CEN/TS 18117:2025

SLOVENSKI STANDARD
01-april-2025
Izpostavljenost na delovnem mestu - Določanje in karakterizacija lebdečih
nanopredmetov ter njihovih agregatov in aglomeratov (NOAA) z elektronsko
mikroskopijo - Pravila za vzorčenje in analizo
Workplace exposure - Detection and characterization of airborne NOAA using electron
microscopy - Rules for sampling and analysis
Exposition am Arbeitsplatz - Nachweis und Charakterisierung von luftgetragenen NOAA
durch Elektronenmikroskopie - Regeln für Probenahme und Analyse
Exposition sur le lieu de travail - Détection et caractérisation des NOAA en suspension
dans l'air par microscopie électronique - Règles d'échantillonnage et d'analyse
Ta slovenski standard je istoveten z: CEN/TS 18117:2025
ICS:
13.040.30 Kakovost zraka na delovnem Workplace atmospheres
mestu
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEN/TS 18117
TECHNICAL SPECIFICATION
SPÉCIFICATION TECHNIQUE
February 2025
TECHNISCHE SPEZIFIKATION
ICS 13.040.30
English Version
Workplace exposure - Detection and characterization of
airborne NOAA using electron microscopy - Rules for
sampling and analysis
Exposition sur le lieu de travail - Détection et Exposition am Arbeitsplatz - Nachweis und
caractérisation des NOAA en suspension dans l'air par Charakterisierung von luftgetragenen NOAA durch
microscopie électronique - Règles d'échantillonnage et Elektronenmikroskopie - Regeln für Probenahme und
d'analyse Analyse
This Technical Specification (CEN/TS) was approved by CEN on 15 December 2024 for provisional application.

The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to
submit their comments, particularly on the question whether the CEN/TS can be converted into a European Standard.

CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS
available promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in
parallel to the CEN/TS) until the final decision about the possible conversion of the CEN/TS into an EN is reached.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TS 18117:2025 E
worldwide for CEN national Members.

Contents Page
European foreword. 3
Introduction . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Abbreviations . 9
5 Procedure . 10
6 Sampling . 13
7 Analysis . 15
8 Calculation of results . 31
9 Test report . 35
Annex A (informative) Apparatus and materials . 36
Annex B (informative) Round Robin on LAR-particles . 45
Annex C (informative) Round Robin of Fibres . 62
Annex D (informative) Round Robin of sampling efficiencies . 87
Annex E (informative) Examples of objects typically found on aerosol samples from workplaces
and how to characterize and count them . 102
Annex F (informative) Value tables . 117
Bibliography . 121

European foreword
This document (CEN/TS 18117:2025) has been prepared by Technical Committee CEN/TC 137 “Assessment
of workplace exposure to chemical and biological agents”, the secretariat of which is held by DIN.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document has been prepared under a standardization request addressed to CEN by the European
Commission.
Any feedback and questions on this document should be directed to the users’ national standards body. A
complete listing of these bodies can be found on the CEN website.
According to the CEN/CENELEC Internal Regulations, the national standards organisations of the following
countries are bound to announce this Technical Specification: Austria, Belgium, Bulgaria, Croatia, Cyprus,
Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North Macedonia,
Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the United Kingdom.
Introduction
Methods to assess exposure to nano-objects and their agglomerates and aggregates (NOAA) in the workplace
are only partially standardized, for example the metrics to be used for exposure assessment, the tiered
approach to collect exposure measurements, the way to operate the condensation particle counter (CPC),
approach to assess dermal exposure to nanomaterials. In addition, many guidelines are rather outdated by
not outlining the requirements to identify nanoforms, as the technical standards by the time of their
formulation were not sufficient to detect nanoscale dimensions or nanoforms were not regarded of special
interest. To determine workplace exposure to particulate matter, gravimetric methods were established that
weigh the collected dust to determine mass load and a respective mass concentration for a compliance test
against occupational exposure limit values (OELV). However, those methods are insensitive towards the
particle size and in case only the fraction of NOAA needs to be determined, electron microscopy (EM) is a
necessary supplemental technique for the identification and physical characterization of NOAA, including
nanofibres (e.g. carbon nanotubes (CNTs)), nanoplates (e.g. graphene) and nanoparticles. With the help of
energy dispersive X-ray spectroscopy (EDS/EDX) as an add-on to EM, also chemical identification of NOAA
can be accomplished. EM methods referred to in this document include scanning electron microscopy (SEM)
and transmission electron microscopy (TEM), which are two different techniques with different capabilities.
