ASTM E2535-07(2018)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E2535 − 07 (Reapproved 2018)
Standard Guide for
Handling Unbound Engineered Nanoscale Particles in
Occupational Settings
This standard is issued under the fixed designation E2535; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Nanometre-scale particles are encountered in nature and in industry in a variety of forms and
materials. Engineered nanoscale particles as a class comprise a range of materials differing in shape,
size, and chemical composition, and represent a broad range of physical and chemical properties.
Workers within some nanotechnology-related industries and operations have the potential to be
exposed to these engineered nanoscale particles at levels exceeding ambient nanoscale particle
concentrations through inhalation, dermal contact and ingestion when not contained on or within a
matrix (unbound). Occupational health risks associated with manufacturing, processing and handling
unbound nanoscale particles, agglomerates, or aggregates of nanoscale particles are not yet clearly
understood.Dominantexposureroutes,potentialexposurelevelsandanymaterialhazardareexpected
to vary widely among particular nanoscale particle materials and handling contexts. Additional
research is needed to understand the impact of these exposures on employee health and how best to
devise appropriate exposure monitoring and control strategies. Until clearer understandings emerge,
the limited evidence available suggests caution when potential exposures to unbound engineered
nanoscale particles (UNP) may occur.
1. Scope empirical knowledge of and experience with handling UNP
materials, the purpose of this guide is to offer general guidance
1.1 This guide describes actions that could be taken by the
on exposure minimization approaches for UNP based upon a
user to minimize human exposures to unbound, engineered
consensus of viewpoints, but not to establish a standard
nanoscale particles (UNP) in research, manufacturing, labora-
practice nor to recommend a definite course of action to follow
tory and other occupational settings where UNP may reason-
in all cases.
ably be expected to be present. It is intended to provide
1.2.1 Accordingly, not all aspects of this guide may be
guidance for controlling such exposures as a cautionary mea-
relevant or applicable to all circumstances of UNP handling.
sure where neither relevant exposure standards nor definitive
The user should apply reasonable judgment in applying this
hazard and exposure information exist.
guide including consideration of the characteristics of the
1.2 General Guidance—This guide is applicable to occupa-
particular UNP involved, the user’s engineering and other
tional settings where UNP may reasonably be expected to be
experience with the material, and the particular occupational
present. Operations across those settings will vary widely in
settings where the user may apply this guide. Users are
the particular aspects relevant to nanoscale particle exposure
encouraged to obtain the services of qualified professionals in
control. UNPrepresent a vast variety of physical and chemical
applying this guide.
characteristics (for example, morphology, mass, dimension,
1.2.2 Applicable Where Relevant Exposure Standards Do
chemical composition, settling velocities, surface area, surface
Not Exist—This guide assumes that the user is aware of and in
chemistry) and circumstances of use. Given the range of
compliance with any authoritative occupational exposure stan-
physical and chemical characteristics presented by the various
dardapplicabletothebulkformoftheUNP.Thisguidemaybe
UNP, the diversity of occupational settings and the uneven
appropriate where such exposure standards do not exist, or
where such standards exist, but were not developed with
This guide is under the jurisdiction of ASTM Committee E56 on Nanotech-
consideration of the nanoscale form of the material.
nology and is the direct responsibility of Subcommittee E56.03 on Environment,
Health, and Safety.
1.3 Applicable Where Robust Risk Information Does Not
Current edition approved Oct. 1, 2018. Published October 2018. Originally
Exist—This guide assumes the absence of scientifically sound
approved in 2007. Last previous edition approved in 2013 as E2535 – 07 (2013).
DOI: 10.1520/E2535-07R18. risk assessment information relevant to the particular UNP
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2535 − 07 (2018)
involved. Where sound risk assessment information exists, or 1.7 Not a Standard of Care—This guide does not necessar-
comes to exist, any exposure control measures should be ily represent the standard of care by which the adequacy of a
designed based on that information, and not premised on this set of exposure control measures should be judged; nor should
guide. Such measures may be more or less stringent than those this document be used without consideration of the particular
suggested by this guide. materials and occupational circumstances to which it may be
applied. The word “standard” in the title means only that the
1.4 Materials Within Scope—This guide pertains to un-
document has been approved through the ASTM consensus
bound engineered nanoscale particles or their respirable ag-
process.
glomerates or aggregates thereof. Relevant nanoscale particle
types include, for example, intentionally produced fullerenes, 1.8 The values stated in SI units are to be regarded as
nanotubes, nanowires, nanoropes, nanoribbons, quantum dots, standard. No other units of measurement are included in this
nanoscale metal oxides, and other engineered nanoscale par- standard.
