Ergonomics - Atlas Copco

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coated with dust or damaged by aggressive
dust particles. Inhaled particles will
be transported back and swallowed or
handled by the lymph system. Some will
be encapsulated in the alveoli and reduce
their capability to exchange oxygen and
carbon dioxide. Most of the dust we inhale
is harmless or inert.
Toxic particles
Dust from certain metallic substances such
as manganese, vanadium, cadmium and
beryllium can give rise to severe inflamma-
tion of the lung tissues. This condition is
similar to pneumonia, varying in seriousness
depending on the degree of exposure and the
type of dust involved. Dust from a number of
substances penetrates the wall of the alveo-
lus and is carried out in the lymph system.
These substances include, for instance, lead
and cadmium, which can give rise to symp-
toms of intoxication and which can only be
removed from the body very slowly.
Drop velocity
Particles in aerosols of interest have a very
slow drop velocity. For example, for spheri-
cal particles with the density of water,
1g/cm 2 , drop velocity in air at a temperature
of 20ºC is shown in table 3.14.
The table illustrates that respirable
dust remains floating in the air for a long
time and, as mentioned previously, the
concentration in the operator’s breathing
zone depends heavily on the ventilation of
the work room.
If the operator works in a fettling booth
and air is sucked away from it, this will create
an air flow past the operator. If the velocity ex-
ceeds 0.5 m/s, the air flow will be experienced
as a draught by the operator.
If dust is generated by the process,
clouds of dust with a velocity of higher than
0.5 m/s can move towards the operator and
expose him. The dust clouds can then turn
back into the fettling booth and move past
the operator again. Typical for the scatter of
respirable dust is that the particles follow
the motion of the air in the room.
An efficient general ventilation system will
reduce the amount of particles in the air. An
inefficient system will increase the number of
particles and oil mist during the working day.
To find out the degree of operator exposure,
Dia. (µm) Drop velocity (cm/s)
1 0.003
5 0.07
10 0.3
50 7
100 30
Table 3.14 Drop velocity is highly dependent
on particle size.