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Lasers are now an essential tool
in industry for cutting, marking, engraving and welding
a vast range of materials. Metals are the most commonly
worked substrate but organic materials (plastics, paper,
wood) are catching up fast.
In virtually all the above operations
some form of fume is given off as the laser thermally decomposes
the substrate to a greater or lesser degree. This fume is
a mixture of particulate and gaseous matter.
Fume from materials such as metals
and glass is mainly particulate, the majority of which is
less than 1µ (micron) in diameter.
Organic materials, particularly plastics,
produce much more complex fumes which are investigated below.
The particle size distribution of
the airborne particles is shown on graph 1 (above) and with
small variations relates to the majority of polymers. Most
of the particles are spherical and roughly 90% by weight
are less than 1µ in diameter. These particles fall
within the respirable range and need to be removed from
the working environment to prevent bronchal or lung damage.
The gaseous organic compounds produced
are known as Volatile Organic Compounds, VOC's.
The VOC's produced are a mixture
of the following:
| Aliphatic
hydrocarbons: |
alkane,
alkene |
| Aromatic
hydrocarbons: |
benzene,
toluene, xylene |
| Aldehyde: |
formaldehyde |
| Polycyclic
aromatic hydrocarbons: |
benzo(a)pyrene |
Additionally some materials have
other specific groups e.g. PVC polymers generate HCl, 2
component epoxy polymers yield amines and PET generates
THF.
A considerable number of the above
have Occupational exposure limits set for them and these
are detailed in the Operator health section. (Link). Obviously,
as with the particulate element these gases need removing
from the workplace.
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