ticles. Respirable particles are those having an aerodynamic
1.9 This standard does not purport to address all of the
equivalent diameter (AED) less than or equal to 10 µm (10 000
safety concerns, if any, associated with its use. It is the
nm) or those particles small enough to be collected with a
responsibility of the user of this standard to establish appro-
respirable sampler (1-3). The AED describes the behavior of
priate safety, health, and environmental practices and deter-
an airborne particle and is dependent upon the particle density,
mine the applicability of regulatory limitations prior to use.
shape,andsize—forinstance,aparticlewithasphericalshape,
1.10 This international standard was developed in accor-
smooth surface, density of 1.0 g/cc and a physical diameter of
dance with internationally recognized principles on standard-
4 µm would have an AED of 4 µm, whereas a particle with a
ization established in the Decision on Principles for the
spherical shape, smooth surface, density of 11.35 g/cc and a
Development of International Standards, Guides and Recom-
physical diameter of 4 µm would have an AED of 14 µm and
mendations issued by the World Trade Organization Technical
would therefore be of a nonrespirable size. Respirable fibers
Barriers to Trade (TBT) Committee.
are those having physical diameters less than or equal to 3 µm
(3000 nm) or those fibers small enough to be collected with a
2. Referenced Documents
thoracic sampler (4, 5).
2.1 ASTM Standards:
1.5 Materials Beyond Scope:
E2456 Terminology Relating to Nanotechnology
1.5.1 UNP may be present in various forms, such as
F1461 Practice for Chemical Protective Clothing Program
powders or suspensions, or as agglomerates and aggregates of
primary particles, or as particles dispersed in a matrix. This 3. Terminology
guide does not pertain to UNPincapable, as a practical matter,
3.1 Definitions—Refer to Terminology E2456 for defini-
from becoming airborne or be expected to generate or release
tions of terms used within this guide.
UNP in occupational settings under the particular circum-
3.2 Definitions of Terms Specific to This Standard:
stancesofuse(forexample,UNPsdispersedorotherwisefixed
3.2.1 aerodynamic equivalent diameter (AED), n—the di-
within a solid, strongly bonded to a substrate or contained
ameter of a smooth, unit density [ρ = 1 gram per cubic
within a liquid matrix such as aggregated primary crystals of o
centimetre (g/cm )] sphere that has the same terminal settling
pigments in paints). This guide does not pertain to aggregates
velocity as the actual particle (6).
or agglomerates of UNP that are not of a respirable size.
1.5.2 This guide does not pertain to materials that present 3.2.2 agglomerate, n—in nanotechnology, a group of par-
nanoscale surface features, but do not contain UNPs (for
ticlesheldtogetherbyrelativelyweakforces(forexample,van
example,nanoscalelithographyproducts,nanoelectronicstruc- derWaalsorcapillary.)andwhichmaybreakapartintosmaller
tures or materials comprised of nanoscale layers).
particles upon processing.
1.5.3 This guide does not pertain to UNPs which exist in
3.2.3 aggregate, n—in nanotechnology, a discrete group of
naturewhichmaybepresentinnormalambientatmospheresor
particles in which the various individual components are not
are unintentionally produced by human activities, such as by
easilybrokenapart,suchasinthecaseofprimaryparticlesthat
combustion processes. Nor does it pertain to materials that
are strongly bonded together (for example, fused, sintered, or
have established exposure control programs (for example, safe
metallically bonded particles).
handling protocols for nanoscale biological agents) or pub-
3.2.4 control principle, n—the principle establishes in this
lished exposure limits such as occupational exposure limits for
guide that, as a cautionary measure, occupational exposures to
welding fumes. See Appendix X1.
unbound, engineered nanoscale particles (UNP) should be
1.6 Handling Considerations Beyond Scope—The use of
minimizedtolevelsthatareaslowasisreasonablypracticable.
this guide is limited to the scope set forth in this section. This
3.2.5 nanoscale, adj—having one or more dimensions on
guide generally does not address actions related to potential
the order of 1 to 100 nanometres.
environmental exposures, nor to exposures potentially arising
at disposal or other end-uses.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The boldface numbers in parentheses refer to the list of references at the end of Standards volume information, refer to the standard’s Document Summary page on
this standard. the ASTM website.
E2535 − 07 (2018)
3.2.6 particle, n—in nanotechnology, a small object that 5. Significance and Use
behaves as a whole unit in terms of transport and properties.
5.1 This guide is intended for use by entities involved in the
3.2.7 program, n—a management policy to minimize occu-
handling of UNP in occupational settings. This guide covers
pational UNP exposures together with the procedures and
handling principles and techniques that may be applied, as
actions to meet that objective.
appropriate, to the variety of UNP materials and handling
settings. These settings include research and development
3.2.8 respirable, adj—airborne particles which are small
activities, material manufacturing, and material use and pro-
enough to enter the alveolar (gas-exchange) region of the lung.
cessing. This guide may also be used by entities that receive
3.2.9 inhalable, adj—airborne particles which are small
materials or articles containing or comprising nanoscale par-
enoughtoentertheheadairwaysthroughthenoseormouth,or
ticles fixed upon or within a matrix (that is, bound nanoscale
both, during inhalation.
particles), but whose own processes or use may reasonably be
3.2.10 should, aux., v—as used in this guide, indicates that
expected to cause such particles to become unbound.
a provision is not mandatory but is recommended as a good
practice.
