Biomedical Engineering Reference
In-Depth Information
The sequence of a measurement campaign is such that all instruments to be used
in the campaign are to be checked for plausibility of their results. Results from instru-
ments measuring the same metrics must be intercompared. For the on-site measure-
ments, the measurement staff commonly arrives a day before the actual start of the
measurements to set up the instruments and synchronize the clocks. All instruments
are left running overnight. The overnight measurements have two purposes. On the
one hand they provide background data for a situation in the facility when no one is
working (provided there is no night shift). On the other hand, a quick comparison
of the instruments is used to detect possible damage to the instruments that may
have occurred during their transport. For the measurements, the instrument(s) for
determining the background are placed in a representative background location. If
available, this may be the supply air from the local ventilation system. The instru-
ments for measuring in the near field of the workplace are located near the location,
where particle release is expected. All instruments should sample through a com-
mon inlet, which of course needs to be suitable for the resulting total flow rate, or at
least very close to each other to avoid spatial variations affecting the measurements.
Depending on the conditions in the workplace, the measuring instruments may need
to be placed inside an air conditioned box. The near field measurements should be
accompanied by personal exposure measurements, if appropriate personal samplers
or monitors are available. Prior to the start of the measurements, all instrument flow
rates need to be checked and documented.
The measurements are usually conducted over a full work shift or at least the
length of the considered process. For data evaluation, in principle a similar proce-
dure as in tier 2 is applied. The time series for the particle number concentration
and the geometric mean of the particle size distribution at the workplace must be
presented and every relevant event interpreted. The particle size resolved number
concentration from the size distribution data in the workplace (and if available in the
background) is divided into different particle size fractions which are then further
used for comparison. Only the definition of such harmonized size ranges allows for
a comparison of data gathered by different groups that may even use different types
of instruments. The size ranges to be reported are: Lower size limit (LSL)—100 nm,
100-400 nm, 400 nm-1 µm, and 1-10 μm (only applicable to the size ranges that have
been determined). Since aerosol measuring equipment commonly assumes particles
to be spherical they usually report particle sizes as equivalent diameters of spheres,
where the equivalency depends on the measurement method. All particle size data
reported therefore need to include information on which equivalent diameter is used.
All data from workplace and background measurements are averaged over equal
time steps (e.g., 5 min or 15 min) and the standard deviations calculated. For size
distribution data, this needs to be done for each of the aforementioned size ranges.
The net emission or exposure concentration is calculated according to Equation 11.1
or 11.2, respectively. The workplace or exposure concentration is considered to be
significantly increased if the net concentration is larger than 3 times the standard
deviation of the background concentration. In this case the particle samples are ana-
lyzed for their chemical composition and particle morphology. If the nanomaterial
produced or handled in the workplace is found among the sampled particles, this
proves that indeed the nanomaterial was released into the workplace and caused
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