# Study_Guide-Exposure_Assessment_Air_Sampling_2015

```Exposure Assessment and Air Sampling
Study Guide for CIH Immersion Presentation
C.R. Manning, F.T. Posey, Mary Eide
1
Part 1 - Exposure Assessment
Exposure Assessment - Figuring out what to monitor and how often to monitor
•
What Chemicals Are Present?
–
Facility Documents
•
Chemical Inventory
•
Operating Procedures
•
Material Safety Data Sheets
–
Walk-Around Survey
–
Interview Workers
–
Interview Medical & Safety Staff
Identify Exposure Limits
•
Occupational Exposure Limits (OELs)
–
OSHA PEL
–
ACGIH TLV
–
NIOSH REL
–
In House OEL
2
3
Health Effects Priority
Health Effects Ratings
4 = Life Threatening
3 = Irreversible Health Effects
2 = Severe, Reversible Health Effects
1 = Reversible Health Effects
Exposure Ratings
4 = Exceeds OEL (PEL)
3 = 50-100% of OEL
2 = 10-50% of OEL
1 = < 10% of OEL
Health Effects Priority Scoring
•
•
Agent A
–
Health Effects Rating = 3 (Irreversible Health Effects)
–
Exposure Rating = 3 (50-100% of OEL)
–
Exposure Assessment Priority … 3 x 3 = 9
Agent B
–
Health Effects Rating = 2 (Reversible Health Effects)
–
Exposure Rating = 2 (10-50% of OEL)
–
Exposure Assessment Priority … 2 x 2 = 4
4
5
Modeling A
•
50 gm of Agent A (molecular wt = 111) is used daily in a Room that is 40ft long,
40ft wide, and 20ft high.
•
If every bit of Agent A evaporated and stayed in the room, what would the worstcase concentration be?
–
(40ft x0.30 M/ft)(40ft x 0.30M/ft)(20ft x 0.30M/ft) = 864 M3
–
(50gm x 1000 mg/gm) / 864 M3 = 58 mg/M3
What would the Concentration be in in parts per million (ppm)?
(58 mg/M3) x (24.45 L/mole)
=
13 uL/L = 13 ppm
(111 g/mole)
Modeling B
•
50 gm of Agent A (molecular wt = 111) is brought into in a Room that is 40ft long,
40ft wide, and 20ft high.
•
At the end of the work shift, 20 gm of Agent A is left over.
•
Assume the missing quantity of Agent A evaporated, and the Room ventilation
provides 10 air changes per work shift.
•
Now what would the worst-case concentration of Agent A be?
–
(40ft x0.30 M/ft)(40ft x 0.30M/ft)(20ft x 0.30M/ft) = 864 M3
–
(30gm x 1000 mg/gm) / (10) (864 M3) = 3.5 mg/M3
What would the Concentration be in in parts per million (ppm)?
(3.5 mg/M3) x (24.45 L/mole) = 0.76 uL/L = 0.76 ppm
(111 g/mole)
6
Similar Exposure Group (SEG)
•
If there are many workers to monitor, it is useful to divide workers into groups
believed to have Similar Exposures.
•
Criteria for SEGs
•
–
Same facility; Same job; Similar process
–
Historical monitoring results are similar
–
Verify SEGs through Monitoring experience
Each monitoring, sample a fraction of workers in SEG
–
•
25%, 20%, 10% (eventually you will sample everybody)
Analyze Sampling Results & Control SEG as a group
–
Continue to verify that SEG members belong together
Limitations of Models
•
Modeling works well when Models are simple and results are clear-cut.
•
Enables the IH to avoid wasting resources monitoring situations with minimal
risk.
•
When simple models do not produce clear-cut results … you will need to Monitor.
7
Part 2 – Air Sampling for Vapors
Sources of Workplace Air Sampling Methods
1. OSHA Methods (web-site: www.osha.gov )
2. NIOSH Methods (NMAM) (web-site: www.cdc.gov/niosh )
3. EPA Methods (website: www.epa.gov )
5. Media Manufacturer Sampling Guide
Direct Reading Instruments – assessing the situation
1. Colorimetric Detector tubes – color on tube compared with indicator ruler
a. Colorimetric or detector tubes and passive samplers are designed to analyze gases.
b. Sealed glass tubes and passive samplers are filled with a reagent specifically
sensitive to a target gas.
c. If the target gas is present in an air sample drawn through the tube, a color change
will occur in the tube’s reagent layer.
2. Electrochemical sensor instruments – i.e. oxygen sensor
a. Industrial hygiene work – assessing the high exposure areas in the workplace
b. Emergency response – immediate results to determine what is in air
c. Confined space entry – are oxygen levels at a safe level
d. Measures one or more gases - Examples of gases monitored: carbon monoxide
(CO), carbon dioxide (CO2), hydrogen sulfide (H2S), oxygen (O2), ammonia (NH3),
cyanide (CN), nitric oxide (NO), nitrogen dioxide (NO2), sulfur dioxide (SO2), chlorine
(Cl2), LEL, PID
e. Examples of Electrochemical sensor instruments are: Dräger Pac series, MultiRAE
and MiniRAE, Altair, Orion, and Sirius
8
3.
