The accident occurred at a distillate dewaxing Unit (MDDW) of the refinery, during the operation of regeneration of the catalyst. To perform this operation, both temperature and pressure have to be increased. After approximately six hours after having reached the correct regeneration conditions, the 10 inches pipe at the bottom to one of the two reactor experienced a guillotine break, and hot gas was released from both ends. The gas released consisted of 81% of hydrogen, 9.5% of methane and some light hydrocarbons. It rapidly ignited (0.7 sec), causing an explosion.

Fire in chemical plant (Seveso-classified)The fire developed at the top of the flare stack of a during a violent thunderstorm.The flare stack is used to discharge hydrogen produced by the restarting of chlorine electrolysis cells. The fire was ignited despite steam and nitrogen had specifically were injected to prevent it from occurring. The sites firefighters cooled the flare stack while the technicians turned off the electrolysis cells to cut off the hydrogen feeding the flames.

A hydrogen fire occurred in a nuclear power plant outside the controlled area. The leaking point was on a pipe system of the distribution circuit of the gas network (6 bar nominal working pressure). The specific location was a joint on the fire-protection cupboard containing the hydrogen cylinders. The fire started during a repairing intervention on a cupboard nearby, performed by a sub-contractor using a hot surface welding equipment. Internal emergency services isolated and depressurized the pipes, and extinguished the flame.

First an explosion and then a fire occurred on the condensate piping of an chlorine electrolysis plant (SEVESO upper tiers). Flames escape from the end of the pipe and spill into a 75 m open sky tank, containing the electrolysis products (water, HCL, NaOH, Na). According to the ARIA report, (see source) a maintenance operation was ongoing on the HCl furnace located nearby. Investigations conducted by the operator identified a design defect as the cause of the incident. The overflow of the guard hydrogen hydraulic system was wrongly connected to the condensate piping.

The event early on a Saturday morning, when the plant was thus practically empty. Nevertheless, the chronology of the accident can be reconstructed from the testimonies of the few operators who were present at the time:Phase 1: Gas leak - Loud whistling from the hydrogen storage facility could be heard , lasting 20 to 40 seconds.Phase 2: Explosion - The released hydrogen cloud ignites. A very bright, red-orange fireball measuring 15 to 20 m in diameter was visible for 3 minutes. Witnesses in a common room, located 100 m away from the pit, felt the shock wave and the heat from the blast.

Three workers were working in the sulfur recovery unit (SRU), trying to restore the hydrogen flow. The workers were trying to isolate the cause of a flow problem: hydrogen was entering the regulators at 200 psi (14 bar), but the pressure was dropping to 18 to 20 psi (approximately 1.3 bar) after the passed through the various components of the unit. They closed a valve preceding the regulators and vented the bleed manifold before removing a flange located beyond the valve. One of the worker then re-opened the closed valve to check the flow.

An employee was preparing a batch of glycol stearate emulsifier in a vessel. Upon completion of product, the quality control lab reported that the pH was too high and the product needed to be bleached. When the employee reached the step of adding the sodium borohydride, he decided to relieve the pressure in the vessel by opening the valve used to introduce sodium chlorite. As he opened the valve, sodium chlorite (liquid) residue discharged, spraying the grating and the plastic bucket which contained sodium borohydride.

Gaseous hydrogen leaked from an oil pump part of the filling and conditioning system in a industrial gases production plant. The released hydrogen ignited and exploded. The cause has been a human error: an operator turned gave a valve a turn, connecting containers, which were not empty, with the pump. The hydrogen release occurred in an open space under an awning. This caused the flammable mixture to explode producing a fireball of 10 m of diameter. 2 workers were injured but the material damage was limited to a door and a small room.

Fire and explosion in a chemicals plantThe process unit affected by the incident was a two-step production, consisting of i) hydrogenation of phenyl acetyl carbinol with benzyl amine in a isopropyl alcohol/water mixture by means of a catalyst ii) removal of the catalyst and further hydrogenation of the solution.At the moment of the incident the operator was starting the first step of the hydrogenation. A first fire, detected by the automatic fire alarm, was followed by a hydrogen leak and explosion, fed by the release of additional chemical agents.

The incident occurred in the hydrogenation Unit of a non-further specified chemical plant. Before the occurring 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, an abrupt depressurization via the pump took place. This was due to the fact that double gate valve on the pump's suction side was open, while the valve of the intermediate pressure reducer was closed.