Yellow flag (contagion)

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A yellow square, outlined in black
A yellow square, outlined in black
A "Double Quebec", flying from a ship would signal" "I require health clearance"

The "Quebec" signal flag, called the "Yellow Jack", is a simple yellow flag that was historically used to signify a vessel was, or might be, harboring a dangerous disease and needed to be quarantined (it stands for “Q”). However, in modern usage, the flag indicates the opposite, signaling: "My vessel is healthy and I request free pratique".

A ship flying two Quebecs, ie. "QQ", or "Double Quebec", is signaling: "I require health clearance". In both cases, if and when free pratique is granted, the vessel may lower the Quebec(s) and raise the national ensign of the port. With free pratique granted, the ship may do business at the port. In the event that, for health reasons, the vessel is not granted free pratique, it will continue to fly the Quebec, in effect indicating that it is in quarantine until such time as any health concern is resolved.

In International maritime signal flags, plain yellow, green, and even black flags have been used to symbolize disease in both ships and ports, with the color yellow having a longer historical precedent, being used as a color of marking for houses of infection prior to its use as a maritime marking color for disease.

It is sometimes called the "yellow jack", which became a name for yellow fever. Cholera ships also used a yellow flag.[1]

The plain yellow flag ("Q" or "Quebec" in international maritime signal flags), may derive its letter symbol from its initial use in "quarantine" but, in modern times, the flag indicates the opposite — a ship that declares itself free of quarantinable disease, and requests boarding and inspection by the relevant authorities to allow the grant of "free pratique".[2]

In cities such as Jakarta, plain yellow flags are still commonly used to mark a recent death in a neighborhood, regardless of the cause. They are placed in intersections leading to the home of the recently deceased as direction markers for mourners, and to mark the funeral convoy, so that it is given the right of way.[3]

See also[edit]


  1. ^ Mackowiak, Philip A.; Sehdev, Paul S. (November 2002). "The Origin of Quarantine". Clinical Infectious Diseases. 35 (9): 1071–1072. doi:10.1086/344062. ISSN 1058-4838. PMID 12398064.
  2. ^ "Quarantine Flag". Retrieved 2017-09-03.
  3. ^ "Yellow flag in Jakarta, powerful and unstoppable". Live in Indonesia. 2013-07-24. Retrieved 2017-12-20.

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