Vapor sensor instruments
a. Photo-ionization
How do PID (photo ionization detectors) work?
R + hv → R- + + e-
where: R = any ionize able chemical
hv = photon of ionizing energy
R+ = ionized chemical
e- = free electron measured by detector
PID Characteristics
i. Sensitivity increases as the carbon number increases
ii. Different lamps are used to monitor classes of chemicals
- 9.5 ev lamp has higher response for aromatics, less for aliphatics
- 10.2 ev lamp responds to >C4 olefins, all aromatics (like benzene), H2S, NH3,
Br2, PH3, AsH3
- 11.7 ev lamp for halogenated compounds (like methylene chloride), methyl
alcohol, formaldehyde
iii. Different chemicals have different ionization potentials therefore choose a lamp
which will allow it to be detected (i.e. benzene as a ionization potential of 9.2 ev
and isopropyl alcohol has an ionization potential of 10.15 ev, so the 9.5 ev lamp
will detect benzene but will not detect isopropyl alcohol)
b. Flame-ionization – all organic compounds respond differently so calibration is
necessary
c. Infrared detector – detects compounds based on their IR response and
compares it to the library of compounds, FTIR instruments can be used to
characterize unknown atmospheres via their library of IR spectrum. Examples of
portable IR instruments are MIRAN, Buck, Thermo Scientific Nicolet, A2
Technology, Environics, Gasmet, and Prism.
9
Below are the IR spectrum of benzene and ethyl alcohol, showing how they have
absorbances at differing wavelengths allowing quantification on those
wavelengths and chemical identification when compared to a spectral library.
Portable Analytical Instruments – on-site analysis used for emergency response and
Homeland Security Monitoring
1. Portable Gas Chromatographs with a variety of detectors use on-site to analyze gas
bags and sampling tubes. Require a technician or chemist to calibrate the instrument
and perform the analysis. Provides quantitation of results.
2. Portable FTIR detectors used on-site to sample air directly or to analyze gas bags and
sampling tubes. Require a technician or chemist to calibrate the instrument and perform
the analysis. Provides quantitation of results and some identification of unknowns.
3. Portable GC/mass spectrometers detectors used on-site to sample air directly or to
analyze gas bags and sampling tubes. Require a technician or chemist to calibrate the
instrument and perform the analysis. Provides quantitation of results and identification of
unknowns.
10
Portable X-ray Fluorescence for detection of metals
1. Direct analysis of dust for metals based on their x-ray fluorescence.
2. NIOSH Method 7702 and OSHA Method OSA-1 for Lead were made using the Niton
instrument which uses x-ray fluorescence to detect lead and other metals. A
modification of these methods are used to determine metals present at hazardous waste
sites, for accident response, and for Homeland Security Response.
Figure 1. Illustration of X-Ray Fluorescence,
the x-ray shines onto the surface and the
atoms refract the x-ray causing it to fluoresce
which the detector senses.
Air sampling
Vapors
•
Vapors collected using sampling tube, diffusive sampler, or coated filter
•
Tube sampling at a rate of 0.05 L/min to 0.2 L/min
•
Diffusive sampler sampling rate unique for each sampler and analyte
IAQ Organic Vapors – Minican OSHA PV2120
1. Sub ppm levels of 63 volatile organics
–
OSHA PV2120/EPA TO-15
–
Quantitative Analysis
–
5 ppb LOD for most compounds
2. Library search for tentative identification compounds (115 K spectral entries)
–
Estimated concentration only
–
Qualitative identification
3. Sampling times for grab to 24 hrs. available
Total air concentration > 25 ppm
11
Sampling Considerations with Solid Sorbent Collection
1. Humidity – affects absorption of analyte as it can absorb onto active sites and prevent
analyte from absorbing
2. Flow rate – higher flow rates can affect absorption and cause breakthrough – for
tubes<0.2 L/min, use maximum flow rate when doing ceiling, peak or STEL sampling,
and minimum flow rate when doing TWA sampling
3. Temperature – high temperatures force absorbed analyte off the media, so do not store
collected samples in the trunk of your car as it can have temperatures above 150 °F in
the summertime.
4. Concentration of analyte in air – capacity of tube is usually measured at 2 X PEL, if
workplace is concentration higher, collect a smaller air volume
1. Flexible sampling rates chosen by user
2. Wide variety of sampling media
3. Simultaneous use of two or more media types
a. Splitters can be used to sample with two different media on same pump
b. Wide range of analytes including Vapors, Dust, Aerosols, Metals
1. Labor intensive - limits number of samples taken
–
require some kind of pump
–
require pre and post calibration checks
2. Subject to pump failures
–
batteries and pumps are subject to failure & fluctuation
3. Pumps are expensive
–
can cost over \$1,000 per pump
4. Pumps require regular maintenance
–
requires training and is time consuming
5. Workers don’t like wearing pumps
12
Types of Active Sampling Media for Vapors
1. Charcoal
a. Classic Sampling medium
b. Used for Volatile Organic Compounds
c. OSHA 7 / NIOSH 1500
d. Carbon disulfide or a mixture of carbon disulfide and a polar solvent is desorption
solvent of choice
e. Number of Passive Samplers use charcoal such as Assay charcoal sampler, 3M
3500 or 3520 OVM, and SKC 575-001 Passive Sampler
2. Synthetic carbon
a. Carbosieve SIII, Anasorb 747, Anasorb CMS
b. Used for ketones, highly volatile organics, freons
c. Carbon disulfide or a mixture of carbon disulfide and a polar solvent is desorption
solvent of choice
d. SKC 575-002 Passive Samplers
3. Tenax
a. Polystyrene based polymer
b. High surface area
c. Very unreactive
d. Compounds with boiling points between 50 and 200 °C.
