At 11.57 AM a power failure occurred in a refinery. The supply of electrical power was cut off, as a result of the failure of the main power line during maintenance. Because of this the refinery was almost completely powerless, which led to an emergency shut down of the whole plant. The automatically operated safety systems started working : large quantities of products were dumped in the emergency torch and were burnt off. Safety valves opened and released gasses to the atmosphere. Personnel and people working at the refinery were evacuated and only an emergency staff remained at the plant.
Information at the central operating desk about what was going on in all the components of the plant was sparse. In the first hour after the incident it was not known which safety valves were opened and which products were ventilated into the atmosphere. That information became available bit by bit during the cause of the afternoon.
One of the safety valves that opened released an amount of ca. 70 kg H2S into the atmosphere. The release point is situated at about 40 m above ground level.
After 5 min, the cloud of H2S formed reaches a downwind distance of about 3 km with a concentration valued at nearly 10 ppm 3 m above ground level.
After 20 min the cloud has traveled 14 km and has reached the Netherlands. Concentration levels in the cloud vary between 0.64 ppm at ground level and 0.06 ppm at the top of the cloud at an altitude of about 850 m.
Driven by a wind from the south-south-west at 45 km/hr, the cloud proceeds over the western part of the province of Brabant and after about 70 min has reached the city of Dordrecht, 50 km from the refinery. Concentrations of H2S in the cloud are about 0.06 ppm, still well above the smell detection level .
No warning of the H2S spill was issued, partly due to a lack of information at the plant, partly due to a lack of communication between Belgium emergency services en the Dutch authorities.
A population of about 100.000 people was in the path of the cloud and potentially affected by it. An estimated several hundred people were affected by the H2S and experienced nauseous ness, and respiratory problems. 57 people needed medical care.
However the Dutch emergency services were not prepared to deal with the situation, due to lack of information about the event and its possible consequences. This in turn led to insecurity and a loss of confidence in the capacity of the government to deal with incidents like these.