International Module W501
Measurement of Hazardous Substances
(including Risk Assessment)
Day 2
Air Sampling Theory & Practice
Confined Spaces
Biological Monitoring
Sample Analysis
Today’s Learning Outcomes
• Receive guidance in understanding the reasons for
any incorrect answers to the overnight questions
from Day 1
• Understand the principles of sampling for airborne
contaminants and be able to use those principles to
devise a suitable sampling strategy
Today’s Learning Outcomes (cont)
• Be familiar with the requirements for monitoring in
confined spaces and understand some of the issues
that need to be considered during this process
• Understand the principles of biological monitoring
and their appropriate application
Today’s Learning Outcomes (cont)
• Be familiar with the various methods that are used to
analyse the various contaminants found in the
workplace
• Understand the requirements to ensure the quality of
laboratory analysis
Topics To Be Discussed
• Review of overnight questions
• Air sampling theory & practice
–
–
–
–
–
Sampling strategies
Survey design
Personal sampling
Area sampling
Surface & other measurements
Topics To Be Covered (cont)
• Confined spaces
• Biological Monitoring
• Sample analysis
Air Sampling Theory & Practice
Air Sampling Theory & Practice
• Workplace sampling strategies
– Strategies
– Surveys
– Routine monitoring
– Interpretation of result
– Basic statistical analysis
– Quality assurance
Sampling Strategies
• Primary Objective:
– Provide analytical information about the workplace
• Other objectives:
– Investigate complaints
– Compliance to exposure limits
– Evaluate effectiveness of controls
Sampling Strategies (cont)
• Cannot formulate a sampling strategy until the
objectives of the exercise are clear & understood
• Need to ask the question:
“How will the data generated from this exercise be used?”
Sampling Strategies (cont)
• BOHS suggests consideration of the following before
developing any monitoring programme
– Qualitative risk assessment
– Measurements other than airborne samples (bulk
samples, airflow patterns)
– Biological monitoring
– Other health hazards
– Any environmental or worker characteristics
Factors to Consider in a Monitoring Strategy
• Type of samples (area v personal)
• Location of sampling device (area)
• How many samples
• Length of sampling interval
• What period of the day should monitoring occur
so as to be consistent with work patterns
Factors to Consider in a Monitoring Strategy (cont)
• How should the samples be taken
• Contaminants likely to be present
• What are the expected concentrations
• Potential interferences with sampling or analytical
method
• Analytical method and possible constraints
Surveys
• Initial appraisal
• Basic survey
• Detailed survey
• Routine survey
Initial Appraisal
• Commonly called a “walkthrough survey”
• Can provide answers to these questions:
– What are the potential exposures
– Where & when do they occur
– Can exposures be prioritised in terms of risk
– Is further evaluation necessary
– If so, what is the preferred approach
Initial Appraisal (cont)
• While the “walkthrough survey “ gives basic
information you may still need further information on:
– Physical properties of substances
– Physical form in the workplace
– Potential routes of intake
– Any skin effects
– Any available exposure limits
Basic Survey
• Generally required when:
– Initial appraisal indicates unacceptable exposures
possible
– New process being commenced
– Substantial changes to a process, operations or
control measures
– Unusual events (e.g. maintenance)
– New exposure limit declared
Basic Survey (cont)
• Possible objectives:
– Confirmation (or otherwise) of possible
unacceptable exposures from initial appraisal
– Information on engineering or other controls
– To establish if a more detailed survey is necessary
Basic Survey (cont)
• Questions to be addressed before proceeding:
– Who should be monitored ?
– When should they be monitored ?
– Where should the monitoring occur ?
– How should the sampling occur ?
