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Title: Technical Assistance for Development of Regional Laboratories of Occupational Health Safety Centre (

Technical Assistance for Development of Regional
Laboratories of Occupational Health Safety Centre
This project is co-funded by the European Union
and the Republic of Turkey
  • EuropeAid/127200/D/SER/TR

Occupational Exposure Limits, other reference
values and interpretation of measurement results
This project is co-funded by the European Union
and the Republic of Turkey
  • Jan Gromiec, Ph.D.

  • On completion of this course, participants
  • fully understand the meaning of different types
    of Occupational Exposure Limits
  • be acquainted with the procedures and the
    rationale for OEL derivation at the EU and
    national levels
  • be acquainted with exposure assessment criteria
    in the USA
  • have a knowledge on a possible role of DNELs
    (Derived-No-Effect-Levels) as the criteria of the
    assessment of the occupational exposure to
  • be able to interpret measurement results

The course outline
  • Basic terms and definitions related to
    Occupational Exposure Limits (OEL)
  • OELs in the European Union
  • OELs in individual EU countries
  • Procedures of OEL setting
  • OELs in the USA (OSHA, ACGIH, NIOSH)
  • Derived-No-Effect Levels (DNELs)
  • Comparison of OELs and DNELs
  • Interpretation of measurement results
  • Calculation of uncertainties

Occupational Exposure Limit (OEL)
  • Occupational exposure is a measure of the
    intensity and/or extent to which the human body
    experiences a particular hazard.
  • Quantitative health standard, expressed as a
    mean concentration over a given period of time,
    which an air pollutant must not exceed if the
    exposed workers health is not to be affected.

Limit value (old term)
  • Reference figure for the concentration of a
    chemical in air
  • NOTE
  • set for reference periods of 8 h
  • temperature of 200C
  • pressure of 101,3 kPa.
  • The limit values for suspended matter are given
    in mg/m3 or multiples of that for actual
    environmental conditions (temperature, pressure)
    at workplace. The limit values of fibres are
    given in fibres/m3 or fibres/cm3 for actual
    environmental conditions (temperature, pressure)
    at workplace.
  • (EN 6891995)

  • The effects of increasing exposure to chemical
    substances may be viewed as a continuum  
  • (1) no effects observed  
  • (2) compensatory effects or early effects of
    dubious significance without adverse
  • health consequences  
  • (3) early health impairment (clear adverse
  • (4) overt disease, possibly death.

  • As with systemic health effects, responses to
    irritants may be viewed as a continuum
  • 1) no effects observed no awareness of exposure
  • 2) very slight effects awareness of exposure  
  • (3) slight irritant effects or nuisance (e.g.
    smell) easily tolerable
  • (4) significant irritation/nuisance, overt health
    effects barely tolerable
  • (5) serious health effects (e.g. pulmonary
    oedema) intolerable

To convert ppm to mg/m3
  • OEL in mg/m3
  • OEL in ppm

Objectives of OEL setting
  • to prevent or limit the exposure of workers to
    dangerous substances at workplaces
  • to protect the workers that are likely to be
    exposed to these substances
  • OELs began to be established in order to provide
    criteria on the basis of which decisions could be
    made as to whether the airborne concentrations of
    given substances were sufficiently low to prevent
    adverse effects on health.
  • OELs may be used for a number of purposes. to
    provide standards or criteria against which
    measured exposure levels in existing workplaces
    may be compared in order to ensure that
  • They may also be used for design purposes

OELs at the EU level legal aspects
  • Council Directive 80/1107/EEC (amended by
    Directive 88/642/EEC) setting out measures for
    the control of risks related to chemical,
    physical and biological agents
  • Council Directive 90/394/EEC provisions for
    setting up limit values for carcinogens
  • Framework Directive 89/391/EEC measures to
    encourage improvements in the safety and health
    of workers at work
  • Council Directive 98/24/EC legal basis for
    Community OELs
  • Commission Directive 2000/39/EC establishing the
    first list of indicative OELs

Scientific Committee for Occupational Exposure
Limits to Chemical Agents (SCOEL)
  • Set up by the European Commission Decision
    95/320/95 of 12 July 1995
  • to supply the Commission with opinions at the
    latters request on any matter relating to the
    toxicological examination of the chemicals for
    their effects on health of workers.
  • to give in particular advice on the setting of
    OELs based on scientific data and where
    appropriate propose values which may include
  • - the eight-hour time weighted average (TWA)
  • - short-term limits/ excursion limits (STEL)
  • - biological limit values

Steps leading to the establishment of EU OELs
  • Preparation of a scientific dossier for review
  • Evaluation of a scientific dossier
  • Development of recommendation from the SCOEL
    (scientifically based OEL) for the Commission
  • Development of a proposal for an OEL by the
    Commission services
  • Consultation of the Advisory Committee for
    Safety, Hygiene and Health Protection of Workers
  • Adoption of the implementing Directive

