Sindbad

On 10 December 1979, in adverse weather, the Iraqi cargo vessel Sindbad lost its deck cargo 20 nautical miles west of Ijmuiden (Netherlands) at a depth of 30 m. Among the cargo, there were 51 steel cylinders, each filled with 1 tonne of liquefied chlorine.
 
 A search began, involving two ships equipped with side-scan sonars and in January 1980, 5 cylinders were located. The search had to be suspended. During the following four years, 7 cylinders were found and trawled but this option was abandoned due to the high corrosion of the cylinders.
 
 The Dutch authorities elaborated a special response strategy for the situation which became reality in 1984. The cylinders were located by side-scan sonars and by a remotely operated vehicle (ROV). Some of the found cylinders were moored to a safer place on the seafloor. Divers then placed explosives under each cylinder, which was then blasted in controlled conditions. The chlorine rose to the surface and, in one hour, a cloud developed, stretching 300 m wide, 3,000 m long and 300 m high. It was made more clearly visible by releasing ammonia from a ship upwind. The reaction between ammonia and chlorine formed a clearly visible white cloud of ammonium chloride.
 
 Single seabirds were occasionally observed flying into the gas cloud and falling immediately like stones to the water surface but no serious ecological damage was detected from chlorine. The total cost for the Dutch authorities was around 700,000 Euros.

Sources:

- HELCOM, 2002, HELCOM Response Manual - Volume 2
- Bonn Agreement, 1999, Chemical spills at sea: case studies, BONN 99/3/6-E
KOOPS W., State of the art of the 51 chlorine cylinders lost from the M.V. “Sindbad” in December 1979