Exposure to lead in mineral testing laboratory workers is reduced by a dampening powder
In the gold mining industry, samples are assayed to determine the gold content of mineral ore. One technique, known as fire assay, involves lead oxide (litharge) being added to the sample with a flux. Litharge is normally supplied to the testing laboratory in a powdered form. The sample and litharge are mixed in a cabinet crudely fitted with down-draft ventilation. Then, in a high temperature furnace, the lead combines with the gold, silver and other minerals whilst the rock is burnt away.
Routine blood lead analysis revealed employees were absorbing increasing amounts of lead. Blood lead content ranged from 2.5 – 9.2 µmol/litre. Seven of the fifteen employees at the laboratory recorded more than 3.0 µmol/litre., and two workers were hospitalised. In Victoria, an employee who registers 3.6 µmol/litre must immediately be removed from any task associated with lead. Where any employee registers more than 3.1 µmol/litre action must be taken by the employer to control the lead hazard.
Investigation found that as the litharge was scooped into a paper cup for mixing with the core sample, the powder was being released into the air and was not captured by the down-draft ventilation system. The ventilation system was inadequate as it had not been designed for this specific task, and it consequently kept getting clogged, restricting the airflow.
Operators were therefore potentially inhaling large amounts of litharge dust from the 1200 samples processed per day. Air sampling took place to determine how much dust was being released, and it was found to be excessive.
The supplier of the litharge was contacted, and it was decided that kerosene added as a premix would produce a moist, heavier product which would eliminate the production of dust. The addition of kerosene prevented the distribution of litharge powder into the air.
All workplace surfaces were cleaned to remove any contamination and employees were advised on personal hygiene. Lastly, the laboratory installed a ‘scrubber’ into the furnace extraction system to remove any furnace-generated contaminants. To verify the effectiveness of the controls lead blood level testing was completed after the wetting process was introduced, but before installation of the ‘scrubber’ on the furnace extraction system.
Hierarchy of Controls:
Engineering & administration
- Reduced blood lead levels of laboratory workers below 2.0 µmol/litre.
- There were also some unintended advantages. The kerosene premix litharge was supplied in small drums.
- This reduced the manual handling problems previously experienced with larger litharge drums. There was no significant cost in introducing the solution.