General procedure for setting OEL proposals by
  • Assemble all available data on the hazards by the
  • Determine whether the database is adequate for
    the setting of an OEL
  • Identify the adverse effects due to exposure to
    the substance
  • Establish which adverse effect(s) is (are)
    considered to be crucial in deriving OEL
  • Identify the relevant studies which characterise
    these key effects (quality of of these studies)
  • Establish whether the substance acts via a
    non-threshold or threshold mechanism (crucial
    for health based OELs)

Indicative Occupational Exposure Limit Values
(IOELs) Commission Directive 2000/39/EC
  • Definition Indicative OELs are numerical values
    which provide the threshold level of exposure to
    a given substance below which no detrimental
    effects to workers health are expected.
  • Indicative OELs may be established in those cases
    where a review of the total available scientific
    data base leads to the conclusion that it is
    possible to identify a clear threshold dose below
    which exposure to the substance in question is
    not expected to lead to adverse effects

Indicative Occupational Exposure Limit Values
(IOELs) Commission Directive 2000/39/EC, cntd
  • For any chemical agent for which indicative
    occupational exposure limit values are
    established at Community level, Member States are
    required to establish a national occupational
    exposure limit value, taking into account the
    Community limit value, determining its nature in
    accordance with national legislation and practice
  • Indicative occupational exposure limit values
    should be regarded as an important part of the
    overall approach to ensuring the protection of
    the health of workers at the workplace, against
    the risks arising from hazardous chemicals

Short-term Indicative OEL
  • A limit value above which exposure should not
  • occur and is related to a 15-minute period,
  • unless otherwise specified
  • (COMISSION DIRECTIVE 2000/39/EC of 8 June

  • Short-term exposure limits - peak limitations,
    intended as supplementary to TWA and protecting
    against short-time effects like annoyance,
    irritation, CNS depression etc. in situations
    where OEL-TWA values were set at levels only
    slightly lower than the concentrations associated
    with the risk of short-term exposure effects.
  • The definition stresses that STEL is not a
    ceiling value, the essential difference being
    that no reference period is quoted for the
    ceiling concentration. It should be noted,
    however, that among the already published 90
    indicative OEL values none refers to the ceiling

Binding Occupational Exposure Limits Values
  • for some adverse effects (genotoxicity,
    carcinogenicity, respiratory sensitization) it
    may not be possible on present knowledge to
    define a threshold of activity
  • pragmatic OELs are established at levels of
    sufficiently low risk
  • adopted by the Council of Ministers of the
    European Communities under the procedure laid
    down in Article 118a of the Treaty. Such limit
    values reflect scientific data as well as
    socioeconomic considerations and must be
    transposed into national legislation as minimum
  • if for a given substance the binding OEL has been
    established, the Member States are obliged to
    introduce into national legislation a limit
    value for this substance, not exceeding the
    agreed BOEL

EC law on Occupational Safety and Health (OSH)
  • EC OSH Directives contain only minimum
    requirements. During the necessary
    transposition into national legislation more
    stringent provisions than laid down in the EC
    Directives can be introduced by the Member
  • Legal bases 137 Article of the EC-Treaty

Occupational Exposure Limits in Poland
  • Maximum Admissible Concentration (MAC)
  • Proposed by the MAC Commission, established by
    the Minister of Labour and Social Policy
  • Starting point
  • -NOAEL or LOAEL for substances with systemic
  • activity
  • -human data or RD50 for irritants
  • Use of uncertainty factors
  • Ceiling MACs for substances highly irritating or
    dangerous to life
  • STEL (2x15 min. during a workshift)
  • Analytical method required
  • Conservative and restrictive approach

System of setting MAC-values in Poland
Maximum admisible concentrations
Biological tolerance limits Medical preventive
Methods of air sampling and analysis
Legislation level
requirement for MAC proposal
Preparatory level
Intersectoral Commission for MAC and MAI Values
Group of Experts for Chemical Agents
MAC documentation
Calling for information
demand for MAC-value
  • Bank of information
  • exposure data
  • health effects data
  • Industry
  • Health administration (sanitary inspection)
  • Labour administration
  • State Labour inspection
  • Trade unions
  • Research institutes

Number of OELs in Poland, Germany and USA
  • original bibliography collected through the data
  • available documentations on exposure limits in
    other countries (USA, Germany, Sweden, EU)
  • WHO Environmental Health Criteria
  • IARC evaluation of the carcinogenic risk due to
  • other reviews
  • unpublished documented data

MAC Documentation Content
  • Dose-effects and dose-response relationships
  • Bases for existing MAC-values and biological
    tolerance limits
  • Bases for proposed MAC-values and biological
    tolerance limits
  • Methods of determination in the air and in
    biological material
  • Pre-employment and periodical examinations -
    expsoure contraindications
  • References
  • Summary
  • Substance characterization, uses and occupational
  • Toxic effects on man
  • Toxic effect on experimental animals
  • Carcinogenicity, mutagenicity, teratogenicity,
    embryotoxicity and effects on reproduction
  • Toxicokinetics
  • Mechanisms of toxicity
  • Combined effects

The theoretical fundamentals for setting hygienic
standards comprise
  • results of epidemiological studies of a
    relationship between the magnitude and duration
    of exposure and the induced health effects
  • results of medical observations of workers
    exposed to given toxic agent under industrial
  • results of experimental animal studies.

