At a chemical plant, fire broke out followed by an explosion due to a defective seal on a tank alongside the polyethylene line, which had been restarted 2 days earlier after cleaning. The extrusion valve malfunction was responsible for increasing temperature and pressure in the upstream reactor. It caused the valve to open, in emptying reactor contents. These temperature and pressure conditions (335°C, 600 bar) stimulated ethylene decomposition, with a portion of the decomposed substances depositing on pipes downstream of the separator. After drainage and rinsing, the extrusion valve was still unable to open correctly. A static decomposition of the substances was initiated between the medium pressure (MP) separator and the exchanger, producing a pressure rise from 180 to 264 bar. This rise wound up circulating substances around the MP returns. The exchanger-induced cooling slowed the decomposition process.
The Head operator ordered the reaction shut down after the extrusion valve had malfunctioned once again. Upon opening this valve, gases hit the hot pipe connecting the separator with the exchanger and triggered a “dynamic” decomposition. The pressure exerted by hot gases crossing the exchanger led the grease bottle rupture disk to burst. Reactor drainage without any back pressure created a pressure drop (from 340 to 100 bar), accompanied by a temperature decrease. Loss of the watertight seal at the level of a reactor bottom joint, due to a minimised autoclave effect (P < 200 bar) and joint retraction, was responsible for a gas leak (decomposing ethylene) inside the reactor bay. The gas cloud ignited, causing an explosion followed by a fire outbreak (on the coolant fluid).
The internal emergency plan was activated. The blaze was brought under control in 20 min by in-house first responders. As a precautionary measure, 23 external fire-fighting vehicles were mobilised to provide backup. One fire-fighter felt faint. The highway fronting the plant was closed to traffic for 15 min due to the presence of smoke (nontoxic according to authorities). The plant manager proposed a number of remedial actions (including improved thermal resistance of joints, a safety device to prevent reactor drainage without back pressure, restricted access to the reactor bay).
