Explosion in the process reactor of a silicon production plant

The event occurred during the production of a silicon oil- and additive-based waterproofing agent. A junior technician (hired 6 months back), recently assigned to this post, was left during the night without supervision to manage a process modified very recently and executed only for the second time.
The technician loaded first 800 kg of oil into the tank at first floor, started heating the reactor, and descended to the ground floor to pump the reagent. When going up to the second floor to fill a tank with water, he observed a kind of fog escaping from the tank.
An explosion of the tank followed, caused by the formation of hydrogen and perhaps also sodium hydride (NaH) from the decomposition of the silicon oil after the abrupt and uncontrolled addition of an extremely basic alcoholate (wrong pH control).

The fire that ensued consumed 500 tonnes of chemicals (mainly alcohols), spread to significant part of the site (7,000 m2) and resulted in a huge cloud of smoke.

The technician was severely injured, 2 responders as well, and 15 people were intoxicated by CO during the emergency.

INITIATING cause was a wrong sequence of action in loading the feedstocks into a reactor. In the process instructions, the order of addition of reactants was not specified.

ROOT CAUSES were a ill-defined procedure, and insufficient training of personnel.
Adding to this, was the unavailability of detailed and updated inventory of the chemicals stored on site and an inadequate emergency plan.

chemical reactor

The production process had been modified very recently and at the moment of the incident, it had ben executed only for the second time .

The plant was an organic chemical industry for the production of various chemicals for the textile and the plastic materials industries. It employed 150 people, was built in 1958 and in 1985 was provided of a new polymers production plant using benzene as solvent. It produced about 800 different chemical products.

1 technician severely injured, 2 fire-fighters injured and 15 intoxicated by CO.
Material damage and operating losses of the company stood at 45 million of Francs (MF) and 8 MF respectively.

Analysis of the air revealed low levels of CO and NOx.

Two rivers were polluted for several km, wiping out all traces of plant and animal life: 20 tonnes of fishes, aquatic and terrestrial mammals were destroyed.
Due to the high phenol index measured in one of the rivers, water supply was stopped for 3 days with a ban on human consumption for 8 days. Drinking water supply was arranged for 10 days.

The chairman of the company was given a 1-year suspended sentence and fined 120,000 F (French Francs, 18000 Euros) while the plant manager received a 6-month suspended sentence and was fined 60,000 F (9000 Euros).
The damages to be paid to the civil party stood at 800,000 F (120000 Euros).

3:00 The alarm was given by an habitant of the zone.
3:20 Intervention of the first professional fire brigade, not effective in fighting a fire of 500 t of different chemical products, including a majority of alcohols.
4:00 - Evacuation of 200 habitants because the fire extended to a surface of 3 000 m², intensified and generated a dark and toxic fume nitrogen oxides, ammonia, etc.)
The high temperature helped the decomposition of the stored chemicals so that the concentrations of HCN, CO and halogens remained under control, and only CO et NOx were detected.
7:00 - situation under control.

The absence of retention devices, unused pipes and malfunctioning of the internal waste water treatment plant led to the disposal of the fire water (cyanide compounds, pentachlorophenols, etc.) into the neighbouring river, which transported the polluted water into other rivers. .

The inquiry discovered several safety management shortcomings:
1. Measures to prevent recurrence: violation of the existing safety rules.
2. Measures to mitigate consequences: total lack of an internal emergency plan.
3. Emergency management: too few personal protection equipment; incapacity to reach quickly information on the existing chemical risks for the surrounding, and lack of quick quantitative assessment of atmospheric pollutions.