Calculation of a MAC value
Calculation of a MAC value for a chemical
substance MAC NOAEL/UF or LOAEL/UF Uncertaint
y factor, UF, is calculated from the formula UF
A x B x C x D x E, where FACTOR EXTRAPO
LATION A max. 2 average human to sensitive
human (intraspecies) B max. 10 for tests using
exposures other than inhalation max. 3 for
tests using inhalation exposure (interspecies) C
max. 3 short term to long-term exposure D
max. 3 LOAEL to NOAEL E max. 5 modifying factor
(depending on experts opinion on the
completeness of data and for potential long-term
Calculation of a MAC for irritant substances
Calculation of MAC values from RD50
data Calculation of a MAC value for the
irritating substances is based on RD50 value,
representing the concentration that induces a 50
reduction of the respiratory rate in experimental
animals. MAC is selected in the range from 1/10
to 1/100 of the RD 50 value. TABLE
Calculation of MAC values from RD50 data
Other MAC related issues
  • number of MAC chemicals in Poland 511, capacity
    to produce 20 documentations/yr
  • number of 10 t/yr MAC chemicals 834 (2004), most
    of them having MAC value assigned
  • quality of OELs expert assessment, multilevel
    process, transparency
  • no tradition of private OELs in Poland
  • need for analytical methods to determine
  • compliance

Limit values in the USA
  • ACGIH Threshold Limit Values (TLV)
  • OSHA Permissible Exposure Limits (PEL)
  • NIOSH Recommended Exposure Limits (REL)

  • The longest tradition is behind the hygienic
    standards published by ACGIH? under the
    registered name of Threshold Limit Values
    (TLVs?), and annually updated since 1946. The
    TLVs? are not obligatory under current US legal
    regulations nevertheless, in view of the high
    ACGIH? reputation, they serve as an important
    guide on the recommended limits of occupational
    exposures not only in the USA but also in other
  • TLV-TWA (Threshold Limit Value - Time-Weighted
    Average) is defined as the time-weighted average
    concentration for a conventional 8-hour workday
    and a 40-hour workweek, to which it is believed
    that nearly all workers may be repeatedly
    exposed, day after day, without adverse health

ACGIH TLVs, cntd
  • TLV-STEL (Short-Term Exposure Limit) this is
    defined as a 15-minute TWA exposure which should
    not be exceeded at any time during a workday,
    even if the 8-hour TWA is within the TLV-TWA,
    Exposures above the TLV-TWA up to the TLV-STEL
    should not be longer than 15 minutes and should
    not occur more than four times per day. There
    should be at least 60 minutes between successive
    exposures in this range.
  • TLV?-Ceiling represents a value of concentration
    absolutely not to be exceeded at any moment.
  • The ceiling values refer mostly to irritant
    gases, and for that type of chemical substances
    they are the only applicable hygienic standards
    (no TLV?-TWA are available).

ACGIH TLVs, cntd
  • Individual susceptibility
  • Hypersensitivity
  • Procedures and process of setting TLVs
  • Health based criteria
  • TLV documentations

OSHA PEL values
  • OSHA was established in 1970 by the US Congress
    as an institution subordinated to the Ministry of
    Labor and entrusted with the task of developing
    and enforcing a law on the health and safety of
    workers . The law is understood as providing also
    for the hygienic standards, which should
  • in the most suitable and practicable way, using
    the best available proof, ensure that none of the
    workers suffers health loss or reduction of the
    physiological parameters even when regularly
    exposed to that agent at the level specified by
    the relevant hygienic standard throughout his/her
    whole working life

OSHA PEL values establishment
  • history of PEL establishment
  • interpretation in U.S. Supreme Court rulings
  • a conservative approach encumbered with the risk
    of an error to the benefit of the worker to
    ensure that steps to be undertaken ensure
    excessive rather than insufficient protection to
    the concerned worker
  • PEL values should be based on the most recent
    scientific data
  • the results of research and recommendations
    prepared mainly by OSHA and NIOSH as the
    starting point
  • clinical observations (accidents, poisonings,
    pathologies), epidemiological data and animal
    test results used as the so-called
    toxicological proof.
  • NOAEL or LOAEL usually employed as a starting
  • uncertainty factors for individual human
    variability, inter-species differences,
    incomplete data on the chronic toxicity, and the
    use of a LOAEL value instead of a NOAEL value
  • seting STEL and Ceiling values (definitions and
    interpretation identical like in case of ACGIH

OSHA PEL values establishment
  • proposals for setting new, or modifying the
    existing PEL values, together with the reasons
    justifying the new or revised standard published
    in the Federal Register as a Notice of Proposed
  • the interested parties (representatives of
    industry, employers, workers, federal agencies,
    scientific institutions, etc.) may present their
    comments and suggestions in writing
  • public hearing of the authors of the proposals by
    the representatives of the commenting
  • the participants present in writing arguments
    for, and against, the proposed standard in
    question. OSHA analyses all the notes, sets PEL
    values and publishes in the Federal Register the
    full text of the documents justifying the new or
    modified PEL value.

