Within a research centre, a study was conducted to improve output of the phenol oxidation reaction using hydrogen peroxide. During cleaning of the piston reactor with water at the end of the first test, an explosion caused projectiles to be released. One of the technicians positioned adjacent to the pilot installation was seriously injured (temporary deafness due to the explosion). Property damage was minimal (partial destruction of the micro-pilot). The accident was caused by a mechanical malfunction on the phenol line as well as by shutdown of the hydrogen peroxide pump. This shutoff sequence was poorly interpreted by the technician, who manually reactivated the pump. Excess peroxide in the reactor led to a runaway reaction and the eventual explosion.