Fibres are of special interest, since their potential hazard can arise from their length and diameter, calling for
geometrical characterization of high aspect ratio particles found in the collected workplace aerosol with EM
techniques. In fact, the WHO established a fibre counting convention that identifies fibres in case
length > 5 µm, diameter < 3 µm and aspect ratio > 3 (WHO-fibres). Legal OELV for fibres are based on this
counting convention. However, the diameter had also a lower limit of 200 nm, accounting for the resolution
limit of phase contrast microscopy commonly used in the time when these Standards for asbestos exposure
assessment were written. Consequently, nanofibres would not be detected and counted. However, the past 20
years of nanotoxicological research attributed asbestos-like hazard potential to some nanofibres like carbon
nanotubes, which in parallel became increasingly used at workplaces. Therefore, newer guidelines and
standards for fibre workplace exposure assessment decreased or cut the lower diameter limit and
implemented the application of EM methods. Nanoparticles of non-fibrous materials indicate a higher toxicity
in comparison to micro sized particles due to the higher chemically active surface to mass ratio.
Even though no NOAA-specific legal OELV exist by the time of the formulation of this document, so-called
health-based nano reference values (HNRVs) for occupational exposure have been proposed for some
engineered nanomaterials (ENM). Especially in mixed dust environments, a quantitative analysis with EM
would have great added value for respective compliance tests, because of the possibility to distinguish
different morphological particle types, i.e. nanofibres versus other shapes. Chemical analysis included in the
EM methodology would allow for a complete identification of ENM against a complex particle background.
Thus, the application of EM analyses for assessing the actual type of exposure can be envisaged for all
workplaces dealing with nano-objects, e.g. producers of nanoparticles and also companies subsequently
employing nanoparticles in different products. Furthermore, due to the production of unwanted nano-objects
during processes including heat or mechanical treatments an assessment of the possible exposure might be
favourable. The EM analysis can unambiguously identify the nature and chemical identity of the nano-objects
and thus contribute to a complete workplace exposure assessment.
EM analysis relies on aerosol collection methods to produce samples that comprise particles that can firstly
be visualized and secondly characterized. Both prerequisites call for aerosol collection protocols specially
adjusted for the technical boundary conditions of the used EM as well as the analytical procedure that includes
image acquisition and subsequent particle counting as well as the measurement of selected particle
parameters.
For aerosol collection, several types of samplers exist, based on different collection principles (e.g. filtration,
impaction, electrostatic or thermophoretic precipitation) and collecting different size ranges of particles.
However, the analysis of NOAA by EM has strict requirements for samples, which leads to the use of specific
methods of sample collection and preparation. Despite the different requirements of SEM and TEM that affect
the way samples are collected and prepared for analysis, it is necessary for both techniques to collect
homogeneous deposits, with a minimum of overlapping of the particles. Furthermore, the particles on the
collection medium should be in the same particle size range to which workers are potentially exposed to, from
single nano-objects to micron sized agglomerates and aggregates.
EM analysis also comes with strict requirements in particular in the context of testing the workplace aerosol
against a specific OELV, which are specific to particle types. Hence the technicalities of the analysis would be
adjusted to be optimal to identify, count and characterize the chosen particle type. In addition, the statistical
requirements in order to be confident towards the compliance test result call for strict rules. In turn, general
characterization of the workplace atmosphere to “get an idea” of its particle type composition would call for
boundary conditions allowing to visualize, count and analyse all kinds of nano-objects on the sample but
without being bound to strict statistical requirements. Generally, applicable protocols for EM analysis of
workplace samples should therefore set the rules for image acquisition, particle identification, counting and
characterization based on the analytical aim. A modular formulation of an EM protocol might enable this
strategy.