e. Very good for thermal or solvent desorption
4. Silica gel
a. Used for very polar compounds
–
Alcohols, Organic Acids, Amines
b. Treated with derivatizing agents for reactive compounds
–
Aldehydes, Ammonia, Cyanoacrylate, Anhydrides, Azides
13
a. Made of polymeric resins, and consist of several different types which are non-polar
Chromosorb 104, Chromosorb 106, and Chromosorb 108
b. Used for:
–
XAD-2: poly aromatic hydrocarbons(PNAs or PAHs); polychlorinated biphenyls
(PCBs or Arochlors), pesticides, and herbicides
–
XAD-4: organic peroxides such as MEK peroxide
–
XAD-7: phenol, cresol, pesticides, and herbicides
–
Chromosorb 104: butyl mercaptan
–
Chromosorb 106: naphthalene
–
HMP (2-Hydroxymethyl piperidine) coated XAD-2 – aldehydes such as
acetaldehyde, formaldehyde
–
p-Anisidine coated XAD-2 – Maleic anhydride
–
NITC (Naphthylisothiocyanate) coated XAD-2 – primary and secondary amines such
as ethyl amine, diethylene triamine, diethanolamine
–
Phosphoric acid coated XAD-7 – cyanoacrylates, amines such as triethylamine
–
7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-CL) coated XAD-7 – primary and
secondary amines
Diffusive Sampler Sampling Considerations
1. Humidity – affects absorption of analyte because it can take up absorption sites leaving
less available for the analyte, also it may trap the analyte behind a water microbubble
requiring the use of a polar solvent in the desorption solvent to dissolve the water so the
analyte can be dissolved in the desorption solvent.
2. Flow rate – flow rate or sampling rate defined by sampler therefore minimum sampling
times must be followed, otherwise the amount of analyte collected will be below the limit
of quantitation or reporting limit of the analysis.
3. Minimum air flow in room needs to be 0.2 m/s for the analyte to diffuse to the badge and
be collected. This will occur in most workplaces with good ventilation. When the air
exchange rate is low, such as in a home, the sampling rate is affected due to lack of
diffusion to the sampler of the analyte, due to sampler starvation. In these cases a
“dead air” sampling rate needs to be used, which is lower than the published sampling
rate, due to the slower diffusion of the analyte.
14
4. Temperature – high temperatures force absorbed analyte off the media, so do not store
collected samples in a hot place such as the trunk of your car.
5. Concentration of analyte in air – capacity of diffusive samplers is usually measured at 2
X PEL, if your workplace is higher, collect for a shorter time, and if you have humidity
higher than 80% collect for a shorter period of time because the water vapor will
decrease the capacity of the sampler.
6. Pressure – lab needs to know the uncorrected barometric pressure to give accurate
results, so get the uncorrected barometric pressure from the local weather service, or
calculate the pressure from the elevation. The barometric pressure reported on the local
weather forecast is corrected to STP and cannot be used in the calculation of ppm. The
elevation for any city can be found at www.airnav.com . The elevation (Elev) in feet of
the worksite can be used to calculate the typical barometric pressure (P) in mm Hg using
the following equation:
[
Elev x 1.6470 x 10-3
P = 760 1 295.20 x (1+ Elev x 4.9787 x 10
-8
]
6.3222
The above equation is an adaptation of the atmospheric model equation used in the U.S.
Standard Atmosphere, 1976 using a higher average effective sea-level screen
temperature (295.20 K) and lower temperature lapse rate (5.4 K/km) typically observed
over land surfaces within the northern latitudes of the U.S. (19o N to 61o N). For most of
the U.S., the barometric pressures obtained with this equation are better estimates of
observed station pressures than the 1976 model, and deviate from mean annual station
pressures by about 0.24% RSD (percent relative standard deviation) for elevations
below 4,300 ft. and 0.52% RSD for elevations below 30,000 ft.
1. Time efficient - Reduces labor in sampling
2. Convenient – Free the IH to do other things
3. Representative – facilitates full-shift sampling with normal worker activity
4. Small and intrinsically safe
5. Can be used by relatively untrained personnel
6. Promoted as equivalent, alternative, supplemental to active sampling
15
1. Sampling rates are fixed by sampler geometry therefore minimum sampling times must
be followed, otherwise the amount of analyte collected will be below the limit of
quantitation or reporting limit of the analysis
2. Method validation is expensive. Actual sampling rates vary from theoretical sampling
rates by up to 17%, and actual sampling rates must be determined in the laboratory with
known test atmospheres. OSHA has a policy that only diffusive samplers which have a
validated method can be used for citation purposes. All others can be used for
screening purposes but active samples must be taken for citation purposes.