6. Establishing a Program to Implement the Control
3.2.11 ultrafine particle, n—aparticlesmallerthanabout0.1 Principle
micrometre (100 nanometres) in diameter.
6.1 Process for Establishing Program—To attain the inte-
3.2.12 unbound, adj—with reference to engineered na-
grated effort needed to minimize UNP exposures consistent
noscale particles, those nanoscale particles that are not con-
with the control principle, the user should develop a program
tained within a matrix under normal temperature and pressure
that addresses the efforts in all management, planning and
conditions that would reasonably be expected to prevent the
operational phases of the enterprise to be taken to achieve that
particlesfrombeingseparatelymobileandapotentialsourceof
objective.The principal topics of this guide outline an iterative
exposure. An engineered primary nanoscale particle dispersed
processtypicalofmanyoccupationalsafetyregimestheuserof
and fixed within a polymer matrix, incapable as a practical
this guide may adopt for the initial establishment and imple-
matter of becoming airborne, would be “bound,” while such a
mentation of an effective program to minimize occupational
particle suspended as an aerosol would be “unbound.”
UNP exposures.
3.3 Acronyms:
6.2 Management Commitment—A formal, written manage-
3.3.1 HEPA—high efficiency particulate air
ment policy should be established committing to minimizing
potential occupational UNPexposures to levels that are as low
3.3.2 MSDS—material safety data sheet(s)
as is reasonably practicable. The policy and commitment
3.3.3 PPE—personal protective equipment
should be regularly communicated throughout the organization
3.3.4 UNP—unbound engineered nanoscale particles
and reflected in (a) written administrative procedures, instruc-
tions and training materials for operations and contingencies
4. Summary of Guide
potentially involving occupational UNP exposures, (b) facili-
ties design, and (c) instructions to designers, vendors and user
4.1 This guide presents the elements of an UNP handling
personnel specifying or reviewing facility design, systems,
and exposure minimization program including considerations
operations or equipment.
and guidance, based on a consensus of viewpoints, for estab-
lishing such a program. The six principal elements are: (a)
6.3 Organization of Personnel and Responsibilities—
establishing management commitment to the control principle;
Responsibility and authority for implementing a minimization
(b) identifying and communicating potential hazards; (c) as-
program consistent with this guide should be assigned to an
sessing potential UNP exposures within the worksite; (d)
individual with organizational freedom to ensure appropriate
identifying and implementing engineering, and administrative
development and implementation of the program. This pro-
controls consistent with the control principle for all relevant
gram manager would be responsible for coordinating efforts
operations and activities; (e) documentation; and (f) periodi-
among the several functional groups (for example, operations,
cally reviewing its adequacy.
housekeeping, maintenance, engineering, safety, human
resources, sales, and shipping) that may be involved or
4.2 The Control Principle—Exposure control guidance in
impacted by the program, and should have the authority, or
this guide is premised on the principle (established in this
direct recourse to an authority, to timely resolve questions
guide)that,asacautionarymeasure,occupationalexposuresto
related to the conduct of the program. The program manager
UNP should be minimized to levels that are as low as is
should be knowledgeable, or adequately supported by persons
reasonably practicable. This principle does not refer to a
who are knowledgeable, concerning the characteristics of the
specific numerical guideline, but to a management objective,
UNP involved, all aspects of the organization’s processes and
adopted on a cautionary basis, to guide the user when (a)
worker activities involving UNP, relevant engineering expo-
assessing the site-specific potential for such exposures; (b)
sure control methods, and the organization’s best information
establishing and implementing procedures to minimize such
concerningthepotentialoccupationalsafetyandhealthrisksof
exposures; (c) designing facilities and manufacturing pro-
relevant UNP exposure.
cesses; and (d) providing resources to achieve the objective.
Additionaldiscussionoftheapplicationofthecontrolprinciple 6.3.1 Responsibilities of the program manager should in-
is set forth in Annex A1. clude to (a) establish and maintain a program that implements
E2535 − 07 (2018)
the management commitment to the control principle, includ- being applied; (c) provide the basis for efficient and informed
ingspecificgoalsandobjectives; (b)ensurethedevelopmentof future periodic evaluations of the potential need to amend the
appropriate procedures and practices by which the specific program by documenting the practicable engineering and
goals and objectives will be met; (c) ensure the resources administrative controls adopted and the rationale for their
needed to achieve the goals and objectives are made available selection among other options; and (d) serve as a training and
as deemed appropriate; (d) regularly communicate progress operationalreferenceforthevarioususerpersonnelresponsible
and status information to the user’s management. for implementing aspects of the program.