A set of validated sampling devices and collection media with experimentally determined collection and
sampling efficiencies is presented in this document, together with a set of validated protocols and guidelines
for the characterization and quantification of airborne nanoparticles, nanofibres and nanoplatelets and their
agglomerates and aggregates using EM methods.
The methodology could be implemented as a higher tier step in an occupational exposure assessment strategy
for NOAA. Results from this analysis can be used to compare to health-based limit values, as they become
available and to understand potential health risks of workers.
NOTE Examples of direct reading instruments are CPC, SMPS, ELPI; these instruments are listed in the OECD
guideline [1].
1 Scope
This document provides rules for workplace sampling and the sample analysis for the determination and
characterization of airborne NOAA for electron microscopy and includes:
— the choice of appropriate samplers and their use for the determination and characterization (e.g.
classification of structures and morphology) of airborne NOAA using electron microscopic methods (SEM
and (S)TEM);
— counting rules and criteria for the determination and characterization (e.g. classification of structures,
chemical composition and morphology) of airborne NOAA using electron microscopic methods (SEM and
(S)TEM), especially for nanofibres and platelets.
This document is based on extensive laboratory tests for airborne NOAA, in particular those released during
the handling of engineered nanomaterials.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
EN 482, Workplace exposure - Procedures for the determination of the concentration of chemical agents - Basic
performance requirements
EN 689, Workplace exposure — Measurement of exposure by inhalation to chemical agents — Strategy for
testing compliance with occupational exposure limit values
EN 1540, Workplace exposure — Terminology
EN 17058, Workplace exposure - Assessment of exposure by inhalation of nano-objects and their aggregates and
agglomerates
EN ISO 13137, Workplace atmospheres - Pumps for personal sampling of chemical and biological agents -
Requirements and test methods (ISO 13137)
ISO 9276-2, Representation of results of particle size analysis — Part 2: Calculation of average particle
sizes/diameters and moments from particle size distributions
ISO 9276-4, Representation of results of particle size analysis — Part 4: Characterization of a classification
process
ISO 9276-6, Representation of results of particle size analysis — Part 6: Descriptive and quantitative
representation of particle shape and morphology
ISO 13322-1, Particle size analysis — Image analysis methods — Part 1: Static image analysis methods
ISO/TS 21361, Nanotechnologies — Method to quantify air concentrations of carbon black and amorphous silica
in the nanoparticle size range in a mixed dust manufacturing environment
ISO/TS 21383 Microbeam analysis — Scanning electron microscopy — Qualification of the scanning electron
microscope for quantitative measurements
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 1540 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at https://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
3.1
aspect ratio
ratio of length of a particle to its width
[SOURCE: ISO 14966:2002, 3.7] [2]
3.2
blank
NOAA count made on a sample prepared from an unused filter or substrate to determine the background
measurement
Note 1 to entry: Background in this context means the clean substrate structure.
3.3
cluster
structures on which four or more particles or bundles, are randomly oriented in a connected grouping
[SOURCE: ISO 14966:2002, 3.10] [2]
3.4
collection substrate
flat substrate used for collecting particles and subsequent EM analysis
Note 1 to entry: Examples of substrates: a filter, TEM grid or silicon wafer.
3.5
contrast (of an image)
difference between the intensity of the particle image with respect to the background near to the particle
[SOURCE EN 13322-1:2024, 3.1.3]
3.6
energy-dispersive X-ray analysis
measurement of the energies and intensities of X-rays by use of a solid-state detector and multi-channel
analyser system
[SOURCE: ISO 14966:2002, 3.12] [2]
3.7
Feret diameter
distance between two parallel lines which are tangent to the perimeter of a particle
Note 1 to entry: The Feret diameter is a measure of an object size along a specified direction; it is applied to projections
of a three-dimensional object on a two-dimensional plane.
3.8
fibre bundle
structure composed of apparently attached, parallel fibres
[SOURCE: ISO 14966:2002, 3.14] [2]
Note 1 to entry: A fibre bundle may exhibit diverging fibres at one or both ends. The length is defined as equal to the
maximum length of the structure, and the diameter is defined as equal to the maximum width of the compact region.
