MetFab - Welding Fume Handbook - Flipbook - Page 6
2 Particulate fume
Particles larger than 5 µm are deposited
in the upper respiratory tract. Particles
smaller than 0.1 µm are taken deep into
the lungs during inhalation, but most of
them are removed again by exhalation.
chromium is important because it has a
particularly low exposure limit.
Fume composition is determined mainly
by the composition of the consumable.
This is because around 90% of the fume
originates from the consumable, with
the parent metal making only a small
contribution.
Once the fume composition is known
it is possible to calculate, for each
fume constituent, the total fume
concentration that will maintain that
constituent below its own exposure
limit:
T=100L/C
Manufacturers of welding consumables
must supply information that allows
users to assess the health risks. This
The particles with the highest potential often takes the form of a material
to cause harm are those in the size range safety datasheet (MSDS). In the USA,
0.1-5 µm, which includes welding fume. the MSDS shows the composition of the
These particles penetrate the innermost consumable. In the UK, the MSDS shows
areas of the lungs, the alveoli, and are
the fume composition emitted by the
deposited there.
consumable during welding.
The fume contains all the elements
present in the consumable, but often
in very different proportions. Volatile
components have higher concentrations
in the fume than in the consumable,
and the opposite is true for components
with high melting points.
The welding process also affects
the fume composition. For example,
fume from manual metal arc (MMA)
welding and flux-cored arc welding
(FCAW) contains a high proportion of
components that originate from the
electrode coating or the flux core, and
comparatively little from the filler metal.
Fume from metal inert gas (MIG) and
metal active gas (MAG), in contrast,
contains high concentrations of the
metals being deposited.
Fume from MMA and FCAW usually
contains significant quantities of
hexavalent chromium, while fume
from MIG/MAG does not. Hexavalent
6
where:
T is the total allowable fume
concentration (mg/m³)
L is the exposure limit for a particular
fume constituent (mg/m³)
C is the percentage of that fume
constituent in the total fume.
The constituent giving the lowest value
of T is known as the marker compound.
This approach is used in the UK, France,
Germany and other European countries.
Table 1 shows typical maximum
allowable fume concentrations
calculated using marker compounds.
