MetFab - Welding Fume Handbook - Flipbook - Page 41
11 Control
On-gun extraction can be used with
continuous wire welding processes
(MIG/MAG and FCAW). This has
the advantage that the extraction
point is always close to the source
of fume. Disadvantages include the
increased weight of the gun, reduced
manoeuvrability for the welder, and
reduced extraction efficiency when
welding in positions other than flat.
Correct adjustment of the inlet is
difficult but important. If the inlet is too
close to the arc, it removes the shielding
gas and weld porosity occurs.
If it is too far away, it does not extract
the fume properly.
To reduce background levels of fume in
the workshop, general ventilation may
also be needed. This is not a substitute
for proper local ventilation. There are
two basic types of general ventilation:
dilution ventilation and displacement
ventilation.
RPE is necessary. RPE protects only the
person wearing it, so it must be used in
addition to, not instead of, extraction.
Types of RPE range from simple orinasal respirators for low levels of
particulate fume to air-fed helmets
for use in situations where there may
also be a shortage of oxygen. Take
great care when choosing RPE. Consult
both manufacturers and the HSE guide
Respiratory protective equipment:
A practical guide for users (www.
hsebooks.co.uk).
When extraction equipment or RPE is
required to control emissions, employers
must ensure that it is properly used and
maintained, with records kept for five
years. Employees must make proper use
of the equipment provided and report
any faults to the employer.
Dilution ventilation directs air towards
the source of the fume, mixing it
with the workshop atmosphere and
ultimately removing it using extraction
fans. Dilution ventilation is not very
effective and should be restricted to
situations where the amount of fume is
small.
Displacement ventilation introduces
clean air into the workshop near floor
level and extracts fume-laden air at
ceiling level. This technique is suited
to high workshops containing a large
number of small sources of fume.
If ventilation or extraction cannot
provide adequate control on its own,
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