Inadvertent mixing of chemicals causes fatalities

The accident occurred in a plant making dyes and a chromate dip for electroplated products. These products were treated in a series of open-topped tanks located in a sub-basement, known as the zinc-plating room, which contained two parallel rows of tanks separated by a grated walkway. A concrete drainage pit lay beneath the walkway. Ventilation in the zinc-plating room was provided by two ceiling exhaust fans, five windows and the door to the room were closed at the time of the accident.The last tank in the series, where the accident occurred, was used for drying parts after they had been electroplated. The tank measured 1.5 x 1.2 x 1.5 metres. The parts were suspended above the tank, and excess zinc cyanide solution dripped into the tank. Waste zinc cyanide was pumped from the tank once each year.On the day before the accident, an industrial cleaning and hauling company pumped the waste from the tank, leaving a layer of zinc cyanide sludge in the bottom. On the day of the accident the night shift leader began preparations to clean the remaining sludge by spraying 1 or 2 gallons of hydrochloric acid into the drying tank.After investigation it was concluded that the night shift leader unknowingly created hydrogen cyanide, a highly toxic compound, by combining sulphuric acid and zinc cyanide, two commonly used industrial chemicals. Hydrogen cyanide acts to block absorption of oxygen by the lungs and can cause death.After adding the sulphuric acid, the night shift leader, who worked alone and wore no respirator, climbed a ladder and descended into the tank. He did not test or ventilate the tank before entering. After several minutes, co-workers saw him struggling to climb out of the tank.Four other workers attempted to help and were quickly overcome. Two were forced back by the vapours. The other two collapsed, one inside the tank and the other with his head hanging over the edge. Fatality.
Lessons
Chemical safety.Ensure that good chemical safety practices are followed in the workplace:
1. Chemicals must be clearly labelled. Labels must be legible and in English. Warnings to be provided in other languages, as necessary.
2. More emphasis must be placed on dangers that can result from combining chemicals. Workers to be trained to recognise and anticipate hazardous chemical reactions.
3. Materials safety data sheets must provide necessary warnings as well as other important information on chemical hazards
Source :LOSS PREVENTION BULLETIN, 122, 9-10