An Isolated Danger Mark, as defined by the International Association of Lighthouse Authorities, is a sea mark used in maritime pilotage to indicate a hazard to shipping such as a partially submerged rock.
It is recognisable by its black and red bands and top-mark of two black balls.
Its distinctive sequence of flashing white light consists of 2 quick flashes in intervals of either 5 or 10 seconds.
- International association of maritime aids to navigation and lighthouse authorities (2010). "Maritime buoyage system and other aids to navigation" (PDF). IALA-AISM. Retrieved 11 August 2019.
- Service Hydrographique et Océanographique de la Marine (1 September 2016). Signalisation Maritime (PDF). Ouvrages Généraux (in French). France: SHOM. ISBN 978-2-11-139457-5. Retrieved 11 August 2019.
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