Note 2 to entry: “Parallel” shall not be a requirement, since very flexible CNTs can entangle without actually aligning.
3.9
high aspect ratio object
object (hybrid aggregate, fibre aggregate, fibre cluster) with an aspect ratio > 3
3.10
image analysis
processing and data reduction operation which yields a numerical or logical result from an image
[SOURCE: ISO 13322-1:2014, 3.1.8]
3.11
image field
surface area of the sample substrate (e.g. filter, grid) which is shown on the EM display
[SOURCE: ISO 14966:2002, 3.18] [2]
3.12
limit of detection
calculated airborne particle concentration, equivalent to the upper 95 % confidence limit of 2,99 structures
predicted by the Poisson distribution for a count of zero particles
[SOURCE: ISO 14966:2002, 3.19] [2]
3.13
low aspect ratio object
object (hybrid aggregate, fibre aggregate, fibre cluster) with a length < 5 µm and an aspect ratio > 3
3.14
maximum Feret diameter
maximum length of an object whatever its orientation
[SOURCE: ISO/TR 945-2:2011, 2.1] [3]
3.15
measurement frame
selected area from the field of view in which particles are sized and counted for image analysis
[SOURCE: ISO 13322-1:2014, 3.1.10]
3.16
minimum Feret diameter
minimum length of an object whatever its orientation
[SOURCE: EN ISO 21363:2022, 3.4.5]
3.17
particle diameter
geometric diameter of a particle
Note 1 to entry: Particle diameter is often referred to simply as ‘particle size’.
3.18
pixel
smallest element of an image that can be uniquely processed, and is defined by its spatial coordinates and
encoded with colour values
[SOURCE: ISO 12640-2:2004, 3.6] [4]
Note 1 to entry: EM images always come in greyscale.
3.19
primary particle
original source particle of agglomerates or aggregates or mixtures of the two
[SOURCE: ISO 26824:2022, 1.4] [5]
3.20
projected area equivalent diameter
diameter of a circle having the same area as the projected image of the particle
[SOURCE: ISO 13322-1:2014, 3.1.1]
3.21
threshold
grey level value which is set to discriminate objects of interest from background
[SOURCE: ISO 13322-1:2014, 3.1.14]
3.22
WHO object
originally describing elongated particles with minimum length of 5 µm, a diameter between 0,2 µm and 3 µm
and a minimum aspect ratio of 3:1
Note 1 to entry: In this document, the lower diameter limit is determined by the pixel size of the EM images.
4 Abbreviations
APS Aerodynamic Particle Sizer
CP Coarse Particle
EDX Energy-Dispersive X-ray Analysis
EM Electron Microscopy
EPC Environmental Particle Counter
ESZ Electrical Sensing Zone
FEG Field Emission Gun
HAR High Aspect Ratio
HARFB High Aspect Ratio Fibre Bundle
HARFC High Aspect Ratio Fibre Cluster
HARFO High Aspect Ratio Fibre Object
LAR Low Aspect Ratio
LARFB Low Aspect Ratio Fibre Bundle
LARFC Low Aspect Ratio Fibre Cluster
LARPA Low Aspect Ratio Particle Agglomerate/Aggregate
LARPO Low Aspect Ratio Particle Object
MPPS Most Penetrating Particle Size
NOAA Nano-Objects and their Aggregates and
Agglomerates > 100 nm
OELV Occupational exposure limit value
PSD Particle Size Distribution
SEM Scanning Electron Microscope
SMPS Scanning Mobility Particle Sizer
STEM Scanning Transmission Electron Microscope
TEM Transmission Electron Microscopy
WHO World Health Organization
NOTE EDX is sometimes called EDS
5 Procedure
5.1 General
Airborne nano-objects, aggregates and agglomerates (NOAA) consists of objects in the nano to micron size
range. EM techniques shall be used to identify the nature and chemical identity of the full size range of
airborne NOAA and thus contributing to a complete workplace exposure assessment.
