In a chemical depot, sodium hypochlorite and formic acid were accidentally mixed while transferring a product from a tanker truck to a fixed tank. Chlorine leaked from the vent of the tank until the valves were closed by the technicians. Ten people were poisoned (truck driver, depot staff and subcontractors) and hospitalised. A third party company analysed the conditions under which the truck was taken for delivery as well as the conditions for the treatment of the polluted tank.