At an agrochemical plant, an explosion occurred near a drained hydrofluoric acid tank as 4 employees were welding on adjacent pipelines. One of the technicians died as a result of his burns, while the other 3 sustained injuries. According to the operator, air pollution measurements recorded around the plant did not indicate the presence of any toxic products, and moreover the impacts on both the environment and local residents would be minimal. An investigation was launched to determine this accident’s causes. The presence of hydrogen might have been the source. Except for the unit already shut down for maintenance, plant activity was not interrupted.