Explosion and fire in chemical plant

The incident occurred in the hydrogenation unit of a non-further specified chemical plant (SEVESO-classified facility). The hydrogenation unit was probably part of the phenols processing.
Before the occurrance of the event, a growing leak had been discovered in the vicinity of a circulation pump. The pump was switched off and a routine tightening operation of the stuffing box packing was executed.
During the switching on again of the circulation pump, a loss of containment of the circulated fluid occurred, consisting (see eMARS source) in p-tert-butylcyclohexanol p-tert-butylphenol and hydrogen. The fluid ignited, resulting first in an explosion and a subsequent fire.

DETAILS OF THE ACCIDENTAL SEQUENCE
To restart the circulation pump, one employee remained at pump site at while another went to the control room to adjust the pump's flow rate.
When switching on the pump, an abrupt depressurisation via the pump took place. This was only possible because the double shut-off valves on the suction side of the pump were open and the intermediate pressure-reducer was closed. The circulation pump was thus subjected to a system pressure of approximately 300 bar. The pressure sleeve, the stuffing box packing rings, and other associated parts were forced out at this pressure, with consequent release of the fluid.
The employee at the pump was wetted by the released substance and ran to the emergency shower. The employee in the control room noticed smoke coming from the pumping area and activated the off switches for the hydrogen supply valves and the pumps.
Shortly afterwards, there was a loud bang, and following the bang, a fire broke out.
The plant fire department was immediately alerted and extinguished the fire.

INITIATING CAUSE was the re-start of the operation with the wrong set of valves parameters.

ROOT or contributing CAUSE was the lack of training/experience of the workers involved. Although not mentioned by the sources, a root or contributing CAUSE was very probably the absence or inadequacy of operative procedures for the specific action executed.

high pressure hydrogenation reactor, circulation pump, double gate valve

The accident at the restart of the circulation pump, following maintenance works due to leakage.

DESCRIPTION OF THE PROCESS
The hydrogenation unit treated p-tert-butylcyclohexanol ( (CH3)3CC6H10OH) and p-tert-butylphenol ((CH3)3CC6H4OH).

One staff member was injured by the released hot melt, two staff members suffered shock, and another one broke his foot while climbing down a ladder after the detonation.
Costs amount to ca. 1.000.000 EURO inside the premises and 250.000 outside.

During the progress of the run away reactions, measures were taken, such as the shut down of the electrolysers and the circulation pump, which however did not prevent the explosion.

Although not mentioned by the sources, this is a case where an automatic control system could have avoid the wrong choice of valves setting.

(eMARS report)
(1) Supplementary training and instruction of the personnel on the topic "Tightening of stuffing box packings", with a particular focus on the lessons learned from this accident.
(2) Regular safety briefings
(3) Instruction on hazards of working with pressurised equipment.
(4) For a certain time, a supervisor will inspect the accuracy of the tightening operation carried out by the personnel. Afterwards, random inspections of the operation will be carried out by a person in charge.