se

The concentration of dust in the air to which a worker is exposed
will vary, depending upon the nature of the operation and upon the type of
work performed by the operator and the position of the operator relative to
the source of dust. The amount of the dust inhaled by a worker can vary
daily, seasonally and with the weather. In order to obtain representative
samples of workers' exposures it is necessary to collect samples under varying
conditions. The percentage of working time spent on different tasks will
affect the concentration of dust the worker inhales since the different

tasks usually result in exposure to different concentrations.

The concentration of any air contaminant resulting from an
industrial operation also varies with time. Therefore, a longer sampling

time will better approximate the actual average.
3H TEN MINUTE SAMPLING PERIOD

The 10 minute sampling period is to provide an initial assessment
of the atmosphere in working environments and it is the agreed standard period
of time to be used in routine primary sampliag for the purpose of assessing
concentrations of airborne asbestos dust. A 10 minute sampling is defined.
as a continuous sample which is collected over a period of 10 minutes.
"Continuous" means that the flow of sample air through the sampling apparatus
is at a constant rate. This is the British method. The U.S. method calls for

a minimum sampling time of 15 minutes.
4. CONTINUOUS SAMPLING (STATIC SAMPLERS )

This is where a personal sampler is placed in a fixed location
at the same height as an operator's breathing zone and a continuous sample
is taken across a period of time. This may be a 10 minute to an 8 hour
sample.

Si CONTINUOUS SAMPLING (MOBILE SAMPLERS)

This is where an employee carries a personal sampler with the

sample head in his breathing zone traversing the designated area and a-