3. Sampling rates are low compared to active sampling methods, so minimum sampling
times need to followed
4. Only works for gases and vapors
5. They begin to sample immediately when packaging materials are opened and continue
to sample until placed in packaging materials, therefore care must be used when making
blank samples and calculating the time on/off of the sample.
How do Diffusive Samplers work? (Diffusive Samplers are also known as Passive
Samplers or Monitors)
1. Samplers work by Fick’s law of diffusion, in which the analyte diffuses towards the
sampler, absorbs into the media of the diffusive sampler, and surrounding analyte
diffuses into the the place where the absorbed analyte was.
2. The rate at which a VOC is adsorbed is based on the packing in the sampler and is a
fixed constant, as long as a minimum air flow in the room is maintained so the analyte
can diffuse towards the badge. In a room with dead or low air flow the analyte may not
be able to diffuse towards the badge to be absorbed, which is called sampler starvation.
3. If we know how long the sampler was used and the uptake rate for a particular
compound
4. We can calculate the average concentration over the sampling period using he time
sampled, temperature, and pressure. If the temperature is unknown it creates an
additional ±3% error, and if the pressure is unknown it is an additional ±7.7% error.
External Air Flow
Sampling Rate = ADC / L (ml/min)
Where:
sampler
A = Area of Opening
L = Length of Diffuser
D = Fick’s Law Const
C = Analyte Level in ppm
Figure 3 Diagram of how a diffusive sampler works
16
Part 3 – Air Sampling of Aerosols
Aerosol Types
1. Fibers - Fibers are elongated particles with length much greater than width, with an
aspect ratio, ratio of length to width, which is greater than 3:1. Fibers may be naturally
occurring, like plant fibers and asbestos, or man-made like fiberglass. Asbestos is the
most common fiber sampled in the industrial hygiene environment.
2. Mists - cloud of vaporized liquid or droplets usually 0.1 to 100 µm produced from liquid
by mechanical processes such as splashing, bubbling, or spraying. In the health care
setting the mist droplet aerosols produced by the coughing or treatment of infected
patients.
3. Fogs – Fogs are droplet aerosols formed by condensation from the vapor phase. The
droplets are 1 to 10 µm. While mists may settle toward the ground, fogs appear to
remain suspended in the air.
4. Smokes – Smokes are complex mixtures of particulates and droplets resulting from
incomplete combustion. Examples of smokes are tobacco smoke and diesel exhaust.
The particle size is 0.01 to 1 µm in diameter; but may contain agglomerates which may
be larger.
Aerosol Dust Sizes
1.
2.
3.
4.
Total Dust/Nuisance dust – 1 to 30 µm.
Inhalable Dust – d50 100 µm (d50 = 50% cut-point)
Thoracic Dust - d50 10 µm
Respirable Dust - d50 4 µm; ACGIH changed the median cut point from 3.5 to 4 in 1993
Aerosol Sampling
1. Sampled on filter in cassette or IOM
2. Flow rate 1 L/min or higher dependant upon the type of samples taken – respirable dust
sampling rate dependant upon type of cyclone used
3. 25 mm or 37 mm cassettes
4. Non-conducting cassettes used for asbestos sampling
17
Cyclone sampler
A cyclone sampler is necessary to sample respirable particulate in the aerodynamic size range
applicable for analysis.
Figure 2. Some cyclone samplers. (Key: a) Nylon; b) GK 2.69; c) SKC; and d) Higgins Dewell)
CFR 1910-100
Aerodynamic diameter µm
Percent passing selector
2
90
2.5
75
3.5
50
5.0
25
10
0
Types of filters
1. Mixed cellulose ester (MCE) – metals, dust, asbestos
2. Polyvinyl chloride (PVC) – hexavalent chromium (Cr (VI)), dust
3. Polytetrafluoroethyene (PTFE) – polynuclear aromatics (PNAs), asphalt fumes
4. Glass fiber – PNAs, pesticides, pharmaceuticals
5. Polycarbonate – dust, hexavalent chromium (Cr (VI)
6. Quartz – diesel exhaust, Cr (VI)
18
Blanks
1. Field Blanks - Blank samples are required for each requested analysis, and for each lot
number of sampling media. Prepare field blanks during the sampling period for each
type of sample collected. OSHA requires one field blank for up to 20 samples for any
given analysis/sampling period except for asbestos, which requires a minimum of two
field blanks, even for a single asbestos sample. NIOSH requires two field blanks for
every 10 samples taken. Field blanks (e.g., charcoal tubes, filters) should be opened in
the workplace but not used to take samples, and should be capped as soon as possible
after opening to prevent exposure to the workplace air. They should be handled, stored,
and shipped in the same manner as other sampling media used in sampling air
contaminants, with the exception that no air is drawn through them. Diffusive samplers
should be briefly opened in the field in an area on-site where no contamination is
expected and then immediately resealed with manufacturer's materials. Diffusive
samplers begin to sample as soon as they are opened and continue to sample until they
are sealed.
–
Taken into the field
–
Handled the same ways as field samples
–
Number specified by analytical method
–
Not to be used to calibrate pumps
–
Passive monitors are opened and immediately closed to prevent
contamination
2. Media blanks
–
Unopened new samplers
–
Sent with field samples
–
Not usually taken into the field
19
Calculations
1. Air volume calculation:
2.