OELs in Russia
  • Maximum Allowable Concentartions (MAC) started in
    early 20s.
  • Numerical values much lower than elsewhere, based
    on the concept of the threshold hazardous
    effect and set at the level, that was supposed
    to correspond to a tissue burden in exposed
    subjects which represent the minimum dose that
    triggers changes beyond the limits of
    physiological adaptation reactions.
  • Now under the auspices of the Ministry of Health
    (National Commission on Occupational Exposure
  • Based entirely on toxicological data, without
    reference to occupational hygiene or epidemiology
    (the material derived mostly from Russian
    sources the existing exposure levels in
    industry, technical feasibility and economic
    implication not taken into account.

OELs in Russia, cntd
  • Generally considered to be the ceiling values,
    time weighted average concentrations are
    established for those substances that are highly
  • In most cases established during the Soviet
    period, when the philosophy of hygienic standard
    development was quite different from that in
    other countries and a high coefficient of safety
    was usually applied.
  • The implementation of these standards not as
    strict as required.
  • Not revised and still used in practice despite
    the policy changes and other significant changes
    in socio-economic structure.

OELs for carcinogens
  • effective toxicity threshold does not exist or is
    impossible to be determined each exposure to
    carinogenic genotoxic agent is assumed to be
    associated with the risk of cancer development.
  • not possible to determine the level of the
    substance concentration which does not produce
    adverse health effects in all the exposed
    individuals (a condition specified by most
    occupational exposure limit definitions)
  • for such substances the concentrations should be
    kept as low as possible (if their complete
    elimination from the production process is not
  • legally binding exposure limits take into
    consideration the socio-economic factors and are
    based on the concept of acceptable cancer risk

OELs for carcinogens, cntd
  • OELs for carcinogenic substances are based on the
    data on the carcinogenicity of a specific
    substance in humans (epidemiological data) and/or
    experimental animals.
  • Such limit may be derived from the data on unit
    risk or from the slope factor of the
    dose-response curve in both cases the acceptable
    risk serves as the criterion .
  • In general, in the occupational setting, the
    acceptable levels of cancer risk vary between
    10-2 to 10-5

Classification of carcinogens
  • Classifications referring mainly to the strength
    of proof of their carcinogenic activity (IARC,
    ACGIH, EU Directive 2004/37/EC).
  • In most cases the substances and technological
    processes are classified as
  • carcinogenic to humans,
  • suspected of being carcinogenic to humans,
  • carcinogenic to experimental animals,
  • not classifiable as a human carcinogen,
  • not suspected as a human carcinogen.
  • In some countries information on cancerogenity
    and/or mutagenicity included in the OEL list.

Human Health Hazard Assessment (REACH legal text)
  • REACH (Annex I, 1.0.1 ) defines the Derived No-
    Effect Level (DNEL), i.e. the level of exposure
    above which humans should not be exposed.
  • In the risk characterisation, the exposure of
    each human population known to be or likely to
    be exposed is compared with the appropriate
  • The risk to humans can be considered to be
    adequately controlled if the exposure levels
    estimated do not exceed the appropriate DNEL

Derived No Effect Level (DNEL)
  • Required for 10 tonnes/yr chemicals
  • The purpose of DNELs is to act as the reference
    value for determining adequate control of
    exposure for specific scenarios
  • DNELs (inhalation) for occupational exposure
    comparable to MACs

Steps of DNEL derivation
  • Collection of all available toxicity data
    gathering typical dose descriptors
  • Decision on mode of action threshold vs.
  • Selection of relevant dose descriptor(s) for the
    endpoint concerned
  • Modification of the dose descriptor to the
    correct starting point
  • Application of assessment factors, where
    necessary for the relevant exposure pattern
  • Selection of the critical effect

Dose descriptors for DNEL derivation
  • NOAEL (no observed adverse effect level)
  • NOAEC (no observed adverse effect concentration)
  • LOAEL/LOAEC (lowest observed adverse effect
  • Other dose descriptors (BMD, LD50, LC50, T25
  • All available hazard information needs to be
  • (physical and chemical properties,
    epidemiological data,
  • human data, acute and chronic activity, local and
  • effects etc.)

Modification of dose descriptorsinto the correct
starting point
  • correction for difference in bioavailability for
    the same exposure route
  • correction for different exposure routes
  • correction for difference between experimental
    and exposure conditions
  • correction for differences in respiratory volumes
    between experimental animals and humans

Correction for difference between experimental
and exposure conditions
  • repeated animal inhalation experiment usually 6
  • occupational exposure usually 8 hr/d
  • general population exposure 24 hr/d
  • effects of exposure dependant on dose,
    concentration or both?