6.3.2 Responsibilities of all supervisory personnel should
6.5.2 The extent and form(s) of the documentation should
include to (a) communicate the management commitment to
be tailored to the user’s individual circumstances consistent
the control principle to user personnel at all levels; (b) ensure
with (a) meeting the foregoing documentation objectives; (b)
that the persons within their respective areas of supervisory
practical utility; (c) updating the documentation over time; and
responsibility have received requisite training in the program;
(d) the scale and extent of the user’s relevant operations.
(c) ensure support from personnel for attaining exposure
Depending on the user’s individual circumstance, documenta-
minimization objectives, including compliance with applicable
tion to be prepared, maintained and updated (as applicable)
work rules related to the program; (d) ensure personnel and
may include:
facilities are properly equipped consistent with program re-
6.5.2.1 Allocation of organizational responsibilities for the
quirements; (e) participate in design and process reviews and
program;
development of procedures in connection with the program to
6.5.2.2 Material characterization and safety information (in-
the extent affecting or involving their areas of supervisory
cluding underlying basis documentation where the user devel-
responsibility; and (f) support the program manager in formu-
oped the data or analysis);
lating and implementing the program.
6.5.2.3 Documentation of qualitative or quantitative, or
6.4 Training and Supervision—The program should include
both, exposure assessments, risk assessments, and hazard
instructing all personnel (including contractor personnel)
analysis;
whose duties may involve potential exposure to UNP, or who
6.5.2.4 Relevant engineering and other analyses supporting
direct the activities of others whose duties may involve
selection of equipment and operating parameters, including the
potential exposure to UNP. Personnel who do not ordinarily
manufacturer’s performance and other specifications for such
enter work areas containing UNP may also require limited
equipment and alternatives considered;
instruction in the user’s workplace exposure minimization
6.5.2.5 Work rules, work practices, standard operating
program (for example, to respect any access restrictions or
procedures, policies, and response plans adopted to implement
personalprotectiveequipmentrequirements).Personnelshould
the control principle;
receive initial training and periodic refresher training.
6.5.2.6 Employeetrainingmaterialsandinitialandrefresher
6.4.1 Training should emphasize the importance of UNP
training schedules;
exposure minimization as a management objective. The train-
6.5.2.7 Schedules and procedures for periodic substantive
ing should be commensurate with duties and responsibilities of
review and modification of the program as appropriate, updat-
those receiving the instruction, as well as the magnitude of the
ing program documentation, and reporting results; and
potential exposure that might reasonably be expected.Training
6.5.2.8 Equipment maintenance, certification and calibra-
should include instruction on relevant hazard information,
tion schedules.
instruction on the exposure minimization work rules, work
practices, operating procedures and emergency response pro-
6.6 Periodic Review of Program—At least annually the
cedures developed and implemented at the facility. Copies of
programshouldbereviewedtoensurethatthe programdesign,
these rules and procedures should be available to those
scope and implementation continue to be effective in meeting
receiving instruction.
the management objective of the control principle. Amend-
6.4.2 Personnel (including contractor personnel) who direct
ments to the program should be based on the results of any
the activities of others should have the authority and respon-
more current empirical research in relevant disciplines (for
sibility to implement the program. During operations in UNP
example, toxicology, epidemiology, exposure measurement,
work areas, adequate supervision should be provided to ensure
and exposure control and prevention), the development or
that appropriate procedures are followed, that planned precau-
amendment of relevant and authoritative occupational expo-
tions are observed, and that all potential exposure circum-
sure limits and test methods, changes in workplace processes
stances that develop or are recognized during operations or
or personnel, the results of workplace monitoring, lessons
incidents are addressed in a timely and appropriate manner.
learned from any unplanned exposure or potential exposure
incidents (for example, accidental spills, releases), the results
6.5 Documentation of Program—The user’s program
of any medical surveillance, any worker observations or
should be recorded in a written form and should contain
complaints relevant to the program and the results of any new
sections that address each of the principal topics presented in
job hazard or process safety analyses.
this guide.
6.5.1 The objectives for preparing and maintaining such 6.6.1 Additional program reviews of relevant scope should
documentation should be to (a) record the management com- beconductedinconnectionwithanyproposedprocesschanges
mitmenttothe control principle; (b)provideanongoingmeans potentially impacting UNP exposure control, and indicated by
todemonstratetousermanagementthatthe control principleis the results of incident or accident follow-up investigation such
E2535 − 07 (2018)
as failure analysis in relation to any unplanned UNP exposure 7.1.2.11 Crystal structure/crystallinity.
or potential exposure incidents.