Where:
Flow rate × time = air volume
ppm = parts per million
Example: An IH sampled for 100 minutes at a flow rate of 0.2
mg = milligrams
L/min, what is the air volume?
L = liters
0.2 L/min × 100 min = 20 L
m3 = cubic meter
Calculation of ppm of a gas in air:
MW = molecular weight
of analyte
ppm 
µg = micrograms
Vgas (10 6 )
Vair
3
3. Calculation of mg/m :
µg analyte(mg/1000µg)
= mg/m
3
3
air volume in L (m /1000L)
Labs often report the amount of analyte found in micrograms (µg) and 1000 µg = 1 mg.
1000 L = 1 m
3
Example: The chemist determined that an XAD-7 tube contained 250 µg phenol. The IH took a
3
20 L air volume. What is the mg/m of phenol?
250 µg phenol(mg/1000µg)
= 12.5 mg/m
3
3
20 L (m /1000L)
20
3
4. Calculate ppm from mg/m (the molar volume at NTP is 24.45):
ppm ( MW )
mg g


3
L
24.45
m
ppm 
24.45(mg / m 3 )
MW
Example: What would be the ppm phenol in the above example? The molecular weight of
phenol is 94.11.
ppm 
24.45(12.5mg / m 3 )
94.11
ppm = 3.25 ppm
ppm can also be calculated by the following equation:
ppm 
24.45( g )
MW ( L)
Example: The chemist determines that there is 10500 µg toluene on a charcoal tube. The IH
says that he collected an air volume of 11.4 L. The molecular weight of toluene is 92.14. What is
the ppm toluene in the sample?
ppm 
24.45(10500g )
92.14(11.4 L)
ppm = 244 ppm
21
5. AIHA requires all certified labs to report the uncertainty of the analysis
a. May be reported as error or accuracy limits
b. Sampling error of the pump calibration must be added if lab has not added it to
the uncertainty (lab will tell you on the report if the pump error has been added
c. OSHA includes pump error in with analytical error and reports it as SAE
(sampling and analytical error)
d. Diffusive samplers have a Sampling Rate Variation (SRV) instead of a pump
error. The SRV is unique to each sampler design and is slightly higher than the
±5% pump error. Examples of SRV are:
–
3M 3520 OVM:
±6.4%
–
Assay Chemdisc
±7.7%
–
SKC 575 Series:
±8.7%
–
SKC UMEX
±8.1%
–
±7.5%
Example: Calculate the uncertainty of the example above assuming a pump error of
±5% and the lab reported an uncertainty of 0.087 or 8.7%.
Uncertainty = 10.03%=0.10 in decimal form
6. The severity of an exposure is the amount of exposure corrected for the uncertainty and
compared back to the PEL or TLV. OSHA cites on severities over 1.
Severity =exposure result/PEL – uncertainty (in decimal form)
Example: calculate the severity of the toluene example above:
Severity = 244ppm/200 ppm – 0.10 = 1.12 since this number is >1, an overexposure has
occurred
22
7. Determining the minimum air volume that needs to be sampled:
L
24.45( g )
MW ( ppm)
Example: A detector tube indicates that the worker is exposed to 45 ppm methylene
chloride while pouring methylene chloride from the drum to the dip tank. The task takes
5 minutes to perform. The lab has a LOQ (limit of quantitation) of 2 µg for methylene
chloride using the ORBO-91 tube, which is sampled at a flow rate of 0.05 L/min. Can
you sample for 5 min and still get a result for methylene chloride above the lab’s LOQ?
The molecular weight of methylene chloride is 84.93.
L
24.45(2g )
84.93(45 ppm)
min 
L
L / min
L  0.128L
min 
0.128L
0.05L / min
min  2.56 min
You can sample for 5 min and have a reliable result.
8. Calculating Time-Weighted Averages (TWAs)
Cf 
C1T1  C 2T2  C3T3 ...  C nTn
Tf
where Cf = final concentration
C1 = concentration of first sample
T1 = time of first sample
C2 = concentration of second sample
T2 = time of second sample
Cn = concentration of nth sample
Tn = time of nth sample
Tf = time of all samples
Example: An IH sampled a worker for 2-butoxyethanol and the lab reported the
following results: Sample A 21.2 ppm for 120 minutes; Sample B 34.1 ppm for 150
minutes; Sample C 32.8 ppm for 100 minutes; and Sample D 24.9 ppm for 110 minutes.
What is the TWA?
21.2 ppm(120 min)  34.1 ppm(150 min)  32.8 ppm(100 min)  24.9 ppm(110 min)
480 min
C f  28.5 ppm
Cf 
Example: An IH sampled a worker for toluenel and the lab reported the following results:
Sample A 190 ppm for 40 minutes; Sample B 240 ppm for 150 minutes; Sample C 210
23
ppm for 100 minutes; and Sample D 221 ppm for 110 minutes. What is the TWA for the
actual time sampled and for an 8 hour (480 min) exposure?