To be able to use EM techniques, first airborne NOAA shall be sampled by collecting the objects in a certain
volume of air on a collection medium. To identify NOAA and analyse them by EM, specific methods of sample
collection, preparation and analysis shall be used. Sampler devices and sampling procedures are described in
detail in Clause 6.
NOTE Despite the different requirements of scanning electron microscopy (SEM) and transmission electron
microscopy (TEM) that affect the way samples are collected and prepared for analysis, it is necessary for both techniques
to collect uniform deposits, with minimal probability of overlapping of the objects. This is especially valid in the
framework of an exposure assessment for compliance testing against occupational exposure limits (OELV).
The objects on the collection medium shall be in the same object size range which workers are potentially
exposed to, from single nano-objects to micron sized agglomerates and aggregates.
EM analyses are used to determine object sizes, their particle size distributions (PSD) and morphology (such
as nanofibres, platelets or spherical particles). Electron microscopes are often equipped with detectors for
chemical identification, such as an energy-dispersive X-ray system (EDX), allowing the determination of the
elemental composition of the particles. Detailed analysis procedures and counting rules for airborne NOAA
are described in Clause 7.
5.2 Basic approach
For the determination and characterization of airborne NOAA in the workplace, the following stages shall be
considered:
1) Determine measurement objectives, such as NOAA characterization, indication particle number
concentration and/or compliance testing (< > OELV, according to EN 689 and EN 482);
2) Determine workplace characteristics, such as activities, nanomaterials, exposure estimates;
3) Determine sampling strategy: selection of sampling device and collection media, specification of
measurement procedure; i.e. amount of samplers, duration of sampling, position of samplers.
NOTE Additional guidelines and strategies of workplace exposure measurements are described in EN 17058 and
ISO/TR 27628.
4) Determine the analysis strategy: selection of the microscope and settings (according to ISO/TS 21383,
ISO/TS 21361), determination of the analysis procedure (see EN ISO 19749, EN ISO 21363), i.e. off-line
vs online, manual vs automatic, with/without EDX, measurands and desired results.
5) Perform measurements, including sampling, sample preparation, EM image acquisition and object
characterization and counting;
6) Process the obtained EM data: calculate the 95 % confidence interval of the number concentration and/or
particle size distribution (according to ISO 9276-2, −4, −6 and ISO 13322-1), data evaluation and quality
control, data presentation and reporting (Clauses 8 and 9).
5.3 EM within the exposure assessment framework
In general, the objectives of an exposure assessment can vary widely and can include exposure exploration
and determination, evaluation of the effectiveness of exposure control measures, check for compliance with
occupational exposure limits (OELV) or other benchmark level, and can contribute to risk assessment and
epidemiological studies. The measurement strategy depends amongst other factors (e.g. workplace situation,
type of NOAA, emission sources/concentrations), on the objective of the assessment. EN 17058 and
ISO/TR 27628:2007 [6] give general guidance on workplace exposure assessment by inhalation of NOAA and
describes measuring devices and measurement methods for the characterization of NOAA exposure. In
addition, ISO/TR 27628 provides background information on the mechanisms of nanoparticle aerosol
formation and transportation within an occupational setting and on industrial processes associated with
nanoparticle aerosol exposure.
Several measuring methods of characterizing exposures are covered and specific information is provided on
single particle analysis with EM techniques. Each individual measurement method has its drawbacks, but
when used in combination, they give an initial insight into the presence of NOAA in the workplace. More
specific, a combination of direct-reading instruments and NOAA sampling techniques with subsequent off-
line analysis is in most workplace situations the best approach to gain insight into the occupational exposure
of NOAA. EM techniques can be used to get in depth information on size and morphology of objects and are
indispensable for the determination of number concentrations in mixed dust situations and for non-spherical
nanoparticles (nanofibres and nanoplatelets).
EN 17058 gives guidance on different levels of exposure assessment in a tiered-approach framework.
5.4 Apparatus and materials
5.4.1 General
To perform an exposure assessment to airborne NOAA, various apparatuses and materials are necessary.
5.4.2 Air sampling
— Sampler: for air sampling a suitable sampler shall be used depending on the measurement objective.
Various samplers are available commercially. An overview is shown in A.1. Annexes B to D provide
examples of sampling efficiencies and collection efficiencies of selected samplers.
