits
A platform symbol with a name marks an oil/gas structure — lit, often with a safety zone around it.
What it means
A platform symbol with its designation (name/number) marks a fixed offshore structure — production platform, rig, or similar. Many are surrounded by a charted 500 m safety zone (L 3) that vessels must not enter.
Why it matters
Platforms show a white Morse 'U' light (··—, 'you are running into danger') and foghorns. Passing inside the safety zone without business there is an offense in most jurisdictions.