190 ppm(40 min)  240 ppm(150 min)  210 ppm(100 min)  221 ppm(110 min)
400 min
CTWAactual  222 ppm
CTWAactuL 
190 ppm(110 min)  240 ppm(150 min)  210 ppm(100 min)  221 ppm(110 min)  0 ppm(80 min)
480 min
CTWA480 185 ppm
CTWA480 
9. Calculation of Threshold Limit Values (TLVs) for a mixture with a common health
effect
FTLV 
C
C
C1
C
 2  3 ...  n
TLV1 TLV2 TLV3
TLVn
Example: A worker exposure was 0.3 ppm benzene, 16 ppm styrene, and 67 ppm
xylene. The TLVs are: benzene 0.5 ppm, styrene 20 ppm, and xylene 100 ppm. What is
the mixture TLV?
FTLV 
0.3 16 ppm 67 ppm


 2..07
0.5 20 ppm 100 ppm
10.Calculation of TLVs for Liquid mixtures
Where:
PTLV 
1
P1 = percentage of first analyte in
decimal form
P
P
P1
P
 2  3 ...  n
TLV1 TLV2 TLV3
TLVn
To obtain the percentage in decimal form
divide the percentage with 100%:
decimalfor m 
analyte %
100%
P2 = = percentage of second analyte
in decimal form
Pn == percentage of first analyte in
decimal form
TLV1 = TLV of first analyte
Example: A worker is using a mixture of 55%
stoddard solvent (TLV 525 mg/m3), 35%
toluene (TLV 188 mg/m3), and 10% xylene
(TLV 434 mg/m3),. What is the TLV of the
mixture?
24
TLV2 == TLV of second analyte
TLVn == TLV of nth analyte
FTLV 
1
 316mg / m 3
0.55
0.35
0.10


525mg / m 3 188mg / m 3 434mg / m 3
c. OSHA calculation for silica OSHA General Industry PEL for Respirable Dust Containing
Quartz
PEL 
10
in mg 3
m
%Quartz  2
the general PEL for respirable dust containing Quartz, and/or Cristobalite, and/or
Tridymite.
PEL 
10
in mg 3
m
%Quartz  2(%Cristobalite)  2(%Tridymite)  2
Currently the construction standard is only expressed in millions of particles per
cubic foot (mppcf).
PEL 
250
% Quartz  5
in terms of mppcf
To convert exposures from mg/m3 to mppcf multiply the exposure in mg/m3 by
10. The following calculates the exposure in the example above using the
Construction Standard:
PEL (Construction Standard) 
250 mppcf
%Quartz  2(%Cristobalite)  2(%Tridymite)  5
Example: A single glass-fiber filter and personal sampling pump were used to sample for
carbaryl for an 8-hour period. The SLTC reported 6.07 mg/m3. The SAE for this method
is 0.23. The PEL is 5.0 mg/m3.
Step 1. Calculate the exposure severity.
Y = 6.07/5.0 = 1.21
Step 2. Calculate confidence limits.
LCL95% = 1.21 - 0.23 = 0.98
Because the LCL95% does not exceed 1.0, noncompliance is not established.
The UCL95% is calculated:
UCL95% = 1.21 + 0.23 = 1.44
25
Step 3. Classify the exposure.
Because the LCL95% < 1.0 and the UCL95% > 1.0, classify as possible overexposure.
See the Silica Calculator on OSHA’s website at
http://www.osha.gov/SLTC/etools/silica/compare_to_limit/genius/genius.html
d. Extended Work Shifts (from OSHA Technical Manual
(http://www.osha.gov/dts/osta/otm/otm_toc.html ):
Compliance officers can choose one of two approaches for employees who work
extended work shifts beyond 8 hours. The choice taken will depend on the nature of the
hazardous chemical and the work activity being performed.
1.
2.
The first approach is to sample what the compliance officer believes to be the worst
continuous 8-hour work period of the entire extended work shift.
The second approach is to collect multiple samples over the entire work shift.
Sampling is done so that multiple personal samples are collected during the first 8hour work period and additional samples are collected for the extended work shift.
Unless a compliance officer is dealing with lead, the employee’s exposure in this
approach is calculated based upon the worst 8-hours of exposure during the entire
work shift. Using this method, the worst 8–hours do not have to be contiguous.
Example: for a 10-hour work shift, following established sampling protocol as per the
CSI file, ten 1-hour samples or five 2-hour samples could be taken and the eight
highest 1-hour samples or the four highest 2-hr samples could be used to calculate
the employee's 8-hour TWA, which would be compared to the 8-hour TWA-PEL.
26
Analytical Industrial Hygiene Chemistry – Sample Analysis
Atomic absorption spectroscopy (AAS), graphite furnace atomic absorption
(AAS-GF), Inductively-Coupled Plasma (ICP), Inductively-Coupled Plasma/mass
spectrometry (ICP/MS)
These instruments are used to analyze for metals and metalloid salts. Only specific metals can
be analyzed by AAS, therefore most labs use an ICP or ICP/MS to analyze for multiple metals,
such as solder fume. ICP/MS instruments can analyze all elements in the Atomic Table but are
more expensive and so the analysis may be more expensive. The sample is dissolved or
digested by boiling in a single or multiple acids (nitric acid, hydrochloric acid, sulfuric acid,
hydrofluoric acid, or perchloric acid), with the acid or mixture chosen for the specific mixture
being analyzed as different metals require different acid(s) to completely dissolve them. The
sample is cooled, diluted with water, and analyzed on the appropriate instrument by placing a
known aliquot of the sample in the flame or plasma and measuring the absorption or emission at
specific wavelengths characteristic for each metal. Analytical standards of several
concentrations are first analyzed to establish a calibration curve for each metal being analyzed,
and then the sample is introduced and quantitated. Analytical standards are analyzed
periodically throughout the analysis, along with quality control samples to verify the validity of
the analysis. According to Beer’s Law the response is proportional to the concentration.
