In addition, you can reduce the hazard level
if you are able to switch materials to an
alternative that is less toxic, or to one that
does not create as much vapour or dust.
One of the most common ways in which you
can control fumes and dust is to extract it
from the environment using a Local Exhaust
Ventilation system (LEV) which uses filters or
a duct to atmosphere system - depending
upon the type and level of fume problem.
REMOVING FUMES AND DUSTS
FROM THE ENVIRONMENT
The vast majority of LEV systems are ‘recirc’
or recirculation extractors. Recirculation
extractors are devices that pass air through
a filter to trap the fumes and dust and pass
the clean air back into the local environment
near the source. These extractors can be
portable, with the advantage that they can
be moved to the area where there is the
greatest need for fume and dust removal.
The other main type of extraction system
is known as a ‘vented to atmosphere’
system, but these are mainly targeted at
fume extraction rather than dusts, unless a
degree of filtration is present first. These are
more traditional and involve a combination
of ductwork, extraction hoods, and filters
connected to a fan in the wall or roof and an
exhaust that releases air outside the building
or to an area away from the initial source.
These systems are predominantly utilized for
hazardous fumes but can also extract small
volumes of fine dusts when necessary.
Particulates (Dusts and Smoke) can be
filtered in a variety of ways and there are
many grades of particulate filter. The most
effective type and probably the most widely
known is a High Efficiency Particulate
Arrestor (HEPA). These filters are very fine and
often remove higher than 99.99% of particles
down to 0.3 microns. Other types of particle
filters include F grade or EU (Eurovent) grade
filters, dust bag filters, course dust filters, M
Class filters, and inline dust filters.
Vapours or odours will pass right through a
particle filter (even HEPA filters), so carbon
filters are often used to adsorb these
vapours. Not all carbons are suitable for
every type of vapour however so the type of
fume has to be matched to the right type of
carbon.
Activated carbon is the universal adsorbent
and will filter “some of almost any vapour”.
Gases that are removed by activated carbon
filter systems include:
• Organic Compounds: Acids, Alcohols,
Aldehydes
• Chlorinated Hydrocarbons: Esters, Ethers,
Ketones, Mercaptans, Amines
• Inorganic Compounds: Halogen Acids,
Halogens, Sulphuric Acid, Sulphur Dioxide,
Phosgene
• Odours: Human, Animals, Food, Waste
Processes, Cooking
Special carbon additives can be mixed with
activated carbon to make it more effective at
removing certain types of chemicals.
For more information,
visit www.vodex.co.uk.
Issue 38 PECM
83