Basic Survey (cont)
• Other factors
– Legislative requirements
– Accuracy & precision required
– Intrinsic safety requirements
– Laboratory analysis
– Transport of samples
– Portability of equipment
Detailed Survey
• Usually has a clear objective
– to obtain reliable measurements, reach
conclusions regarding exposure & decide control
measures
• Results need to be representative of personal
exposures & appropriate method used to compare
results to exposure standard
Detailed Survey (cont)
• All aspects of survey need to be reviewed to
minimise errors
– statistical based monitoring & analysis sometimes
used
Routine Surveys
• Generally involve periodic sampling to meet defined
goals, such as:
– Checking control measures
– Compliance
– Corporate requirements
– Epidemiological studies
Routine Monitoring
• Issues that need to be considered:
– Frequency
– Sampling methodology
– Number of samples required
– Type of data analysis
Frequency of Routine Surveys
• No set rules but the following should be considered
when making judgments:
– How close are exposures to exposure standard
– How effective are the controls
– What is the process cycle
– Seasonal & shift variation
– High variability in data
Statistical Based Monitoring
• Approach developed in 1970’s by NIOSH
• Collect a statistical sub-set of worker exposure to
represent all persons’ exposure in a Similar Exposure
Group (SEG)
• Sampling must be random
• Number of samples collected determined by required
confidence level
Process of Statistical Monitoring
• Establish similar exposure groups (SEGs)
• Develop statistically based sampling schedule
• Collect data
• Statistically analyse data
Process of Statistical Monitoring (cont)
• Modify exposure groups (if required)
• Final report
• Ongoing data collection (maintenance sampling)
Establish Similar Exposure Groups
• Can be defined :
– By process and environmental agent
– By process, job and environmental agent
– By process, job, task and environmental agent
– By process, task and environmental agent
– By work teams
– By non-repetitive work
Establish Similar Exposure Groups
• Observational
– Simplest form but least accurate
• Sampling
– Preliminary sampling to establish groups
• Combination of observation and sampling
– Most accurate approach
Interpretation of Results
• Compliance analysis
– Legislative requirements
• Non compliance analysis
– Solely end use dependent
– Project outcomes drive how the data is evaluated
Basic Statistical Analysis
• Distribution of data
• Basic statistical formulae
• Other statistical measures
• Log probability plots
Normal v Lognormal Distributions
Source: AIHA 1998 – reproduced with permission
Occupational Hygiene Data
• The lognormal distribution generally best fits
occupational hygiene data (but not always)
• One reason is you cannot have exposures with a
concentration less than zero & potentially there is no
upper limit to exposure levels
Basic Statistical Formulae
• Arithmetic mean – AM
• Standard deviation – SD or s
• Geometric mean – GM
• Geometric standard deviation - GSD
Basic Statistical Formulae (cont)
AM
=
∑Xi
n
SD(s)
= v
_
 (Xi – X)2
n-1
Where  = sum of individual exposures of X and n is the number
of observations
Basic Statistical Formulae (cont)
 (ℓnX)
GM
= e
n
_
 (yi – y)2
GSD
= e v
n-1
Where y = ℓnX and n = number of observations
How GSD Can Be Useful?
GSD
1.0
<1.44
1.5-2.0
2.0-3.5
>3.5
Inference
No variability. All readings have same value
Data approximates a normal distribution
Very little variability in data
Moderate variability in data
High variability in data
Other Statistical Measures
• Upper & lower confidence limits
• 95th percentile
• Minimum Variance Unbiased Estimate (MVUE)
Confidence Limits - (Lands)
• Provides an estimate of the error of the AM (or MVUE)
for a lognormal dataset
Sy
CL = exp In (û) + C  n-1
{
}
Where Sy = SD of log transformed data
C = Land’s C factor
n = number of data samples
û = exp ( y + ½ Sy2 )
y = mean of the dataset
Why is 95% Confidence Generally Used?
• Convention
• Arbitrary decision - Ronald A Fisher in 1926
• First used in a paper by Fisher describing how to
assess whether adding manure to a field would
increase crop yields
• Not a rigid criterion for “truth”
95th Percentile
• Useful when evaluating the health hazards of agents
with acute effects
• Used by some corporations as a measure of
compliance
MVUE
• Minimum Variance Unbiased Estimate (MVUE) : The
estimate of the true mean of a lognormal dataset
MVUE =
GM v MVUE (AM)
Source: AIHA 1998 – Reproduced with permission
Log Probability Plots
• Gives visual assessment of distribution
• Can highlight mixed SEGs
• Can obtain other statistical data from graph
– eg GM (50%ile) and GSD (84%ile/50%ile)
• Need to plot concentration against r/(n+1) where
r = rank and n = number of results on logprobability paper (lognormal distribution)
Computer Generated Log Probability Plot
Logprobability Plot and
Least-Squares Best-Fit Line
99%
98%
95%
90%
84%
75%
50%
25%
16%
10%
5%
2%
1%
0
1
Concentration
10
Source; University of Wollongong
Quality Assurance
• Confidence in workplace exposure data requires:
– An appropriately validated method
• Numerous quality assurance schemes throughout the
world to check methods & laboratories
– Appropriate sampling methodology & practice
• No current schemes
• Need to self audit
Air Sampling Theory & Practice
• Survey design
– Non sampling approaches
– Sampling numbers
– Sampling patterns
– Sampling to assess acute or chronic effects
– Practicalities of sampling programmes
Non Sampling Approaches
• Control banding
– Developed in the late 1980’s by the pharmaceutical
industry
– Compounds classified into bands by their toxicity
– Each band aligned with a control scheme
Control Bands – Example ( Chemicals by Inhalation)
• Band 1 – Use good industrial hygiene practice &
general ventilation
• Band 2 – Use local exhaust ventilation
• Band 3 – Enclose the process
• Band 4 – Seek expert help
Systems Currently in Place or Under Development
• HSE (UK) COSHH Essentials
• ILO Chemical Control Tool kit
• Systems currently being developed in:
– Belgium (REGETOX)
– Netherlands (Stoffenmanager)
– Norway (KjemiRisk)
Limitations of Non Sampling Approaches
• Do not work in all situations
– “hot” processes
– Open spray applications
– Gases
• Provide general guidance for the “most likely”
scenario however industry & task specific guidance
is becoming increasingly available
• Do not take account of individual process variations
Sample Numbers
• Fundamental question always asked – how many
samples do I need to provide representative & useful
information?