— Collection medium: the sampler is equipped with a collection medium (A.2). Collection media used for
collecting airborne NOAA and their subsequent EM analysis have to fulfil some prerequisites. They shall
be flat with a uniform surface and preferably electrically conductive to avoid local charging during EM
imaging. In addition, during imaging with EM they have to provide a uniform background signal. For SEM
different filter membranes, solid wafer pieces, metallic substrates as well as TEM-grids are possible
collection substrates. For TEM only TEM grids are possible substrates.
— Pump: the pump shall be chosen according to the necessary volumetric airflow of the sampler and the
characteristics of the collection substrate used (e.g. pressure drop created by the pore size of the filter),
(see A.3).
5.4.3 Sample pre-treatment
5.4.3.1 Plasma cleaner and/or coater: The choice of collection medium will be dictated by the type of
sampler and the analytical considerations (e.g. SEM or (S)TEM). For filter samples in special cases (e.g.
charging effects, contamination) plasma cleaning and/or coating shall be applied (A.4).
NOTE 1 For samples collected on TEM grids, no coating is necessary and plasma cleaning is not recommended.
NOTE 2 Make sure to perform the plasma cleaning prior to (sputter) coating.
5.4.4 Analysis
— Electron microscope: object analysis can be conducted in a scanning electron microscope (SEM) or
(scanning) transmission electron microscope ((S)TEM). Both types of instruments can be fitted with
various detectors to record multiple signals, electrons and radiation, emitted from the interaction of the
electron beam with the sample. Those detectors can determine the (elemental) composition and
chemically identify particles. More information on EM selection and qualification and instrument settings
and conditions are given in A.5. More specific information on the use of electron microscopes for particle
analysis can be found in EN ISO 21363 and EN ISO 19749. Detailed technical information on the
qualification of SEMs for quantitative analysis can be found in ISO/TS 21383.
The resolution of the microscope shall be at least four times higher than the minimum diameter of the
smallest nano-objects present. For imaging NOAA, with diameters of individual nano-objects below
10 nm, a TEM or high resolution SEM with field emission source is required.
For objects sizes below 5 nm (i.e. nanorods) a TEM is highly recommended.
— Image analysis software: the purpose of image analysis is to measure size and morphological features,
such as shape, of the present objects on the sample surface. Conventional image analysis is based on
algorithms, set to recognize and detect particles upon their grayscale level (thresholding) and can be
performed in-operando and offline. More information is given in A.6.
NOTE Be aware that not all image analysis software has been validated.
6 Sampling
6.1 Sampling strategy
Electron microscopic techniques are powerful in-depth techniques, however, the analysis of EM samples is
very sensitive to the level of sample load, and thus require careful consideration of the sampling strategy.
Sampling of NOAA starts with setting up a sampling strategy, which is based on the objectives of the
measurements. When determining the objectives, it is important to take into account special aspects of the
workplace situation.
The optimum position for collection of air samples shall be determined after a complete survey of the location
(initial assessment phase). Detailed information on the process conditions, object types (nanofibres,
nanoplatelets or nanoparticles) and, if known, size ranges of the airborne NOAA shall be acquired prior to
sampling. In addition, if the workplace is (partly) outdoors, the outdoor environment shall be taken into
account as well, such as weather conditions. All available information such as local topography shall be
recorded. Furthermore, the position of the samplers shall be carefully recorded. Also, timing of sampling shall
be taken into account.
It is essential to define the objective of the measurements, before samples are collected, such as the level of
exposure assessment and the desired information/results. Available information on emission sources and
local situations shall be taken into account, as stated in the initial assessment of EN 17058. The best sampler
and sample substrate shall be selected based on the objectives of the measurements.
A sufficient number of samples shall be collected and depending on the objectives and the level of the
workplace, assessment by sequential multipoint sampling might be necessary to provide adequate
characterization. The collection medium needs to be appropriately loaded for EM analysis, resulting in a
uniform and homogeneous deposit, with a minimum of overlapping of the objects. Therefore, substrate
material, pore sizes, sampling flows and sampling time play an important role.