7.2 Occupational Exposure Limits—Currently, there are no
6.6.2 Theresultsof programreviewsshouldbedocumented
published regulatory occupational exposure limits (OEL) for
and any amendments to the program determined to be war-
airborne exposures specific to UNP as a general class of
ranted should be implemented in a reasonable time frame in
particulates.Occupationalexposurelimitsdoexistfornuisance
view of the circumstances. Any changes to one aspect of the
particles (insoluble or poorly soluble) not otherwise classified
program should be carried through to other relevant compo-
and may exist for particles of similar physical and chemical
nents (for example, training, material safety data sheets or
composition to the UNP of interest. Refs (1, 13-17) identify
other documentation, and monitoring protocols).
sources of exposure limits for airborne contaminants that may
be considered in selecting target exposure limits for compara-
7. Hazard Assessment and Evaluation
tive UNP materials. It is essential that the documentation used
NOTE 1—The user should assess the UNP material anticipated to be
to derive such values be consulted, since the nanoscale form
presentintheworkplacetoidentify,totheextentpracticable,anyphysical
may have not been considered in its development, and there-
or health hazards the UNP may present in the event of acute or chronic
exposure based upon review of either (a) any material safety data sheets
fore such limits may not be relevant or adequate for poorly-
provided by the supplier or (b) the available, statistically significant,
soluble or insoluble nanoscale particles.
scientific evidence from studies conducted in accordance with established
7.2.1 Interim Occupational Exposure Limits—In the ab-
scientific principles and that are otherwise relevant and reliable indicators
of hazard. The assessment should evaluate the UNP in the condition or senceofdefinitiveoccupationalexposurelimits,itisprudentto
form in which it would be expected to be found in the workplace (for
control exposures to “as low as is reasonably practicable.” The
example, dispersed individual particles or as aggregates/agglomerates of
followingareexamplesofinterimoccupationalexposurelimits
primary particles). Where no substance-specific data are available, a
that one might consider to evaluate the effectiveness of UNP
qualitativeassessmentshouldbemadebaseduponreliabledata(asabove)
exposure controls. These are provided as examples, only, and
and authoritative standards for analogous materials (bulk or nanoscale) as
an indication of potential hazards. The method and results of the professional judgment must be exercised as to the appropriate-
assessment, even if indeterminate, should be documented.
ness of such interim limits for the specific UNP in question.
7.1 Scientific Uncertainty Concerning Most Significant
7.2.1.1 General:
Characteristics for Assessing Hazard Potential: (1) American Conference of Governmental Industrial Hy-
7.1.1 Thereislittleconsensusfortherelativesignificanceof
gienists (ACGIH) believes that all particles (insoluble or
the physical and chemical characteristics of UNP as an poorly soluble) not otherwise specified (PNOS) should be kept
3 3
indicator of toxicity. However, current research indicates that
below 3 mg/m , respirable particles, and 10 mg/m , inhalable
particle size, surface area, and surface chemistry (or activity) particles, until such time as a TLV is set for a particular
may be more important metrics than mass and bulk chemistry
substance (1). These recommendations apply only to particles
(7). that (a) Do not have an applicable TLV, (b) Are insoluble or
7.1.2 A number of sources have indicated physical and
poorly soluble in water (or, preferably, in aqueous lung fluid if
chemical characteristics that may have important health impli-
data are available); and (c) Have low toxicity (that is, are not
cations (8-12). The toxicity and health risk may be a factor of
cytotoxic, genotoxic, or otherwise chemically reactive with
the following properties, all or some of which may be
lung tissue, and do not emit ionizing radiation, cause immune
significant, or not, and whereby some properties may enhance
sensitization, or cause toxic effects other than by inflammation
the overall toxicity:
or the mechanism of “lung overload.” It is important to note
7.1.2.1 Size and size distribution;
that the ACGIH PNOS exposure limits were not based on
7.1.2.2 Shape (for example, fiber diameter, length, and
nanoscale materials and are not likely to be appropriate to
aspect ratios for individual nanotubes and bundles/ropes); apply to nanoscale particles as a general rule.