• Depends on information required:
– Compliance
– Epidemiology
– Corporate requirements
– Degree of confidence
Number of Samples – Some Methods
• General rule of thumb : 1 in 10 workers with minimum
of 3 and spread of results < 25%
• Using rough estimates of the mean & standard
deviation
– Number = (tvalue.CV/E)2
Where: CV = Coefficient of variation (rough SD/rough mean)
E = Error you are prepared to accept
tv = t-Statistic for degrees of freedom
(number of measurements in preliminary survey – 1)
Rough Estimates Approach (Example)
• Took 5 measurements with rough mean of 60ppm and
a SD of 15ppm
• CV=15/60=0.25
• Degrees of freedom=5-1=4
• T-statistic (95% confidence) = 2.776 (from tables)
• Error that is acceptable=15% (or 0.15)
• Number of samples=(2.775x0.25/0.15)2
= 4.622 or about 22
Number of Samples – Some Methods (cont)
• Rappaport & Selvin (1987)
– Determines the number of samples needed to test
the mean exposure of a lognormal distribution of
exposures against the exposure standard
– Requires some preliminary data
Rappaport & Selvin (α=0.05,β=0.10)
Rappaport & Selvin (Example)
If F = 2 & GSD =2 then number of samples = 6
If F = 0.75 & GSD = 3 then number of samples = 266
( there is a 5% chance that it is claimed that workplace
complies with ES when in fact it does not. 10% it
would not be claimed to comply when in fact it did)
NIOSH Compliance Method
The Real World
• Extensive sampling - significant cost
• Statutory compliance may not be the aim of the
sampling project
• Resources are usually limited
Practical Options
• Point of diminishing returns
• Reasonable approximation of exposure profile
possible with about 6-10 samples (AIHA 1998 & 2006)
• As exposure approaches exposure limit this number
increases depending on level of confidence required
Point of Diminishing Returns
Source : AIHA 1998 –
Reproduced with permission
Sampling Patterns
• Grab samples
• Partial period consecutive samples
• Full period consecutive samples
• Full period single samples
Sampling Patterns
Source: NIOSH 1977
Exposure Profile in Real Time
Concentration
Time
Sampling to Assess Acute or Chronic Effects
• Toxicology of substances can influence design of
sampling strategies
• Need to sample over an extended period for chronic
acting substance & over a shorter period for acute
acting substances (or both for some substances)
Sampling to Assess Acute or Chronic Effects (cont)
Example of toxicological properties v sampling strategy
• Quartz- chronic acting substance hence need to
sample over extended period e.g. full shift (TWA)
• Ammonia - fast acting substance hence sampling
is conducted over shorter period e.g. 15 minutes
(STEL)
Practicalities of Sampling Programmes
• Large statically based monitoring programmes are
very expensive & rare outside major corporations
• What can one person reasonably do in a sampling
exercise
– Difficult to calibrate, distribute, monitor & recalibrate more
than 5 sampling devices
– Need to ensure the quality of data, the persons & situations
sampled be appropriate & be able to explain abnormalities
in data
Practicalities of Sampling Programmes
• Relationship between observations & measurements
is critical
– Better to have fewer samples that can be interpreted rather
than large numbers of samples which can’t
• The process may limit the sampling approach
– Batch processes for example do not lend themselves well
to statistically based random sampling exercises
Air Sampling Theory & Practice
Personal Sampling
• Breathing zone
• Operator variability
Personal Sampling (cont)
• Inhalation is main route of entry to the body
– Estimate of exposure should be conducted in a location
consistent with inhalation patterns
• Breathing zone
– Personal samples
– The shape of the head can result in significant
concentration differences over short distances
Breathing Zone
300mm Hemisphere
around the nose and
mouth
Personal samples
MUST be taken in the
Breathing Zone
Source :Airmet Scientific – reproduced with permission
Operator Variability
• Exposure pattern & concentrations are in a state of
constant flux due to:
– Changes in the process
– Changes in ventilation rates
– Changes in climatic conditions
– Range of workers tasks within a day
– Individual worker practices
Air Sampling Theory & Practice
• Area sampling
– General or background measurements
– Particle size
– Breathing air quality (air supplied respirators)
General or Background Measurements
• Commonly referred to as static or area samples as
they are not collected on a person but in a fixed
position
• Do not correlate well with actual personal exposures
but useful for:
General or Background Measurements (cont)
• Checking control devices
• Identifying contaminant sources
• Identifying potentially unacceptable areas of
exposure
• Continuous monitoring
• Sampling high volumes (e.g. asbestos clearance)
Particle Size
• Distribution of an aerosol in an air stream depends
on its aerodynamic properties
• Aerodynamic diameter key factor of particles in
settling rates
