Fire and explosion in a chemicals plant

The process unit affected by the incident was a hydrogenation reaction of phenyl acetyl carbinol with benzyl amine in a solution of isopropyl alcohol and water. The final products were -benzyl derivatives of norephedrine or ephedrine.
The process consisted in two steps: first the hydrogenation by means of a catalyst, followed by the removal of the catalyst and further hydrogenation of the solution. A fire developed when the operator started the first step. The fire was followed by a hydrogen leak and explosion, fed by the release of additional chemical agents.

The consequences were one fatality and three first responders affected by the smoke.

DETAILED EDESCRIPTION OF THE SEQUENCE.
a) Rupture of a glass component belonging to the isopropanol (IPA) supply line. This pipe had been fitted with a bypass featuring steel/glass interface with a double enclosure to protect the glass portion of the pipe. ARIA report does not provide further details on the nature of this component. Due to its failure, liquid isopropyl alcohol was release and formed a pool on the ground. Its evaporation produced a flammable mixture, ignited+D735 by an unknown ignition source. The operator activated the emergency shutdown at the counter and tried to put out the fire with a halon extinguisher. Being unsuccessful in controlling the flames, he decided to exit the building through an emergency exit located very near the fire source. This is when occurred the fatality.
b) Rupture of the hydrogen supply line. This line was above the IPA line. Exposed to strong heat, the line failed at a soldering point releasing hydrogen which ignited causing an explosion followed by a fire.
c) Building’s windows broke at the wall between the workshop and the access gallery, so that the manual shut-off valve cannot be reached. The flame damaged several other shut-off valves and an electrical switch cupboard.
d) A short circuit followed, sending the wrong signal to the pump supplying phenyl acetyl carbinol. The pump started upon this signal pumping the substance through a leaking flange and further feeding the fire.

The INITIATING cause was the rupture of a pipe carrying iso-propanol, its release and ignition and escalation producing the rupture of a hydrogen line and the release of other chemicals.
According to the ARIA report, the isopropanol pipe had been fitted with a bypass featuring steel/glass interface with a double enclosure to protect the glass portion of the pipe. This was the connection which started the event, Against operating the operative instructions, the steel pipe side of the valve had never been closed, triggering a 3.5-bar pressure surge on the glass/metal interface each time the pump started.
Various operative and design deficiencies were found during the investigation, such a lack of safe guards able to prevent escalation and the ill location of the existing ones. The ROOT CAUSE is of an organisational and safety design nature. Part of these deficiencies could be explained by the fact that the plant license did not require its risk assessment and safety design to be assessed by an independent body.

Low pressure hydrogenation unit in a chemical plant.

One operator died and three members of the fire brigade were injured by smoke.
The plant was destroyed . The costs of the properties damage reached several million marks.

Investigation were difficult due to the complete destruction of the plant, including operation procedures and records.

The fire brigade intervened and the fire was contained after 40 minutes, following the closure of hydrogen and phenylacetylcarbinol feed lines.

When the plant was rebuilt sometimes later, the following measures and modifications were adopted:
- Steel pipes were preferred to glass pipes, unless when glass was unavoidable.
- Instead of the manual valve in the hydrogen pipeline, a pneumatic one was installed, which closed automatically when the hydrogen detectors give an alarm.
- Emergency shutdown buttons were installed, able to bring down the whole plant to a safe state.
- Since the main reason for the incident was a valve in the steel pipe left open, an automatic interlock system was installed to prevent an erroneous position of valves. Pumps can start only when all valves are in the correct position according to operating instructions.
- Additional to quarterly safety training, short talks about safety were organised every month.