Furthermore, the particles on the collection medium shall be in the same particle size range which workers
are potentially exposed to, from single nano-objects to micron sized agglomerates and aggregates.
If the measurement objectives and workplace characteristics are determined and the sampling and analysis
strategies are in place, the sampling procedure shall be started.
6.2 Collection of air samples
6.2.1 General
For sampling collection of airborne NOAA, suitable samplers shall be used that contribute to the scope of
measurements. Before use, samplers shall be pre-cleaned and checked for defects. The samplers shall be
operated according to the manufacturer’s instructions.
The sampling (vacuum) pump shall be connected to the EM sampler with a flexible tubing and the flow rate
of the sampler needs to be adjusted. Sampling pumps shall meet the requirements of EN ISO 13137 and shall
be operated according to the manufacturer’s instructions. Test conditions, test methods and instructions for
use shall be followed according to EN ISO 13137.
NOTE At the end of sampling, cover the sampler, to avoid contamination and preferably hold the samplers upright
(sampled collection medium surfaces face-upwards). Transport the sampler to the EM laboratory for analyses.
If deposits are observed around the edge of the substrate or on unexposed edges of the sampling holder, a
leak around the substrate has occurred and the sample shall be rejected.
6.2.2 Personal and area sampling
For a basic exposure assessment area (fixed-point) sampling can be performed, but several considerations
shall be made when choosing a proper location, e.g. distance to the source, ventilation/airflows, movement of
the workers. The sampler shall be oriented according to the manufacturer’s requirements. For area sampling,
there are basically no restrictions for EM sampling techniques and pumping devices.
For a comprehensive assessment of the exposure by inhalation, measurements in the breathing zone are
necessary. To allow free movement of the workers, small wearable and battery-based sampling pumps need
to be worn by the worker with the inlet of the EM sampler placed within a hemisphere of 30 cm within the
breathing zone of the person. There are certain restrictions for personal air sampling. The EM sampler shall
be physically placed in the breathing zone and the worker shall not be inconvenienced by it, in a way that his
movements are hindered. Additionally, the capacity of the personal air pump needs to be considered when
choosing the sampler and collection substrate. If personal breathing zone measurements are not possible, a
comprehensive assessment of the exposure by inhalation cannot be performed.
6.2.3 Time, duration and frequency of sampling
Depending on the sampling techniques, the sampling time can vary. For compliance testing, the sampling time
(sampling period) shall be representative of the reference period of the OELV.
NOTE For example, a full shift average concentration, typically the 8 h time-weighted concentration, gives a
representative description of the occupational exposure situation. If possible, the sampling period is equal or close to 8 h
with a minimum of 4 h.
For objects (size) counts, the sample substrate needs to be appropriately loaded to allow efficient analysis,
while avoiding object agglomeration and overloading. In A.4 of ISO/TR 27628:2007 [6], details can be found
of the calculation of sample collection times.
6.3 Collection and sampling efficiencies
Sampling and collection efficiencies play an important role in the sampler selection. As well as the ability of
the sampler to collect uniform and homogeneous deposits, with a minimum of overlapping objects. In this
document samplers were validated during three Round Robins. Table B.1 to B.7 in Annex B present a
summary of the collection efficiencies of 8 tested samplers for different types of NOAA, Annex C shows results
of collection efficiencies specific for fibrous objects. Annex D gives examples of complete overall sampling
efficiency curves of 4 selected filter-based samplers for NOAA from around 30 nm to around 30 µm and
provides information on the sampling of both submicronic nano-objects and micronic aggregates and
agglomerates. The results presented in Annexes B to D shall be used as guideline to select the best possible
sampler.
6.4 Transport, handling and storage
Overall, the samplers, and collected samples, shall be handled carefully. During transport and storage, the
samples shall be stored in labelled anti-static containers and shall be stored upright in dust-tight sample
containers. The sampler holder needs to be covered at all times during transport and storage to prevent
contamination of the collection medium. The cover shall be anti-static and only be removed in the laboratory
for sample preparation and for insertion into the EM instrument. In the laboratory, the transported containers
shall be visually checked for signs of disturbance.