Assessment factors (AF)
  • Assessment factors are numerical values used to
    address differences between experimental data and
    the human situation taking into account the
    uncertainties in the extrapolation procedure and
    the available data set
  • Substance-specific information should be used in
    the establishment of appropriate values for the
    various assessment factors
  • In the absence of substance-specific or analogous
    data use default assessment factors
  • It should be remembered that the default
    assessment factors are based on experience and
    not strictly on science and they may or not may
    be not suitable for a given substance

Default assessment factors (AF)
Assessment factor Assessment factor Systemic effects Local effects
Interspecies -differences in metabolic rate per body weight -remaining differences AS 2,5 - 1 (2,5 metab.)
Intraspecies -worker -general population 5 10 5 10
Exposure duration -subacute to sub/semichronic -sub/semichronic to chronic - subacute to chronic 3 2 6 3 2 6
Dose/response -reliability of dose/response, LOAEL/NOAEL, severity of effects 1 (NOAEL) 3-10 (LOAEL) 1 (NOAEL) 3-10 (LOAEL
Quality of database completeness and consistency of available data 1 deviations are possible Quality of database completeness and consistency of available data 1 deviations are possible Quality of database completeness and consistency of available data 1 deviations are possible Quality of database completeness and consistency of available data 1 deviations are possible
Quality of the database
  • thorough analysis of available data
  • lacking data (long-term effects)
  • experimental conditions, quality of animals,
    control groups, etc.
  • consistency of data
  • For experiments carried out according to GLP
  • procedures and complete data, default
  • assessment factor is 1, in other cases expert
  • judgement

Calculation of a DNEL value
  • The overall assessment factor is obtained by
  • multiplication of individual assessment factors
  • Endpoint specific DNEL
  • Care should be taken to avoid double
    counting several aspects when multiplying the
    individual factors

No threshold substances
  • Cancerogenic and mutagenic substances cat. I and
  • DMEL (derived minimal effect level)
  • DAEL (derived accepted effect level)
  • Accepted risk of occupational cancer 10-5 to

2-isopropoxyethanolNOAEC128 mg/m3 (28 days)
  • DNEL
  • Interspecies 1
  • Intraspecies 5
  • Acute/chronic 6
  • NOAEL 1
  • Quality of data 1?
  • DNELinhal
  • MAC
  • Interspecies 1
  • Intraspecies 2
  • Acute/chronic 3
  • NOAEL 1
  • Quality of data 1
  • MAC

2,2-iminodiethanol (DEA)NOAEL 20 mg/kg (13
  • MAC
  • Interspecies 2
  • Intraspecies 2
  • Subchronic 2
  • NOAEL 1
  • Quality of data 2
  • NOAEC 20x70/10 140 mg/m3
  • MAC
  • mg/m3
  • DNEL
  • Interspecies 4x2,5
  • Intraspecies 5
  • Subchronic 2
  • NOAEL 1
  • Quality of data 2?
  • DNELoral
  • DNELinhal 0,1 mg/kg/dx70/10
  • 0,7 mg/m3

ChloroethanNOAEL 26 800 mg/m3 (13 weeks)
  • MAC
  • Intraspecies 2 Interspecies.2
    subchronic/chronic 2
  • NOAEL/LOAEL 1 Quality of data 4.
  • MAC
  • Value 200 mg/m3 has been established since IOEL
    is 268 mg/m3
  • DNEL
  • Interspecies 2,5 Intraspecies 5
    Subchronic/chronic 2
  • NOAEL/LOAEL 1 Quality of data 4?
  • DNELinhal

Roles of OELs and DNELs
assessment of occupational exposure (compliance)
1 risk characterisation under REACH
exposure/DNEL 1
OELs and DNELs similarities
  • the same objective, in general concentration,
    that would not result in health impairment due to
  • the same starting point, though assessment
    factors are different

OELs and DNELs differences
  • OELs are developed strictly for OSH purposes and
    have direct application as a reference tool for
    the systematic monitoring of exposure
  • DNELs primarily not intended for OSH purposes but
    as a tool for chemical safety assessment and
    selection of proper RMM
  • DNELs have no direct impact on workplace

OELs and DNELs differences, cntd.
  • OELs are legally binding (responsibility of the
    Government) legal instrument of enforcement of
    health policy, compliance supervised by
    governmental agencies or institutions
  • DNELs introduced by companies only
  • Representativeness and transparency of the OEL
    establishment process lack of expert judgement
    in the DNEL derivation
  • Different assessment factors mostly default
    factors in DNELs vs expert judgement in OELs

Conclusion of the occupational exposure
assessment in EN 689
  • The occupational exposure concentration is the
    arithmetic mean of the measurements in the same
    shift with the appropriate reference period of
    the OEL value of the agent of consideration. In
    the case of varying averaging times this can be
    accounted for by time-weighting the values
    (examples in Annex B).
  • A number of schemes can be devised to compare
    exposures with the OELs (Annexes C and D).
    Whatever scheme is used, one of the three
    following conclusions shpuld be made
  • the exposure is above the limit value the reason
    should be identifiedand appropriate measures to
    remedy the situation should be implemented as
    soon as possible.The occupational exposure should
    be repeated
  • The exposure is well below the limit value and is
    likely to remain so on the long-term basis due to
    the stability in the working conditions and the
    arrangement of the work process. In this case
    periodic measurements are not needed. Regular
    check is, however, required whether the
    conditions at workplace are unchanged.
  • The exposure do not fit into categories (a) or
    (b). Here, even though exposure may be below OEL,
    periodic measurements are still required.

