A post claiming that South Korean police use purple dye at protests to later identify and arrest protesters has been shared over 19,000 times on Facebook.
South Korean police have previously used dye at protests to identify and arrest protesters, (although this was yellow or orange-ish dye, not purple.) But factcheckers at Seoul National University told Full fact that dye cannons have not appeared at protests for many years now.
The purple dye example is actually more commonly associated with anti-apartheid protests in South Africa. Water cannons shooting out the purple dye gave the “Purple Rain” protest in Cape Town in 1989 its name.
Dye cannons have been seen in Uganda, Egypt, and India, and more recently police in Hong Kong used them. As stated in the post, their purpose is to deter protestors as well as to mark them out for later identification.
In South Korea, use of a water cannon at a protest led to the death of a farmer during a protest in 2015. The water cannons contained tear gas. It was reported in 2017 that the country’s police force would pause the use of cannons at protests, and in April of this year, in reference to the 2015 death, it was ruled that the use of water cannons in this manner was unconstitutional.
Water cannons have never been deployed in the UK outside of Northern Ireland. In 2018, cannons bought for London after the 2011 riots were sold for scrap. In the UK, attending a protest is not an arrestable offence, however people can be arrested for their behaviour at protests for crimes such as public order offences.