At a fertiliser plant, a raw material hopper (capacity: 42-43 tonnes) feeding the NPK granulation workshop fell, crashing through 2 lower floors and ending its trajectory 10 m below on the concrete floor. The accident caused no human toll, but property damage was significant: a rack of pipes supplying the workshop with ammonia (13 bar, DN50, 25 tonnes/hr), sulphuric acid, phosphoric acid, propane, steam, air, etc. was heavily damaged, yet without any apparent leak.

The pipes were isolated and drained. The manufacturing workshops (nitric acid, calcium ammonium nitrate and NPK fertilizer) were shut down for 2 weeks; operating losses were estimated at €700,000 and property damage at nearly €1 million.

The weakened hopper support during works performed to install spring balances the year before had caused this accident. At the outset, the hopper, support and beam assembly formed a single stable block. When installing the balances, this structure was modified and the resulting loss of stiffness was not specifically studied. Moreover, these works, executed by a subcontractor, did not give rise to any formal acceptance procedure.

Several measures were adopted over the short and medium term: reinforcement by supporting rods and angles of the workshop’s 2 other hoppers prior to any restart; and subsequent modification of existing supports to ensure continued satisfactory operations of the spring balances. A specialist was subcontracted to inspect these modifications. Moreover, the pipes (especially the ammonia line) would potentially be equipped with cut-off devices in order to limit quantities spilled in the event of a pipe break, along with early incident detection devices.