• Particle size can influence contaminant concentration
– Mixed dust may have one particular contaminant
concentrated in one particular size range
Breathing Air Quality
• Quality of air generated by compressors for air
supplied or self-contained breathing apparatus
should be checked at regular intervals
• Common contaminants are oil mist & carbon
monoxide however corroded pipe work &
condensation can give rise to an astringent taste
• Most systems have inline filters but these have a
finite life and must be checked regularly
Air Sampling Theory & Practice
• Surface & other measurements
– Surface contamination measurements
– In-situ XRF metal analysis
– Bulk sampling
– Skin exposure
Surface Contamination Measurements
• In any comprehensive risk assessment for exposure
to contaminants it is important to consider
contributions from all areas e.g. surfaces
• Depends to a large degree on toxicology
– Common in nuclear industry
Methods for Evaluating Surface Contamination
•
•
•
•
•
•
Micro vacuuming
Disposable paper towels
Manual wipe methods
Adhesive tape
Colourimetric pads (acids & alkalis)
Specific instrumentation
– Mercury “sniffers”
In – situ XRF Metal Analysis
• Small hand held XRF analysers are useful field
instruments
– Metal analysis of coatings etc
– Contaminants in soils & bulk materials
• Particle size & surface preparation can influence
results
– Improved analysis when sample dried, sieved, ground or
pressed
Bulk Sampling
• Used to identify contaminants in the workplace
– Especially useful in old buildings or sites
– Collect samples from places where dust etc is
likely to collect
• Used for asbestos identification
• Usually analysed by a laboratory
Skin Exposure
• Dermal exposure can be a significant contribution to
exposure for some contaminants
• Especially the case with pesticides but other
compounds can be absorbed this way
Methods of Dermal Evaluation
• Direct
– Dermal dosimeters in the form of patches
– Skin washes & wipes
– Video detection of fluorescent tracers
• Indirect
– Measurement of some biologic response such as
cholinesterase activity for exposure to pesticides
RISKOFDERM
• European developed model & risk assessment toolkit
• Toolkit constructed by analysing the major
determinants of dermal hazard & control
• Results combined into a decision “tree”
RISKOFDERM (cont)
• User responses to questions are translated into
hazard & exposure categories – outcomes are
estimate of health risk & suggested control strategies
• Hazard categories
– Local & systemic effects
– Uptake through the skin
RISKOFDERM (cont)
• Exposure categories
–
–
–
–
–
–
Handling contaminated objects
Manual dispersion
Hand tool dispersion
Spray dispersion
Immersion
Mechanical treatment
• Considerable criticism of model has occurred
Confined Spaces
Confined Spaces
• Identification & nature of hazards
• Monitoring in confined spaces
• Case study 2
Identification & Nature of Hazards
• Hazardous substances
• Flammable atmospheres
• Unsafe oxygen levels
• Engulfment
• Physical & other factors
– Manual handling, noise, radiation etc
Monitoring in Confined Spaces
• Never trust the human senses
• Risk assessment should identify requirements for
monitoring
• General approach is to test for:
– Oxygen content
– Flammable compounds
– Harmful contaminants / “toxics”
Monitoring in Confined Spaces (cont)
• Intrinsically safe monitoring equipment is usually
required
• Telescopic probes can be useful
• Need to understand properties of potential
contaminants
– Are they heavier than air
– Are they lighter than air
• Need to monitor immediately prior to entry
Monitoring in Confined Spaces (cont)
• Re-testing & continuous monitoring required:
– If determined by risk assessment
– If indicated by initial testing of atmosphere
– Because of potential for later release of
contaminants
– Because of work in confined space – e.g. welding
Case Study 2
Rice-growers Co-operative Limited
Double Fatality
The Site
Source; J Henderson – reproduced with permission
The Rice Shed
Source; J Henderson – reproduced with permission
The Elevator Pit
Source; J Henderson – reproduced with permission
Initial On Site Analysis
Combustible gases
Carbon dioxide
Not Detected (ND)
0.06 %
ES 0.5%
IDLH 5 %
Carbon monoxide
ND
ES 25 ppm
IDLH 1500 ppm
Hydrogen sulphide
15 ppm
ES 10 ppm
IDLH 300 ppm
ES
Exposure Standard
IDLH Immediately Dangerous to Life & Health
Gas Bag Analysis
Normal Atmospheric Gases
Oxygen
Carbon dioxide
Nitrogen
Asphyxiants
Methane
Ethane
Propane
Contaminant Gases
Carbon monoxide
Hydrogen sulphide
20.7 %
Trace
79.2 %
(20.9%)
(0.04%)
(78 %)
Trace
ND
ND
ND
Trace
(ES 25 ppm)
(ES 10 ppm)
Head Space Gas Analysis
Hydrogen sulphide
Wine flagon
Soft drink bottle
540 ppm
450 ppm
ES
IDLH
10 ppm
300 ppm
Microbiological / Water analysis
Pit Brew Water
9000 H2S producers/ml
Bore (seepage) water 1000 - 4000
”
Hydrogen sulphide (eg clostridium) formers reduce
sulphur compounds to sulphides causing a
blackening of the colonies as exhibited by
the water in the pit.
