Tear gas, which is classified as a chemical weapon, is prohibited from being used on soldiers, then why is it being used to scare the crowd?

Protests are going on in West Bengal over the rape-murder case of a doctor. To control the crowd on the streets, Kolkata Police fired tear gas shells and used water cannons. However, this method of controlling the crowd has been quite controversial. Even the Geneva Protocol 1925 and the Chemical Weapons Convention have banned the