When the exposure may be considered acceptable
  • Time weighted average (TWA) concentration is
    below or equal to OEL.
  • Short term concentration (15 min) is below or
    equal to STEL
  • The sum of the ratios of concentrations of
    individual compounds to their OELs must be less
    than or equal to one

Calculation of the occupational exposure
concentration from individual analytical values
(Anex B)
  • This procedure only applies, when OEL has been
    set as an 8-hr TWA
  • The term 8-hr reference value period relates to
    the procedure whereby the occupational exposures
    in any shift period are treated as equivalent to
    a single uniform exposure for 8hr
  • The 8-hr TWA may be represented mathematically by

Examples of calculations (Annex B)
  • The operator works for 7 h 20 min on a process in
    which he is exposed to a substance with an OEL.
    The average measured concentration during that
    period is 0.12 mg/m3

Examples of calculations, cntd (Annex B)
Working period Exposure mg/m3 Duration of sampling, hr
08.00 bis 10.30 0,32 2,5
10.45 bis 12.45 0,07 2
13.30 bis 15.30 0,20 2
15.45 bis 17.15 0,10 1,5
Examples of calculations, cntd (Annex B)
Working period Task Exposure mg/m3 Time, hr
07.30 to 08.15 Setting up zero 0,75
08.15 to 10.30 Product run1 5,3 2,25
10.30 to 11.00 Break zero 0,50
11.00 to 13.00 Product run2 4,7 2,00
13.00 to 14.00 Lunch zero 1,00
14.00 to 15.45 General tidying 1,6 1,75
15.45 to 16.00 Break zero 0,25
16.00 to 19.00 Extra product run 5,7 3,00
Examples of calculations, cntd (Annex B)
  • A worker is engaged in a dusty process in a
    factory which is running at a maximum production.
    He agrees to work his machine an additional 3h on
    one day to complete some orders. Total shift
    length is 11,5 h.
  • The 8-hr TWA
  • Without additional 3 hr exposure

Probability plot (Annex G)
  • This approach is the percentile method of
    expressing exposure measurements, which uses a
    statistical analysis of the data in the form of
    lognormal probability or cumulative frequency
  • To construct a lognormal probability plot
  • Rank exposure data from rhe lowest to the
  • Count the number of results and obtain the
    appropriate plotting positions as shown in the
    examples in tables G.1, G.2. and G.3 of Annex G.
  • Select log probability graph paper having a
    Y-axis capable of covering the range of the
    exposure data.
  • Plot each exposure value against the
    corresponding plotting point on the log
    probability paper, as shown in figure G.2 for the
    raw data in table G.3.

Probability plot (Annex G), cntd
  1. Fit the straight line to the data points,
    disregarding all points outside the bounds of 1
    and 99 probability. For all remaining data give
    preference to those nearest the central 50
    position, that is in the 20 to 80 region
  2. If the data do not follow the straight line then
    the underlying distribution may not be
    lognormally distributed, or may comprise more
    than one sample population
  3. The geometric mean value is the 50 probability
    value and may be read directly from the
    intersection of the fitted line with the 50
    probability line
  4. The geometric standard deviation (GSD) is the
    slope of the lognormal plot and a measure of
    variability or dispersion of the data

Example of a probability plot (EN 689, Annex G
Probability plot (Annex G), cntd
  • The geometric standard deviation is given by
  • The GSD can, together with the geometric mean be
    used, if required to draw the theoretical best
    fit line for the data.
  • Good for extrapolation to higher exposure levels
    or probabilities
  • Two statistical parameters characterise lognormal
    probability plot
  • -the geometric mean (50 of results are below and
    above the value)
  • -the GSD (the slope of the cumulative exposure
    plot (measure of variability of the results).
  • The plot can be used to compare exposure data
    with OEL at any probability level, or to estimate
    the percentage of exposures likely to exceed a
    particular value.
  • Normally not less than 7 data points are required
    for such comparisons or estimates.

Evaluation of the occupational exposure in EN
689, Annex C
  • Concentration is devided by OEL to obtain I (the
    subtance index)
  • I C/OEL
  • For the results below LOD, ½ should be used.
  • If the index for the first shift is I 0.1,
    exposure is below the limit value. If furhermore,
    it can be shown that this value is representative
    for the long term working conditions the periodic
    measurements can be omitted.
  • If each single index of at least three different
    shifts is I 0.25 exposure is below the limit
    value. If furhermore, it can be shown that this
    value is representative for the long term working
    conditions the periodic measurements can be
  • If the indices of at least three different shifts
    are all I 1 and the geometric mean of all
    measurements is 0.5 then exposure is below the
    limit value.
  • If an index is I gt 1, exposure is above the OEL.
  • In all cases that do not fit into the above the
    procedure leads to no decision.