Hydrogen Sulphide – Health Effects
ppm
Effect
0.1 - 30
Odour of rotten eggs - obvious &
unpleasant
50-100
Marked dryness & irritation of nose &
throat
100-150
Temporary loss of smell - olfactory
fatigue
Hydrogen Sulphide – Health Effects (cont)
ppm
Effect
200-250
Severe irritation, headache, nausea exposure for 4 hours can cause death
500+
Rapidly unconscious & respiratory
failure in 5 mins
1000 +
May cause coma after a single breath &
rapidly fatal
Hypothesis
- Hydrogen sulphide from anaerobic bacteria action
in pits & released by violent agitation
- NOT Carbon monoxide from combustion engine
- Plan to simulate events
Simulation of Events
Prior to agitation
Oxygen
Carbon monoxide
Carbon dioxide
Combustible gases
Hydrogen sulphide
20.8 %
ND
0.06 %
ND
ND
Simulation of Events (cont)
Agitation of the pit by malfunctioning pump
Oxygen
Carbon monoxide
Carbon dioxide
Combustible gases
Hydrogen sulphide
20.8 %
ND
0.06 %
ND
300 ppm
Hydrogen Sulphide Incidents
• Similar hydrogen sulphide incidents have been
reported in the following industries
– Meat processing
– Chicken processing
– Leather processing
Case Study 3
Case Study 3 – Process Review & Survey Design
• Break up into groups
• Review the process – gold extraction plant
• Using the student manual & presentation notes :
– Provide an initial appraisal of the workplace
– Design a basic survey
– Design a detailed survey
– Suggest a routine monitoring programme
Case Study 3 (cont)
• Prepare a 5 minute presentation
• Time for exercise is 60 minutes
• Ask the lecturer for guidance if unsure of how to
proceed
• Put yourself in the position of a hygienist asked to
assess this situation – what would you do?
Case Study 3 – Transport of Crushed Ore
Source: B Davies – Reproduced with permission
Case Study 3 – Adding Chemicals
Source: B Davies – Reproduced with permission
Case Study 3 – Gold Room
Source: B Davies – Reproduced with permission
BIOLOGICAL MONITORING
Definition
Biological exposure monitoring, or
biological testing, is a way in which you can
determine how much of a particular
contaminant has entered and has been
taken up by the body
Biological Monitoring
• Provides additional information where there is a
respiratory hazard
• Can be used where main exposure route is NOT
inhalation
Biological Monitoring (cont)
• Can highlight deficiencies in:
– the wearing of PPE ie respirators, gloves or
protective clothing
– poor work practices
– poor personal hygiene
• Provides evidence for medical assessment
Biological Monitoring (cont)
1. Direct biological monitoring or biological monitoring
of exposure, or
2. Biological effect monitoring
Direct Biological Monitoring
Of the specimen:
•
•
•
•
Blood e.g. for lead, mercury
Urine e.g. for cadmium and MOCA
Hair and nails e.g. for arsenic
Breast milk & body fats e.g. for pesticides
and PCBs
• Expired air e.g. for carbon monoxide and
organic solvents eg alcohol, benzene
Direct Biological Monitoring (cont)
Analysis of its metabolites
Blood e.g. carboxyhaemoglobin from carbon
monoxide
Urine e.g. mandelic acid from styrene
Biological Effect Monitoring
Aimed at identifying early & reversible biochemical
changes resulting from exposure e.g.
- zinc protoporphyrin in blood – increase with
exposure to lead – inhibits biosynthesis of heme
- cholinesterase activity in red blood cells –
exposure to organophosphate pesticides
depresses cholinesterase activities
What Has To Be Considered?