7 Analysis
7.1 Analysis strategy
7.1.1 General
There are multiple procedures to analyse a collection medium surface using EM techniques. Procedures shall
be performed manually or (semi-) automatically, online or via micrographs (offline) (see A.6).
7.1.2 Differentiation of particles
If a variety of objects are present (mixed dust) at the collection medium surface, object differentiation shall
be performed based on morphology and/or shape if particles have clearly differing morphologies (e.g. fibres
vs. spherical particles), or their z-contrast visible when using BSE electrons for imaging. If the objects cannot
be distinguished via the above, chemical identification (e.g. by EDX detector, see A.5.2) is necessary for an
unambiguous identification of particles with the same morphology and contrast.
7.1.3 Image resolution and magnifications
Micrographs shall be taken with a physical resolution high enough to visualise all relevant particles and allow
geometric characterization. Ideally, one fixed magnification is used to analyse both primary nano-objects as
well as agglomerates and aggregates. If at the chosen image size (to be able to observe the larger agglomerates
and aggregates) the resolution (pixel size) is not sufficient to analyse the primary nano-objects, multiple fixed
magnifications can be used to obtain a complete particle size distribution (see Clause 8). In this case, multiple
subsets of images are acquired, respective for the selected pixel sizes. Each subset requires its own particle
analysis and counting. A mixture of images with different pixel sizes for this purpose is not valid.
7.2 Preparation of samples
Samples arriving at the laboratory shall be examined visually. Before sample preparation and analysis, the
collection medium needs to be examined on uniformity of deposition. If the deposition shows evidence of non-
uniformity, the sample shall be rejected.
For EM analyses, the medium shall be mounted onto a stub (a common mounting method is to use double-
sided adhesive conducting carbon pads, augmented with spot-application of colloidal silver or carbon to
ensure a clear conducting pathway between the top of the sample and the specimen support), or media could
be placed completely in sample holders, or could be placed directly into the EM chamber (e.g. TEM grids).
Mounting depends on sample and instrument type and is the responsibility of the operator.
For SEM there needs to be a conductive pathway between the point at which the electron beam hits the
substrate surfaces. Localized charging of the substrate during SEM measurements and poor imaging needs to
be minimized. Additional preparation techniques such as vacuum evaporator, plasma asher and (sputter)
coater could be used to improve the image.
7.3 Sample Quality check
The first sample quality check using EM, after collection of airborne NOAA, consists of observing the sample
substrate at low to high resolution (magnification e.g. 100 – 100 000x). An image series with stepwise increase
of magnification is acquired containing the information necessary to assess the sample quality based on the
following criteria:
— No impairment of sample physical integrity: low resolution (overview image). The physical integrity
of the sample collection medium is unaffected after sampling. No visible damage apart from peripheral
marks by e.g. tweezers originating from sample transfer from the sampler to the EM table is observed.
— No contamination: low resolution. The sample shall be free from coarse objects (size > 100 µm) that do
not stem from the aerosol sampling. Presence of large particles indicate sample contamination.
— Continuous particle load: medium resolution (appropriate pixel size to visualize objects). The objects
shall be distributed homogeneously on the collection medium surface. As a first analysis, the sample shall
be screened for sections devoid of or overly loaded with objects compared to the majority of the sample.
For a statistical analysis as a prerequisite for extrapolating particle number concentration from particle
number density on the sample.
— Fibres lay flat: working resolution (appropriate pixel size for object characterization). High aspect ratio
(HAR)-objects shall be deposited on the collection medium in a planar manner ideally without them
pointing in a vertical direction.
In case the sample does not match quality criteria, the sample shall not be used to determine airborne NOAA
concentrations with the objective for compliance testing. However, the sample could still be used for
indicative measurements e.g. for particle size distribution, even if samples are locally disturbed. In both cases
the quality criteria needs to be reported and judged.
For many collection media, surface features can resemble objects. In particular for track-edge membrane,
irregularities in the gold coating might lead to local charge spikes that result in brighter artefacts in the
otherwise dark background. Prior to the sampling campaign, one unused representative of the used badge or
LOT of sample substrates shall be checked for the regular occ
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