MetFab - Welding Fume Handbook - Flipbook - Page 40
11 Control
Regulations require that exposure to welding fume and
pollutant gases must be prevented, or where this is not
reasonably practicable, adequately controlled. The hierarchy
of decisions is therefore:
Can exposure be prevented?
If exposure cannot be prevented, can it be controlled using
methods other than respiratory protective equipment (RPE)?
If RPE is required, what kind?
Once a decision has been made to
complete a joint using welding,
complete prevention of exposure
becomes difficult. However, it may be
possible to reduce exposure. One option
is to choose a shielding gas, and perhaps
even a welding process, that generates
lower emissions. Another is for the
welder to position himself correctly,
with his head out of the fume and
paying attention to the direction of any
draught.
LEV systems are frequently used on
large fabrications that are not easily
moved. High-volume / low-velocity
systems with large-diameter trunking
and flanged hoods are preferred.
Extracted benches typically take the
form of open-fronted boxes, with air
extracted through slots or grilles in the
back. The workpiece is placed inside the
box for welding, and the fume is carried
away from the welder in the extracted
air. Extracted benches are suitable for
In practice, adequate control of exposure small components that can be handled
can usually be achieved only with the
manually.
help of ventilation or extraction. The
Extracted booths are similar to
choice of technique depends on the
extracted benches, but much larger.
circumstances, but the aim is to capture They are used for workpieces that are
the fume at source. This protects not
too large to fit into an extracted bench
only the welder but also other workers. but that are relatively easy to move.
There are four main methods of
removing fume at source: local exhaust
ventilation, extracted benches, extracted
booths and "on gun" extraction.
Local exhaust ventilation (LEV) is
the most common form of extraction
for welding. It may take the form of a
workshop system with fixed ducting,
enabling extraction to be applied at any
point in the workshop, or mobile units
with their own filtration systems.
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