Figure 4 A diagram of the AAS. In an ICP or ICP/MS the flame is a plasma.
Resonance Lines,λR (nm) , For Some Elements
200
400
As Pb Hg Mg Cu Zr Ca
600
Ba
Na
27
Li
800
K
Cs
X-ray diffraction (XRD)
X-ray diffraction is used to analyze silica samples. The x-rays beam shines on the sample and
the x-rays are diffracted off at differing angles depending on the crystalline structure of the silica
on the sample, allowing for differentiation of the differing forms of silica and quantification of
each form. The detector measures the three angles occurring from the x-rays bouncing off the
crystalline silica. Amorphous silica does not contain a crystalline structure therefore it cannot be
detected by this form of analysis. The chemical formula SiO2 describes the composition but
not the structure of the silicas. Structurally, silica minerals consist of networks of "SiO4/2" units.
Four oxygen atoms are located at the four corners of a tetrahedron with a silicon atom in the
center. Each O counts as ½ atom because it is bonded to Si in an adjacent tetrahedron forming
a network that extends throughout the entire crystal. Bonding is covalent (electrons are shared
between atoms). A piece of quartz crystal is a single huge molecule. The forms of silica
detected, differentiated, and quantitated by x-ray diffraction are: quartz, cristobalite, tridymite,
coesite, and stishovite. The methods which use x-ray diffraction for the anaklysis of silica are
NIOSH Method 7500 and OSHA Method ID-142. Analytical standards of several concentrations
are first analyzed to establish a calibration curve, and then the sample is introduced and
quantitated. Analytical standards are analyzed periodically throughout the analysis, along with
quality control samples to verify the validity of the analysis.
Figure 5 A diagram of the diffraction of the x-rays by the silica crystal following Bragg’s Law.
28
Figure 6 Here is a typical x-ray diffractiogram of quartz. Note the peaks mark in blue at 26.6 degrees
and 21.9 degrees. Those are the primary and secondary quartz peaks.
Other methods for analyzing silica are NIOSH 7602 which used infrared spectroscopy and
NIOSH 7601 which uses colormetric analysis.
29
Ion Specific Electrodes (ISE)
Ion specific electrodes are used to analyze the specific ion they are designed to detect. A
calibration curve is prepared by analyzing several concentrations of analytical standard and the
samples are analyzed and quantitated from the analytical curve. Analytical standards are
analyzed periodically throughout the analysis, along with quality control samples to verify the
validity of the analysis. Examples of ion specific electrodes are: Ammonium (NH4+), Bromide
(Br-), Chloride (Cl-), Cyanide (CN-), Fluoride (F-), Iodide (I-), Nitrate (NO3-), Nitrite (NO2-),
Perchlorate (ClO4-), Sulphide (S-), Thiocyanate (SCN-).
Infrared Spectroscopy (IR)
Oil mist analyzed by Infrared spectroscopy (IR). A calibration curve is made from analyzing
analytical standards of several different concentrations. The samples are analyzed and
compared to the calibration curve to determine the amount of oil mist collected on the filter.
Analytical standards are analyzed periodically throughout the analysis, along with quality control
samples to verify the validity of the analysis.
Silica samples are analyzed by IR following NIOSH 7602.
Gas chromatography (GC)
Organic chemicals which can be vaporized at temperatures below 300 °C can be analyzed by
gas chromatography (GC) with flame ionization detector (FID), electron capture detector (ECD),
thermal conductivity detector (TCD), flame photometric detector (FPD), nitrogen-phosphorous
detector (NPD), discharge ionization detector (DID), or mass selective detector or mass
spectrometer detector (MSD). There is carrier gas (usually helium or hydrogen) flowing through
the instrument from the injection port to the detector. The sample is introduced into the injection
port by the autosampler via syringe injection, where it is flash heated to vaporize the analytes
present, and the carrier gas carries these chemicals onto the column. The analytes are
separated on the column due to the interaction between the analytes and the coating on the
column along with the temperature program which heats the oven containing the column. The
analytes enter the detector and a response is recorded by the recorder or computer as peaks.
The response of the detector is different for each analyte and is proportional to the amount of
analyte present. The column can be packed or capillary, with the liquid phase coated on a
substrate in the packed column and the liquid phase bonded on the walls of the capillary
column. The instrument is calibrated by analyzing analytical standards of several different
concentrations to form the calibration curve. The response of the analyte in the sample is
compared to this calibration curve to determine the amount of analyte present. Analytical
standards are analyzed periodically throughout the analysis, along with quality control samples
to verify the validity of the analysis. While a charcoal tube may be the collection media for
several analytes, there may be differing desorption solvents for two or more of those analytes,
so check with your laboratory before sampling to determine if you need to take more than one
sample. The desorption solvent dissolves the analyte off the media into solution so it can be
analyzed. Many air sampling guides list the solvent(s) which are used for desorption and can
be used to determine which analytes can be requested together on the same tube.
