Explosions in a reactor used to hydrogenate pharmaceutical intermediates

The accident occurred in a reactor for the hydrogenation of a pharmaceutical intermediate. The operation of the plant was organized in two shifts. Since the hydrogenation reaction was planned for at least 30 hours, it was not possible to complete it during a single shift.
The reaction started at 8:00 a.m. on the day of the accident and at 11:50 p.m., the shift operator closed the system by:
- Shutting off the hydrogen supply to the reactor.
- Closing the valve at the hydrogen cylinder bank.
- Turing off the reactor's agitator
- Isolating the reactor with gaseous hydrogen over the liquid. No nitrogen was used.
The reactor's control panel was showing normal operating temperature and pressure. At approximately midnight, as the new shift was changing in their locker room, they heard a loud explosion coming from the process area. And a fire developed around the reactor.
The area sprinkler system was automatically activated and quenched the fire. A second explosion occurred a few minutes later. A fire with a characteristic black smoke resulted, indicative of a solvent fire.
The building was evacuated. The sprinkler system extinguished this fire. A short while later, the fire services arrived and extinguished small, localised fires on the ground floor around a neighbouring reactor. The building was left vacant for the rest of the night.

The INITIATING cause was the release and ignition of hydrogen from the reactor.
A post-incident investigation concluded that the reaction in the reactor was progressing as planned. The possibility of a run-away reaction could be excluded, also because
the reactor's pressure relief line did not operate, and the bursting disc was found to be intact.
The most probable cause of the incident was a defective agitator. The maintenance record on the agitator showed that it malfunctioned on numerous occasions, but the maintenance had not been sufficient. The agitator could have malfunctioned again allowing a hydrogen leak.
The reactor was in a general process area with plants operating nearby, where an IGNTITION SURCE could easily be found. Some of the electrical plants operating nearby were not explosion proof.
The eMARS report does not provide a description of the system and does explain how the agitator could have enabled the hydrogen release. From the correct measures adopted to avoid the recurrence of the incident, it could be concluded that inadequate operation and safety design were major components of the ROOT CAUSES.

hydrogenation of pharmaceutical intermediate

DESCRIPTION OF THE PROCESS
The process of hydrogenation is carried out by bubbling hydrogen at 35 degrees Celsius into a well stirred mixture of intermediate products dissolved in acetone and presence of a palladium-based catalyst. The hydrogen is fed into the reactor through a 1 cm diameter pipeline from a cylinders bank loacated outside at ground floor level.

MATERIAL LOSS:
The reactor and the connected components were badly distorted; the agitator was blown from its seating and deposited a few metres away; electric cable insulation was charred and the building experienced damages up to 15 metres away; windows glass was shattered and the frames distorted up to 30 metres away. The costs of the damage has been estimated at about 0.4M Euros.

PEOPLE - REMARKS:
No people were injured by the explosion because, when the accident occurred, the operators were changing in their locker room except for an operator that was trapped in the mill room weighing finished product. He could not exit by the process area and had to exit through a hatch on the floor, jump onto a rotary dryer below and climb down to the ground floor.

The area sprinkler system was automatically activated following the first explosion and fire around reactor 6 and quenched the fire. A second explosion then occurred a few minutes later followed by a fire with a characteristic black smoke resulted, indicative of a solvent fire. The sprinkler system again extinguished this fire. A short while later, the fire services (counting 15 fire fighters)arrived and put out small localized fires on the ground floor around Reactor 6. The building was left vacant for the rest of the night.

No off-site emergency measures were necessary. No emergency measures are still necessary, neither on-site nor off-site

After this accident, the following measures were established:
1- to carry out hydrogenation in a separate dedicated process area with electrical equipment suitable for use with hydrogen;
2- to provide adequate alarms to warn when a hydrogen leak could occur. The Company was also required to:
3- to implement a more extensive preventive maintenance system;
4- to install appropriate pressure relief devices to ensure that emissions do not vent into the process area;
5- to review procedures to ensure that processes which have to be left unattended overnight are left in a safe state;
6- to provide nitrogen purging in any reactor containing highly flammable solvents which have to be left unattended overnight.