In a fertilizer manufacturing plant, a leak occurred in one of the ammonia (NH3) loading stations. The leak is detected by an NH3 sensor positioned on the fence between the site and a refinery that triggered the alarms. Upon reception of the alarm, workers operated emergency buttons that stopped the NH3 loading pumps. The site’s internal emergency plan was activated ; the neighbouring refinery also triggered its emergency plan in order to confine its 300 employees. The end of the alert was given 1 h later; the amount of NH3 released was estimated at 300 kg. The maximum NH3 concentration measured at the property boundary was 135 ppm 10 min after activation of the alert.

Three days earlier, flow problems were encountered on the drain valve on the liquid NH3 intake line at the loading platform. The circuits had been isolated for maintenance. The latter once completed, the supervisor asked the operator to re-pressurize the loading dock to do a test operation of the valve before signing the end of work. Without written instructions for resuming loading station operations, the operator forgot to close the drain valve before restarting the operating line (13 bar, 0 ° C), leading to a leak via the ammonia drain collection system.

To lower the probability of such an accident recurring, various remedial actions were implemented: drafting of an operating guideline for both service start-up and isolation of the installation (loading station), technician training, identification of drain valve locations. The operator studied the installations of systems to better visualize the position of the drain valves and detect leaks at the NH3 purges collection system. Finally, the operator installed an automatic valve upstream of the loading pumps.