Extent & rate absorption
Properties of chemical
Solubility in lipids & water
Route of exposure
Once absorbed
Where distributed to
Susceptibility of tissues – pH, permeability
Water soluble - may be in total body water
Non polar - may be in the body fat
What Has To Be Considered? (cont)
Elimination depends on:
Metabolism
oxidation, reduction, hydrolysis or
combinations
Excretion routes
faecal, urinary, exhalation, perspiration &
lactation
May be excreted without metabolism
CHOICE OF INDICATOR & TIMING IS CRITICAL
Biological Half-Life
• Is the time required for half of a substance to be
removed from the body by either a physical or
chemical process
• Half lives vary significantly for different substances
and hence the importance of sample collection times
–
–
–
–
–
Lead in bones
T1/2 = 20 years
Lead in blood
T1/2 = 35 - 40 days
Arsenic in urine
T1/2 = 1 - 2 days
Mercury in urine
T1/2 = 40 days
Mercury in brain several years
Sampling & Collection Times
Recommended collection or sampling time must be
observed & recorded
ACGIH BEI® suggest :
Sampling time
Recommended collection
Prior to shift
16 hrs after exposure
During shift
Anytime after 2 hrs of exposure
End of shift
As soon as possible after exposure ceases
End of work
week
After 4 or 5 consecutive work days with exposure
Discretionary
At any time
Sampling / Collection Times (cont)
UK HSE Guidance Note EH56 suggests:
Half life
< 2 hours
Optimum Time for Taking Samples
Conc. changes too fast – not suitable
2 to 10 hours
End of shift or next morning
10 to 100 hours End of shift at end of week
> 100 hours
Random sampling acceptable
Urine Specimen Acceptability
Concentration of urine has marked effect on results
WHO guidelines - highly diluted or concentrated
samples:
Creatinine concentration > 0.3 g/L and < 3 g/L
OR
Specific Gravity
> 1.010 and < 1.030
If outside limits discard and resample
Some of the Common Industry Exposures
Petroleum
– PAHs – 1 hyroxypyrene in urine
– Benzene – S-phenylmercapturic acid in urine
t,t-muconic acid in urine
– Lead – in blood
Some of the Common Industry Exposures (cont)
Plastics
– BTX – mixture of benzene, toluene & xylene
– Solvents
Acetone in urine
Ethyl benzene
• mandelic acid in urine
• ethyl benzene in expired air
Phenol – total in urine
Some of the Common Industry Exposures (cont)
Pesticide
– Organophosphates: cholinesterase activity in red
blood cells
Spray painting
– Solvents
– Isocyanates
Aluminium
– Fluorides in urine
Biological Exposure Indices - BEIs®
• BEIs® are guidance values for assessing biological
monitoring results
• Represent the levels of determinants that are most
likely observed in specimens collected from workers
who have been exposed to chemicals to the same
extent as workers via inhalation exposure at the TLV ®
Biological Exposure Indices - BEIs®
ACGIH BEIs®
Handbook & Documentation
Results compared against BEIs® list (approx 40)
Guidelines in evaluation of health hazards
Apply to 8-hour exposures, 5 days a week
BEI® Committee does NOT recommend time
correction factors
BEIs® Notations
B = Background
– Determinant may be present from subjects who
may not have been occupationally exposed
Nq = Nonquantitative
– Biological monitoring should be considered – but
a specific BEI® for this substance could not be
determined due to insufficient data
BEIs® Notations (cont)
Ns = Nonspecific
– Determinant non specific, also observed after
exposure to other chemicals
Sq = Semi-quantitative
– Determinant is an indicator of exposure, used as a
screening test
Application of BEIs®
• Guidelines only
– Not fine distinction between hazardous & non
hazardous exposures
• Variable nature of concentrations in specimens
– Don’t rely on 1 result
Application of BEIs® (cont)
• Apply to 8-hr, 5 day week – use list as is
• Values inappropriate for general public and non
occupational exposures
• Should only be used by knowledgeable professionals
UK Limits
HSE established non statutory Biological Monitoring
Guidance Values (BMGVs)
Based on biological concentrations & health effects or
biological concentrations & exposure at WEL
HSE Website www.hse.gov.uk
EH 40/2005 Workplace exposure limits
Confidentiality
Ethical & confidentiality issues:
•
•
•
•
•
Method appropriate for requirements of investigation
Procedures should not threaten health of participant
Risk of invasive methods be justified by the benefits
Informed consent from the participants needed
Results kept confidential between occupational
health professional & participant
Sample Analysis
Sample Analysis
• Field samples sent to the lab for analysis
• Need to enure correct (validated) techniques are
used
• Need to consult with laboratory
Talk to the Laboratory!!