7.1.2.3 Agglomeration state;
(2) The U.S. Environmental Protection Agency (EPA) has
7.1.2.4 Biopersistence/durability/solubility; set National Ambient Air Quality Standards for particle pollu-
7.1.2.5 Surface area: “biologically available surface area,”
tion (18). Scientific studies have found an association between
“specific surface area,” “external (geometric surface area),” exposure to particulate matter and significant health problems,
and “internal (if material is porous).” Microporous or mesopo-
including:aggravatedasthma;chronicbronchitis;reducedlung
rous powders exhibit much higher surface areas than nonpo- function; irregular heartbeat; heart attack; and premature death
rous powders;
in people with heart or lung diseases. These outdoor air
7.1.2.6 Porosity; pollution standards were set to protect public health, including
7.1.2.7 Surface chemistry: “surface composition,” ”surface
the health of “sensitive” populations such as asthmatics,
energy/wettability,”“surfacecharge,”“surfacereactivity,”“ad- children, and the elderly. Though not intended for application
sorbed species,” and “surface contamination”;
inoccupationalenvironments,suchlimitsmaystillbeusefulin
7.1.2.8 Trace impurities/contaminants (for example, metal assessingexposuresinoccupationalsettings.Thelimitationsof
catalysts, polycyclic aromatic hydrocarbons, etc.);
using these values include (1) the physical-chemical composi-
7.1.2.9 “Chemical composition, including spatially aver- tion of outdoor air pollution is likely to be different than with
aged (bulk) and spatially resolved heterogeneous composi- engineered nanoscale particles, (2) those employed in the
tion”; workplace are generally considered a less sensitive population,
7.1.2.10 Physical properties (for example, density, (3) the averaging times for the EPA standards are based on
conductivity, etc.); and either 24-hour or annual averaging times, whereas averaging
E2535 − 07 (2018)
times in the workplace are usually 8 hours per day, 5 days per quartz), at least in the interim, until SWCNTs are further
week. Therefore, even if the physico-chemical composition characterized (22, 23); therefore, for at least some forms of
SWCNT, the 8-hour time-weighted occupational exposure
was similar, an argument could be made that these values
should be adjusted for application in an occupational environ- limit of 25 ug/m (that is, the ACGIH 2006 TLV-TWA for
respirable crystalline silica) may be more appropriate than a
ment. For fine particles, otherwise known as PM (particulate
2.5
matter of 2.5 µm in aerodynamic diameter and smaller), the respirable synthetic graphite OSHA PEL-TWA of 5000 ug/m
3 3
or 2006ACGIH TLV-TWAof 2000 ug/m . However, applying
EPAstandard is 35 µg/m (0.035 mg/m ) as a 24-hour average,
3 3
and15.0µg/m (0.015mg/m )asanannualarithmeticmean.A the quartz exposure limit measure for SWCNT may not
necessarily be appropriate in all instances, because the toxicity
PM air sampler collects particulate matter that can penetrate
2.5
may vary depending on various factors (for example, agglom-
into the deep part of the lung referred to as the pulmonary
eration state, functionalization, trace impurities/contaminants,
region (alveolar region where gas exchange takes place).
etc.).
Sources of fine particles in outdoor air pollution include forest
(2) Number—Donaldson et al. cites a study that demon-
fires; diesel and gasoline engines; high-temperature industrial
stratedthatMultiWalledCarbonNanoTubes(MWCNT)swere
processes, such as smelters and steel mills. For PM (particu-
highlyfibrogenicandinflammogenic,beingroughlyequivalent
late matter of 10 µm in aerodynamic diameter and smaller), the
3 3
to a chrysotile asbestos control and recommended that until
EPA standard is 150 µg/m (0.150 mg/m ) as a 24-hour
better information becomes available, that they should be
average. A PM air sampler collects particulate matter than
considered in the same way other biopersistent fibers in
couldpenetrateintoeithertheupperpartofthelungreferredto
workplace risk assessments, using similar assessment ap-
asthetracheobronchialregion(conductingairwaysofthelung)
proaches (for example, fiber counts) (9). However, this ap-
or into the deep part of the lung (pulmonary region).
proach may be questionable and difficult given that carbon
7.2.1.2 Titanium Dioxide—There are occupational exposure
nanotubes agglomerate and mechanically entangle into com-
limits for titanium dioxide, but they do not currently distin-
plex structures/clumps. The 2006 ACGIH 8-hour TLV-TWA
guish between nanoscale and larger particles. The 2006
3 for respirable chrysotile fibers is 0.1 fibers per cubic centime-
ACGIH 8-hour TWA for titanium dioxide is 10 mg/m,as
tre; 0.2 f/cc for respirable refractory ceramic fibers; and 1 f/cc
“total”dust.Becausenanoscaletitaniumdioxideismorepotent
for glass wool fibers. Some organizations apply an 8-hour
(due to increased surface area) than larger sized titanium
3 TWA occupational exposure limit of 1 f/cc for respirable
dioxide,NIOSHhasproposeda10-hourTWAof0.1mg/m for
carbon fibers; however, CNTs are distinct from carbon fibers,
ultrafine titanium dioxide (19). However, findings by Warheit
which are not single molecules but strands of layered graphite
et al. on nanoscale titanium dioxide rods and dots run counter
sheets.
to the postulation that, because of increased surface area,
(3) Surface Area—Donaldson et al. indicates that CNT
nanoscale titanium dioxide will always have increased toxicity
number concentration, alone, may not be a suitable metric, and
compared to larger sized particles of similar composition (20).
that a surface area metric might be more appropriate (9).
