Push-pull principle improves vapour extraction in electroplating
In an aircraft, hard chrome electroplating is used to protect various components from corrosion. During the electroplating processing, large quantities of hydrogen and various chromates (including chromium VI compounds) are released into a worker’s breathing zone. Initially a local exhaust ventilation system (LEV) was installed to remove vapour from the surface of the electroplating solution to an extraction system located at the rear of the tank.
Personal monitoring in the breathing zone of employees performing this activity produced readings of 0.11 mg/cubic metre. The recommended exposure standard for water soluble chromium VI compounds is 0.05 mg / cubic metre (1991).
Consultation between the health and safety representative and the supervisor resulted in the plating tank being converted from an LEV system with rear extraction (“pull”) to a “push-pull” LEV system. Vapours are ‘pushed’ away from the operator towards the direction of the rear mounted extraction system. This airborne contaminant control strategy effectively reduced the measured chromium VI compounds in a worker’s breathing zone to 0.03 mg/cubic metre.
It should be noted that “push-pull” local exhaust ventilation systems require constant monitoring to ensure their efficiency. Several factors may influence their operation.
- Cross-draft airflow
- ‘Push’ and ‘pull’ airflow balance
- Airflow diversion (e.g. due to objects being passed through the airflow)
- Poor maintenance of the system; and
- Nozzle size on the blower unit
In short the fabrication and maintenance of a ‘push-pull’ extraction system requires attention to detail.
Hierarchy of Controls:
- The workplace was made healthier and safer for employees.
- A 0.08 mg/cubic metre reduction in water soluble chromium VI compound fumes was achieved.