• Select an appropriate monitoring and analytical
method
• Talk with the analytical laboratory
• Understand the principles of direct reading
instruments
• Make an assessment of the analytical results
BEFORE SAMPLING TALK TO THE LABORATORY
Analytical Techniques
• Spectroscopy
• Chromatography
• X-Ray diffraction / fluorescence
• Mass Spectroscopy
• Gravimetric
• Microscopy
Spectroscopy
Basic principle
• All elements absorb or emit electromagnetic radiation
ie light at a specific frequencies or wavelengths
• The amount of energy absorbed or emitted at a
particular frequency for that element is proportional
to its concentration
Atomic Spectroscopy
Typically for analysis of metals (approx. 60)
Dusts & fumes collected on filters
Metallic vapours eg mercury, arsine into impingers or
adsorption onto a solid
– Flame Atomic Absorption Spectrometry (AAS)
Schematic of AAS Principle
Source: BP International
Atomic Absorption Spectrometer
Source; University of Wollongong
Atomic Spectroscopy (cont)
– Hydride Generation
Arsenic and selenium poor sensitivity with AAS (far UV)
Converted to hydrides AsH3 & H2Se
Swept through flame or heated quartz cell with increased
sensitivity
Flameless Atomic Absorption
AAS not sensitive enough for low concentrations of
metals in biological samples eg blood
– Graphite furnace
Sample in hollow graphite tube rapidly heated with high
electric current to atomise sample
– Cold vapour generation – Mercury (Hg)
Hg volatile at room temperature. Hg compounds
reduced to metallic Hg and transported to cell by stream of
gas
Atomic Emission Spectrometry
Flame excitation of element, but is looking at
emission of energy when returning to ground state
– Flame emission
AES can be operated in emission mode or a flame
photometer can be used.
Typically used for alkalai and some alkaline earths
eg sodium and potassium
Graphite Furnace AAS
Source; University of Wollongong
Atomic Emission Spectrometry (cont)
– Inductively Coupled Plasma Spectrometry (ICP)
Extension atomic emission spectrometry
Gas plasma temps to 10,000°C – increased numbers of
excited atoms hence increased sensitivity.
Elements (approx 60) can be analysed
simultaneously
Metals, silicon and carbon
Inductively Coupled Plasma Spectromer (ICP)
Source; University of Wollongong
Molecular Spectrophotometry
– UV-Visible Spectrophotometry
• Metals or organics
• Collected onto filters or by impinger
• Principle absorption of UV & Visible light by excitation of
the bonding molecules
Schematic of a Single Beam UV-VIS
Source: BP International
Molecular Spectrophotometry (cont)
– UV-Visible Spectrophotometry
• Most chemical species absorb UV or Visible
radiation & can therefore be quantified
•
For those that don’t absorb a colour producing
agent can be added and then the the colour
intensity can be measured e.g. Cr6+ using
diphenyl carbazide
Infra-red (IR) Spectrophotometry
Each molecular species has its own unique absorption
spectrum or “fingerprint”. Absorption or emission of IR
results in a change in vibration or rotation of a molecule.
Typically used for organics & covalently bonded
metal complexes & quartz
IR Spectrum for Quartz
Source; University of Wollongong
Molecular Fluorescence
Fluorescence is one way a molecule returns to its
ground state after excitation.
Emission of radiation at characteristic wavelengths
different from the exciting wavelengths
Used for aromatic hydrocarbons including oils
Chromatography
Is a separating method typically used for analysis of organics.
Packed column hold the stationary phase as mobile phase
carries the sample as it separates out through the column.
Detectors - flame ionisation, mass spectrometer, thermal
conductivity, electron capture
Gas Chromatograph
Source; University of Wollongong
Gas Chromatograph Mass Spectrometer
Source; University of Wollongong
Other Analytical Techniques
– X-Ray Diffraction
Identify & quantify crystalline substances
Direct on filter e.g. silica analysis – different forms have
different health effects
– Quartz SiO2 – TLV 0.1 mg/m3 (respirable)
– Kaolin Al2SiO5(OH4) – TLV 10 mg/m3 (inhalable)
– Amorphous silica – TLV – 10 mg/m3
Other Analytical Techniques (cont)
– X-Ray Fluorescence
Identification of elements
Multi-channel instruments up to 24 elements
Ashes, ores, minerals, alloys & metals
Mass Spectroscopy
– Sample converted to gaseous ions & separation
on the basis of charge to mass ratios
– Provides qualitative and quantitative information
– Identification of unknowns
Detection Limits - Example
Sampling rate 2 L/min
Limit of Detection 10 µg
If the TLV is 0.1 mg/m3
Minimum sampling time = 10 x analytical limit of detection
Exp standard x flow rate
= 10 x 10 µg
= 100 µg/m3 x 2 x 10-3 m3/min
= 500 mins
ie full shift sample required
Sources of Analytical Methods
• NIOSH Manual of Analytical Methods (NMAM)
– Over 1,700 methods in air & blood
– On line
• UK HSE MDHS Series
– More than 100
– On line
• OSHA Standard Methods for sampling
– On line
Sources of Analytical Methods (cont)
• ISO – Standard Methods for Sampling & Analysis
