In an agro-chemical plant, a mono-product workshop, dedicated to formulating a liquid herbicide, was being used for the salt formation process of another acid. Three days after production had started, market gardeners noted that 40 ha of crops began to wilt. The plant’s management was informed 10 days later. The pollution was caused by weed-killer dusts released into the atmosphere. The frame of the filtration system, part of which was slightly warped, was not hermetic and the filter had not been inspected prior to or during the production period. The workshop’s activity was shut down. External damages were evaluated at 3.5 MF.