Evaluation of the occupational exposure in EN
689, Annex C, cntd
  • If any of the conditions of b), c), or d) apply,
    then the occupational exposure assessment can be
  • In the cases c), or d) the concentration can be
    interpreted as the first periodic measurement.
    Its result then may determine the time interval
    for the next periodic measurement.
  • If the workers are exposed simultaneously or
  • consecutively to more than one agent during the
    same workshift, this fact needs to be taken into

Types of Mixture
  • Natural mixtures
  • Petroleum based mixtures
  • Formulated mixtures
  • Processing mixtures
  • Combined mixtures

Natural mixtures
  • Source extraction and/or processing naturally
    occurring substances (mineral ores, vegetable
    oils, tea etc.)
  • Composition may be not known and vary depending
    on source and season
  • Defined by mostly by their physical properties or
    technological processes
  • In most cases no OELs assigned
  • Specific ill-efects usually well documented

Petroleum based mixtures
  • Sub-group of natural mixtures
  • Relates to distillation fractions of oil (white
    spirit, fuels, naphtas etc.)
  • Defined by by physical properties (e.g. boiling
  • Composition may vary depending on origin and
  • The mixture and/or its components may have been
    assignrd OELs

Formulated mixtures
  • Produced by mixing components to a pre-defined
    formula to give products for specific
    applications (paints, adhesives, cleaning
  • The composition is usually known some components
    may be already natural mixtures
  • Composition is controlled
  • No OEL for the mixture, individual components may
    have been assigned OELs

Processing mixtures
  • Arise from the technological processes (plastic
    fumes, welding fumes, rubber fumes etc)
  • Composition changes with process parameters
    (temperature, pressure, oxygen supply etc)
  • Contain both identified and unidentified
  • Some compounds may have or may have not OELs
  • Some of the process mixtures may have been
    assigned OELs

What to measure?
  • All, or many of the individual components
    (require knowledge of the mixture components and
    availability of the appropriate analytical
  • The total mixture (if OEL is for the mixture or
    if the total mixture exposure serves as a measure
    of control)
  • A single substance, as a guide to exposure and

A single substance as a measure of exposure
  • Measurement methods not available for all the
  • Many components without OELs
  • There are unidentified components
  • Quantification of all components would be
    excessively expensive

Selection of the key components to be measured
  • The existence of OELs
  • Concentration in the mixture
  • The toxicity of the individual substances

Categories of possible joint toxic effects
  • Independent action each component acts in an
    individual way in the human body which is
    different from, and unaffected by, the effects of
    other components
  • Additive action - the combined toxic effects are
    the simple sum of toxic effects of each component
    acting alone
  • Synergistic action the combined toxic effects
    are greater than the simple sum of the toxic
    effects of the single components acting alone
  • Antagonistic effect the combined toxic effects
    are less than the simple sum of the toxic effects
    of each component acting alone

Calculation of the additive exposure
  • If the workers are exposed simultaneously or
    consecutively to more than one agent during the
    same work-shift, the sum of the ratios of
    measured exposures for individual exposures (C)
    to their OELs must be less than, or equal to,
    one, according to the formula

Test report
  • Reports shall be written of the occupational
    exposure assessment and
  • of any periodic measurement. According to EN 689,
    the report has to
  • contain
  • the name of the person(s) or institutions
    undertaking the assessment and the measurements
  • the name of the substance considered
  • name and address of company
  • the description of workplace factors including
    the workplace conditions during the measurements
  • the purpose of the measurement procedure
  • the measuring procedure
  • the time schedule ((date, beginning and end of
  • the occupational exposure concentrations
  • all events and factors liable to influence
    appreciably the results
  • details of quality assurance, if any
  • result of the comparison with the limit value

Calculation of the expanded uncertainty
Calculation of the expanded uncertainty, cntd
Uncertainty components in workplace air
measurement methods
  • sampling
  • -uncertainty associated with sampled air volume
  • -uncertainty associated with sampling efficiency
  • -uncertainty associated with sample storage and
    transportation, if
  • any
  • analysis
  • -uncertainty associated with method recovery
  • -uncertainty associated with analytical
  • -uncertainty associated with the calibration
  • -uncertainty associated with instrument drift
  • The uncertainty of each of those components is
    estimated and
  • calculated and then combined to obtain an
    estimate of the
  • uncertainty of the measurement method as a

Sources of uncertainty in pumped sampling
  • Flow rate measurement - the calibration of the
    flow meter (random error), the reading of the
    flow meter (random error) and, where
    appropriate, correction of the flow rate reading
    to ambient pressure and temperature.
  • The uncertainty of flow rate calibration
    should be calculated from the data given on the
    flow meter test certificate. The uncertainty of
    the flow rate reading should be calculated from
    measurements carried out under repeatability
  • Pump flow stability
  • Sampling time

Flow rate measurements
Uncertainty of the flow rate measurement for
different types of flow meters
Flow rate stability
  • Pumps for personal air sampling are usually
    selfregulating and maintain the set flow
    independent of variation in back pressure
  • EN 1232 and EN 12319 require that the flow rate
    is maintained within 5 of the set value
    throughout the sampling period
  • Assuming a rectangular probability distribution,
    the maximum acceptable value for a
    non-randomuncertainty component for the pump flow
    stability is 5/v3