• National Standards in many countries
• SKC Inc Comprehensive Catalog & Sampling Guide
– Over 2,500 specific compounds – on line
Filters
Particles trapped / caught on filter media by:
– Interception
– Impaction
– Diffusion
Filters (cont)
Media requirements:
– High collection efficiency
– Manageable resistance
– Low moisture pick up or loss
– Low electrostatic properties
– Compatible with analytical technique
– Low cost
Filters (cont)
Filter types:
– Mixed cellulose ester
– PVC
– Teflon
– Polycarbonate
– Silver
– Glass fibre
– Quartz
– Cellulose
Filters (cont)
• Pore size
– Nominal pore size – not a sieve
– Tortuous path – increase collection efficiencies
– Exception polycarbonate
• Treated / impregnated filters
– Particulate and gaseous contaminant
– Glutaraldehyde – Glass Fibre/2,4dinitrophenylhydrazine
– Fluorides – Teflon/sodium carbonate
Filters (cont)
• Moisture loss and pick up
– Equilibration and field blanks
• Electrostatic charge
– Static eliminator (Zerostat Gun)
– Radioactive source
Zerostat Gun
Source; University of Wollongong
Laboratory balances
• Microbalance
– Sub milligram quantities
– Regular calibration
• Filter & sample head preparation and unloading
– Need for caution or material can be lost
Laboratory balances (cont)
Accuracy via:
– Repeatability test every 6 months
– Before every weighing session : check with
reference weight
– During every weighing session : zero check
– After every weighing session: check with reference
weight
– Long weighing sessions : check at appropriate
intervals
Polarized Light Microscopy
Used for counting fibres- particles with thread like
appearance with specific length to width ratio:
– Asbestos, fibreglass, rockwool & ceramic fibres
– Standard methods for monitoring and counting of
asbestos & other fibres
Asbestos Counting
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Gridded filter (MCE)
Collapsed/cleared with acetone & glyceryl triacetate
Phase contrast light microscopy
Kohler illumination
Walton & Becket graticule
Counting rules
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Length to breadth ratio
No. of fields
No. of fibres
Fibres / ml
Source: A Rogers-reproduced with permission
Dispersion Staining
Used for fibre identification
– Suspension of fibres in liquids of known refractive indices
– Observe colours displayed under polarised light in different
axis
Chrysotile
Amosite 1st Order Red Retardation
Source: A Rogers-reproduced with permission
Quality Assurance of Analysis
Internal quality control
• Method validation (use of validated methods)
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Check for accuracy – adding known amounts
Check for precision – analyse replicate samples
Measurement range
Interferences
Capacity of collection media
Sample stability
Critical steps in the analytical process
Quality Assurance of Analysis (cont)
• Standards
– Standard reagents of known purity & composition
– Calibration standards, calibration curves
• Blanks
– Field blanks should be submitted with field samples
– Checks for contamination
– Laboratory reagent blanks
• Control Materials
– Previously analysed and run against field samples to
compare actual with expected result
Quality Assurance of Analysis (cont)
• Recoveries
– Part of validation, but should be ongoing
• Duplicates
– From the field more useful for assessing sampling or
analysis rather than duplicate analysis ie repeat injections
into the GC from one “bottle”
• Quality control charts
– Provide a means of showing reliability of each method
– Identifies trends or cyclical changes
External Quality Control
Quality Control Schemes (Proficiency schemes)
• NIOSH – Proficiency of Analytical Testing (PAT)
– Solvents on charcoal; asbestos, silica & metals on filters
• UK HSE – Workplace Analysis Scheme for
Proficiency (WASP)
– Solvents on charcoal, metals on filters
Quality Assurance of Analysis (cont)
Laboratory Accreditation
National schemes:
• AIHA program in USA
• UKAS in UK
• NATA in Australia
Quality Assurance of Analysis (cont)
Typically assessed for:
– Qualifications & experience of staff
– Calibration & maintenance of instruments
– Accommodation
– Laboratory practice
• Sample handling
• Quality control
• Recording & reporting
• Test methods used
Review of Today’s Learning Outcomes
• Receive guidance in understanding the reasons for
any incorrect answers to the overnight questions
from Day 1
• Understand the principles of sampling for airborne
contaminants and be able to use those principles to
devise a suitable sampling strategy
Review of Today’s Learning Outcomes (cont)
• Be familiar with the requirements for monitoring in
confined spaces and understand some of the issues
that need to be considered during this process
• Understand the principles of biological monitoring
and their appropriate application
Review of Today’s Learning Outcomes (cont)
• Be familiar with the various methods that are used to
analyse the various contaminants found in the
workplace
• Understand the requirements to ensure the quality of
laboratory analysis