The working group aimed at a harmonized approach for exposure measurement and exposure assessment. The outcome is pragmatic and widely usable. This tiered approach can be widely used by small and medium sized enterprises as well as large chemical companies with global business operations.
The main findings of the working group can be
summarized as follows:
Safe work places where ENMs are produced or pro
cessed can be achieved, using existing technology,
and which conforms with best industrial hygiene practices.
Existing substance-specific, binding, health based
OELs must be complied with and are not subject of or
overridden by the current approach.
Exposure measurement of nanoscale aerosols released
from ENMs in the work-place is possible and
exposure assessment methodologies exist. However,
methodologies are not yet standardized and more difficult
to apply as in routine operations, e.g. gravimetric
dust measurements according to DIN EN 481.
Equipment required for measurement of exposure to
nanoscale aerosols released from ENMs is sophisticated
and the results produced, e.g., total particle num
ber concentration, have no direct correlation to the
chemical identity. Calibration of equipment is still a
challenge and validation using round robin testing,
which is typically correlated with SMPS results, is difficult
as no commonly accepted reference method is
At the moment, for a practitioner, a tiered approach
to exposure assessment appears to be the most ap
propriate strategy. This approach is split into 3 tiers. In
the first step (Tier 1) information is gathered according
to established industrial hygiene practices. In the next
tier (Tier 2) a basic exposure assessment using a limi
ted set of easy-to-use equipment is conducted, where
as in the highest tier 6 (Tier 3) the latest state-of-theart
measurement technology is employed to assess the
potential for workplace exposure to nanoscale aerosols
released from ENMs if required.
Existing legally binding OELs, e.g. synthetic amor
phous silica [TRGS 900: EC No. 231-545-4], carbon
black [ACGIH], etc., have to be complied with. Where
no such substance-specific, binding, health-based OEL
values for ENMs exist, the tiered approach is using 3
criteria for the assessment of the data:
1) Interference value exceeded for nanoscale aerosols
released from ENMs.
2) Significant increase over aerosol background
level in the workplace air.
3) Chemical identity of the nano-objects and their nanoscale
aggregates and agglomerates detected in the
The application of the decision logic leads in total to
7 different cases (Case A – G), which may guide the risk
management decisions of the practitioner.
This step-by-step approach may need to be revisited
as soon as new scientific findings are available (especially
on binding, health-based occupational exposure
limit values). The presented exposure assessment strategy
of nanoscale aerosols released from ENMs in the
workplace may serve as a starting point for further