Uncertainty components associated with sampling,
  • Sampling time may be measured very exactly with a
    radio controlled clock, a quartz clock or
    stopwatch. The major source of uncertainty in
    measurement of sampling time is the accuracy with
    which the reading is taken, i.e. to the nearest
    minute or second. The non-random uncertainty
    component is very small in the case of long term
    measurements (e.g. gt 2 h) and can be disregarded,
    but for short term measurements it needs to be
    taken into account.
  • (for a 15 minute sample, if time is recorded
    to the nearest minute, the RSD is 3.8, assuming
    a rectangular probability distribution)

Uncertainty associated with sampling efficiency
  • Influence of ambient conditions (temperature,
    pressure, humidity)
  • Influence of a flow rate
  • Breakthrough volume (EN 1076)
  • Efficiency when sampling with bubblers/impingers
    and impregnated filters

Uncertainty associated with sample storage and
  • Non-random uncertainty component for storage can
    be estimated by analysis of samples collected
    from a test atmosphere or prepared by spiking
    sampling media with a chemical agent. Calculated
    from the difference between the mean results of
    replicate samples analysed immediately after
    sampling/spiking and after the maximum storage
    period specified in the method.
  • Storage tests described in detail in EN 838
    (passive dosimetry) or EN 1076 (pumped methods)
  • No need to take into consideration for gas and
    vapour samples if transported in an appropriate
    manner as specified in the method.
  • The transport of aerosol samples has a component
    of uncertainty associated with material losses
    from the sample substrate or substrate
    contamination The upper limit for the loading of
    the collection substrate can be determined as
    described in EN 838 or ISO15767.

Uncertainty asssociated with analytical recovery
  • May be carried out following the tests described
    in EN 1076 and EN 838 by the use of standard test
  • Results for vapour and gases methods are normally
    corrected for desorption efficiency. It can be
    calculated using spiked sampling media. When the
    influence of ambient conditions and other factors
    are not significant and results are corrected for
    desorption efficiency, only the uncertainty
    component associated with this correction is
    taken into account.

Uncertainty asssociated with analytical recovery,
  • Bias can be estimated from
  • results obtained by analysing a suitable number
    of replicate samples of certified reference
  • results obtained from replicate samples taken in
    the test gas atmospheres
  • results from interlaboratory comparisons
  • results from recovery tests carried out on spiked
    sampling media
  • Desorption efficiency can be calculated from the
    results of replicate analyses of certified
    reference material or of sampling media spiked at
    several levels covering the range of the
    application of the method, dividing the mass of
    analyte recovered by the mass applied, as
    specified in EN 838 and EN 1076.

Desorption efficiency
  • When desorption efficiency does not vary
    significantly with the concentration (general
    case) and the results are corrected for
    desorption efficiency, the random uncertainty
    component associated with this correction is
    estimated and treated as an uncertainty
    component. The random uncertainty component
    associated with incomplete desorption is
    estimated as the relative standard deviation of
    the mean of the desorption efficiencies for all
  • If desorption efficiency correction is not
    applied to the results, the bias component is
    estimated and treated as an uncertainty
    component. The non-random uncertainty component
    associated with incomplete desorption is
    estimated as the difference of the mean of the
    desorption efficiency at all concentrations from
    unity and converted to a standard uncertainty.
  • In some cases desorption efficiency varies with
    concentration. In this case the random and
    non-random uncertainty components will be
    estimated from the function relating the
    desorption efficiency to concentration.

Uncertainty asssociated with analytical
  • In general, the uncertainty associated with
    analytical variability may be estimated either
    from data obtained under repeatability conditions
    or from data obtained under reproducibility
    conditions. When the analytical precision is
    determined from within-laboratory reproducibility
    data, i.e. using quality control data, most
    random and randomized uncertainty components are
  • The uncertainty associated with the analytical
    precision is determined by analysing calibration
    standards of the same composition under
    repeatability conditions. In vapour and gases
    methods this contribution is already incorporated
    in contributions from the determination of the
    desorption efficiency and it does not need to be
    taken into account.
  • If applicable, the random uncertainty component
    associated with blank subtraction, or non-random
    uncertaintycomponent when no blank subtraction is
    performed, need to be included.

General equations for combination of uncertainty
  • To calculate the random and non-random components
    of sampling uncertainty and analytical
    uncertainty, the relevant individual uncertainty
    components are combined according to equations

General equations for combination of uncertainty
components, cntd
-are defined in 6.1
-are the corresponding relevant individual
uncertainty components
-are the corresponding numbers of relevant
individual uncertainty components
Expanded uncertainty requirements for
measurements for comparison with OELs and
periodic measurements
Reference period Measuring range Relative expanded uncertainty
short term (e.g.15 min) 0.5 to 2 times OEL value 50
long-term 0.1 to lt 0.5 times OEL value 50
long-term 0.5 to 2 times OEL value 30
Thank you for your attention
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