| During drossing operations, dross is skimmed to the rim of the kettle and manually shoveled or "spooned" into a container. Mechanical drossing methods, such as vacuum drossing, are used by some secondary lead smelters. Significant levels of lead fume and dust may be released during drossing.
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Click for larger view of mechanical drossing diagram |
| Drossing |
Fig. 1. Manual removal of dross may expose workers to lead dust and fume |
Potential Sources of Exposure:
- Lead dust and fume may be emitted during manual or vacuum dross
removal (Fig. 1).
- Lead dust may be emitted when depositing dross into a waste container.
- Emissions may be released while charging dross to the storage bin via pneumatic conveyance system.
- Lead dust may be spilled and emitted while handling, transporting, and storing dross.
Click for larger view of dross pot hood diagram
Fig. 2. Portable dross hood with flexible duct attachment port
Fig. 3. Mechanical dross vacuum
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Possible Engineering and Work Practice Controls:
- Eliminate or minimize the use of manual drossing. Use automated dross machines where ever
possible (Fig. 2).
Mechanical Drossing Diagram
- Provide an exhaust ventilated barrel or bin in which dross can be deposited before transfer to the storage area.
Dross Hood Diagram
- Provide portable local exhaust ventilation or enclosure to control emissions from dross which is manually deposited in
ladles (Fig. 3).
Moveable Exhaust Hood Diagram
- Provide enclosure and exhaust ventilation for dross storage.
Dross Storage Diagram
- Use a drossing shovel, which allows molten lead to drain prior to removal of dross.
- Use local exhaust ventilation at drossing access locations.
- Do not overfill dross containers.
- Eliminate or minimize the use of a torch for dross cleanup.
- If a torch must be used provide portable local exhaust ventilation or a ventilated torch.
Portable Tool Exhaust Diagram
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| Video Exposure Monitoring: Manual Dross Removal |
Dial up Modem, ISDN
LAN, DSL, T1, T3
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With video exposure monitoring (VEM), worker exposures to lead are monitored and recorded with a direct reading instrument. At the same time, work place activities are recorded on a video tape. The right hand bar indicates changes in total dust concentrations over time.
As the
employee
skims dross
(oxide and
other
impurities)
from the
kettle, the
increasing
red bar
indicates
that the
local
exhaust
ventilation
is
inadequate
to
effectively
capture lead
dust
generated
during
the transfer
of dross
from the
kettle to
the
ventilated
dross
receiving
vessel.
Note: This example illustrates the level and duration of exposure to total
dust and is
used to show how VEM can be
used for determining sources of employee exposure. Other sources of employee lead
exposure can
be
determined
by using VEM sampling
for a full
work shift.
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