Emergency wreck buoy

An Emergency wreck buoy is used to warn of a new wreck which has not yet been listed in maritime documents. The buoy is expected to be deployed for the first 24-72 hours after the wreck occurs. After that time more permanent buoyage should be deployed and charts updated.
The buoy is designed to "provide a clear and unambiguous" mark of a new and uncharted danger.
Emergency wreck marks are recognisable by the following characteristics:

Pillar or spar shape.
Colour pattern of 6 to 7 alternating blue and yellow vertical stripes of equal widths.
If a topmark is attached, it is a yellow "+" shape.
Always having a light fitted which repeats an occulting alternating light characteristic of the following pattern, abbreviated as "OcAlBY":
* Blue light emitted for 1 second.
* Eclipse of 500 milliseconds.
* Yellow light emitted for 1 second.
* Eclipse of 500 milliseconds.

An emergency wreck mark may also have the word "WRECK" painted on it. No other navigation mark uses the colour blue or uses blue light.
The International Association of Marine Aids to Navigation and Lighthouse Authorities defined the buoy in response to the sinking of the and the subsequent collisions with the wreck by the Dutch vessel Nicola and Turkish-registered fuel carrier Vicky.