Additionally, crystalline structure may make a difference in
(4) Trace Contaminants—Trace contaminants may include
toxicity.Forinstance,anatasenanotitaniumdioxidewasfound
organics (such as carbon black and polycyclic hydrocarbons)
to be 100-times more cytotoxic than rutile nano titanium
and metals. Cobalt, iron, nickel, and molybdenum are the most
dioxide leading Sayes et al. (21) to conclude that size as a
commonly used metals in CNT synthesis (9). TheACGIH has
parameter was far less important than the crystal phase
establishedoccupationalexposurelimitsforthesemetalsbased
composition of titanium dioxide. Warheit et al. indicates that it
upon either the inhalable fraction, the respirable fraction, or as
remains to be determined whether similar results reported by
“total dust” (1). It is conceivable that, in the future, theACGIH
Sayes et al. will be measured under in vivo conditions (20).
may have exposure limits for some metals that are based upon
7.2.1.3 Carbon Nanotubes (CNT)—The 2006 ACGIH
the thoracic deposition fraction.
8-hour TLV-TWA for carbon black is 3.5 mg/m , as “total’
8. Exposure Assessment and Exposure Risk Evaluation
dust. Carbon black is composed of disordered graphite sheets
NOTE 2—The specific elements of an exposure minimization program
and differs from the continuous graphitic sheet nature of the
(for example, engineering and administrative controls, work practices and
nanotube surface. The 2006 ACGIH 8-hour TLV-TWA for
any personal protective equipment) should be determined based upon the
respirable graphite (all forms except graphite fibers) is 2
assessment of the potential UNP physical or health hazards outlined in
mg/m . The appropriateness of applying the carbon black or Section 7, and the assessment of potential occupational exposure outlined
in Section 8.
graphiteoccupationalexposurelimitsforcarbonnanotubeshas
been questioned (9, 22, 23). With regard to carbon nanotubes,
8.1 Potential UNP Exposure Routes—As with other
occupational exposure limits for mass, number, and surface particles, workers may potentially be exposed to UNP by way
area might be considered. There may also be trace contami-
of inhalation, ingestion, injection and dermal contact (includ-
nants that may be present and the specific occupational ing eyes and mucus membranes).
exposure limits for these contaminants may need to be
8.1.1 The most common route of exposure to UNP in the
considered, as well. workplace is anticipated to be by inhalation.
(1) Mass—Some forms of Single Wall Carbon Nanotubes
8.1.2 Ingestion can occur from unintentional hand to mouth
(SWCNT) have been found to be as toxic as quartz on a mass transfer of materials; ingestion may also accompany inhalation
basis (22, 23), which have lead some to recommend applying exposurebecauseparticlesthatareclearedfromtherespiratory
occupationalexposurelimitsforcrystallinesilica(forexample, tract may be swallowed.
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8.1.3 Some studies suggest that UNP could also enter the risk of UNPexposure.Assessments should be repeated prior to
body through the skin or eyes during occupational exposure. the start-up of a new task or operation, prior to the re-start of
Research is ongoing to determine whether this is a viable a task or operation following a change, periodically even in the
exposure route for UNP (7). absence of changes in accordance with 6.6, and any other
circumstances where the exposure potential needs to be con-
8.2 The nature and extent of any UNP exposure will be
firmed or reestablished.
dependent on the physical characteristics of the material.
8.5 Quantitative Exposure Assessments:
8.2.1 Solids—Handling of solid materials (for example,
8.5.1 Quantitative UNP exposure measurements may be
nanocomposites) where UNP are bound on or within a solid
useful for a variety of occupational health and system safety
matrix should pose no risk of exposure during normal han-
purposes including (a) evaluating UNP metrics against stan-
dling; however, machining, or combustion of such materials
dards for analogous materials, (b) qualitatively assessing the
may or may not generate UNP. Like deposition of other types
effectiveness of containment controls, work practices, or the
of ultrafine airborne particles, nanoscale particle agglomerates
effect of changes to processes or controls; (c) identifying
greaterthan500nmindiameteraredepositedintherespiratory
sources, patterns and direction of releases, distributions of
tract according to their aerodynamic equivalent diameter
exposure, (d) and estimating exposure levels as a function of
(AED) (24), which is a function of the particle density, shape,
process.
and diameter (6). Diffusion is the predominant deposition
8.5.2 Technical Constraints—Quantitative and qualitative
mechanism in the respiratory tract for UNP and nanoscale
assessment of potential UNP exposure in occupational setting
particle agglomerates <500 nm in diameter and is governed by
presents a number of technical challenges. In general there is
geometric physical diameter rather thanAED (24). The dustier
no consensus regarding: (a) the relative importance of the
(ability to become airborne) the material, the more it is likely
different exposure metrics that might be used; (b) the best way
to become aerosolized and become inhaled, inadvertently
to characterize and differentiate exposures against available
ingested, or for there to be contact with the skin, eyes, and
metrics; or (c) the best measurement techniques to monitor
mucous membranes.
