Dye marker (20g), which leaves a dyed trace in water, thus significantly increasing the chances of being spotted by a rescue boat or plane. The fluorescein (more accurately the fluorescein salt, CAS 518-47-8) is a dye that can even in small amounts intensively color the water green or even yellow-green, and it additionally shines in sunlight. The use of fluorescein for rescue from the sea has its origins in the second world war, where it has saved the lives of many pilots of all the involved countries.
Fluorescein is not harmful in the form of the dilution used for signalizing (in some countries it is approved as a food coloring). When using pure or a high-concentration substance can however lead to a poisoning. Under the directive (ES) num. 1272/2008 it is not considered a dangerous substance or mixture. When judged by the 67/548/EHS directive, it is not considered a dangerous substance.
The ampoule with fluorescein is water proof and can be permanently stored in for example the pocket of a diving jacket or a dry suit. Each package is tested under the pressure in the depth of up to 100 meters.