exposures in the workplace. Depending on the metric selected,
8.2.2 Liquids—UNP suspended in liquids may pose poten-
background concentrations of non-target nanoscale particles
tial exposure risks, including inhalation, ingestion or skin
may significantly interfere with obtaining relevant and mean-
absorption if suspensions are either physically contacted (skin,
ingful results, and it may not be possible to control for this
eye, or mucous membrane) or if the suspensions are aero-
interference. The direct and indirect sampling and analysis
solized and subsequently inhaled.
techniques and the commercially available instruments for
8.3 Inventory of Potential Exposure Locations—The expo-
measuring airborne nanoaerosols vary widely in complexity,
sure assessment should begin with assembling a complete
accuracy and selectivity depending on the metric to be as-
inventory of work processes and activities where the potential
sessed.
for exposure to UNP may reasonably be expected to exist.
8.5.3 Appendix X2 and Refs (7, 25-32) provide additional
Relevant activities at a facility may include material receipt
guidance for employee and workplace UNP aerosol exposure
and unpacking; all manufacturing and finishing processes; lab
assessments.
operations; storage, packaging and shipping; waste manage-
8.6 Exposure Assessment for Materials and Devices Con-
ment activities; maintenance and housekeeping activities; rea-
taining Bound Engineered Nanoscale Particles:
sonablyforeseeableupsetcircumstances;andothermovements
8.6.1 Devices, such as integrated circuits, that contain
of goods and employees in and out of UNPwork areas. Annex
bound, engineered nanoscale particles or nanoscale features
A2 provides additional guidance for identifying specific pro-
pose a minimal risk of releasing UNP during handling.
cesses and operations that may be a source of UNP and may
Likewise, large-scale composite articles which contain na-
present a risk of occupational exposure by inhalation,
noscale particles typically do not present significant exposure
ingestion, or dermal penetration, or a combination thereof.
potential as the nanoscale particles are bound within the matrix
8.4 Qualitative Exposure Assessments—A qualitative as-
of the composite.Absent reason to believe that these materials
sessment of the potential for direct and indirect occupational
shed UNP at the exposed surfaces no precautionary measures
exposuretoUNPshouldbemadeforallphasesofeachactivity
are warranted.
identified in the inventory. The assessment should include full
8.6.2 The risk of UNP exposure from handling or process-
consideration of the properties of the UNP material at the
ing materials containing nanoscale particles is greater,
different process locations, the quantity of material present in
however, if the composite matrix is subject to disintegration in
each process, the design and performance characteristics of
the course of foreseeable use or handling (for example, the
relevant process equipment, any existing engineering controls,
matrix is brittle or disintegrates), or if the materials or devices
and the effect of any existing administrative exposure controls.
are otherwise used or handled in such a manner that that they
The method and results of the assessment should be docu-
may generate UNP (for example, machining, saw cutting,
mented. Appendix X2 provides additional guidance for assess-
drilling, or grinding). The user should evaluate the use of
ing UNP exposure risk.
materials containing nanoscale particles for their potential to
8.4.1 For new operations, exposure assessments are ideally release UNP in the course of reasonably foreseeable use and
performed at the pre-design stage so that facilities and process handling. This evaluation should be based on information
may be designed and constructed to present an inherently low provided by the supplier or manufacturer and the user’s
E2535 − 07 (2018)
circumstances of use or processing of the nanoscale particle designed to collect nanoscale particles in well-adapted liquids
containing material. If the result of the assessment indicates a or dust suppression mists to minimize particle releases may be
significantriskthatUNPmaybegeneratedorreleased,thenthe utilized.
user should establish work practices to minimize UNP expo-
9.3.3 Waste Minimization Strategies—Processes may be
sureconsistentwiththescaleoftherelevantoperationsandthis
designed and optimized to minimize the quantity of UNP-
guide.
containing waste generated.
9.3.4 Ventilation Strategies:
9. Exposure Minimization Methods
9.3.4.1 Removing UNP from workplace air by well engi-
9.1 Generally—This section of this guide provides informa-
neered ventilation systems is an effective and important
tion and guidance concerning a variety of exposure control method for minimizing the potential for inhalation of UNP.
methods potentially available to the user. Not all of the noted
Ventilation systems should be designed, tested, and maintained
control methods will be relevant or necessary to meet control
using applicable guidance (for example, Refs (33-37)). Current
objectivesatagivenfacility.See1.2.Refs (7)and (29)provide
scientific knowledge regarding the generation, transport, and
additionalguidanceregardingexposureminimizationmethods.
capture of a
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