30
autosampler
Carrier gas
entering
instrument
detector
injection
port
Recorder or
recorder
computer
column
oven
Figure 7 A schematic of a gas chromatograph.
Figure 8 A typical chromatogram from a gas
chromatograph using a flame ionization detector.
The extraction solvent is 99:1 carbon disulfide:N,Ndimethyl formamide (DMF) with p-cymene as
internal standard. The peaks are identified as: (1)
CS2; (2) benzene in CS2; (3) isoamyl acetate; (4) namyl acetate; (5) p-cymene; and (6) DMF.
31
GC with Flame Ionization Detector (GC-FID)
GC-FID is used for most charcoal tube analyses and for many of the other air sampling tube
analyses as the FID is a universal detector which can detect many analytes over a large
dynamic range. Examples of analytes which can be analyzed by GC-FID are: acetates
(such as butyl acetate, ethyl acetate, etc) alcohols (such as ethyl alcohol, isopropyl alcohol,
etc.), aliphatics (such as hexane, octane, naphthas, etc), aromatics (such as benzene,
toluene, xylene, etc), cellosolves (such as 2-butoxyethanol, cellosolve, propylene glycol
ethyl ether, etc.), halogenated hydrocarbons (such as methylene chloride,
tetrachloroethylene, etc), ketones (such as 2-butanone, methyl amyl ketone, 2-hexanone,
etc), and polynuclear aromatics, some organic acids. While a charcoal tube may be the
collection media for several analytes, there may be differing desorption solvents for two or
more of those analytes, so check with your laboratory before sampling to determine if you
need to take more than one sample. The desorption solvent dissolves the analyte off the
media into solution so it can be analyzed. Many air sampling guides list the solvent(s) which
are used for desorption.
GC with Photoionization Ionization Detector (GC-PID)
GC-PID is used to analyze ethylene oxide, tetraethyl lead, and tertramethyl lead. The
correct lamp must be chosen as the ability of the detector to detect compounds is based on
the voltage of photons which will be absorbed by the compound and is different for differing
compounds.
GC with Nitrogen-Phosphorous Detector (GC-NPD)
The NPD detects only compounds containing a nitrogen or a phosphorous, or a compound
which is derivatized with a chemical containing a nitrogen or a phosphorous. It is more
sensitive than a FID, therefore they are used to detect analytes with small PELs or TLVs.
GC-NPD is used to analyze amines (such as triethylamine, etc), acrolein and formaldehyde
as the 2-(hydroxymethyl)piperidine derivative, anhydrides derivatized with veratryl amine
(such as acetic anhydride, etc), nicotine, pesticides containing nitrogen or phosphorous
(such as aldicarb, malathion, etc), and organic phosphates (such as tricresyl phosphate,
etc).
GC with Electron Capture Detector (GC-ECD)
The ECD detects analytes with a free electron such as halogenated compounds or
compounds containing a double bond, or analytes derivatized with a compound containing a
halogen.. It is more sensitive than a FID, therefore they are used to detect analytes with
small PELs or TLVs. GC-ECD is used to analyze butadiene, ethylene oxide as the 2bromoethanol derivative, pentadiene, chlorodane, pesticides containing a halogen (such as
chlordane, cypermethrin, etc), polychlorinated biphenyls (PCBs), and polybrominated
biphenyls (PBBs).
32
GC with Thermal Conductivity Detector (GC-TCD)
The TCD detects analytes by measuring the differences in thermal conductivity between the
column effluent and a reference gas, made of uncontaminated carrier gas. The most
common carrier gas for this detector is helium, because it is inert and has a very low
molecular weight. It is less sensitive than a FID, and detects lower molecular weight
analytes better than higher molecular weight analytes. GC-TCD is used to analyze for
carbon dioxide, carmonoxide, nitrogen and oxygen.
GC with Flame Photometric Detector (GC-FPD)
The FPD detects sulfur or phosphorous compounds as they are burned in a hydrogen-rich
flame as the sulfur and phosphorous compounds emit light above the flame, and this light is
passed through a filter (535 nm for phosphorous compounds and 393 nm for sulfur
compounds) to a photomultiplier tube and the response id recorded. GC-FPD is used to
analyze mercaptans (such as methyl mercaptan, butyl mercaptan, etc), Pesticides
containing a phosphorous or sulfur (such as DDVP, Diazinon, Fonofos, etc),
organophosphates (tributyl phosphate, etc).
GC with Discharge Ionization Detector (GC-DID)
The DID uses a high voltage electric discharge to create ions from the helium carrier gas,
which ionizes the analytes as they elute from the column and these ionized analytes
produce an electrical current which is measured by the detector. GC-DID is used to analyze
aluminized gas bags for carbon dioxide, carbon monoxide, hydrogen, and methane.
GC with Thermal Energy Analyzer (GC-TEA) or GC with Nitrogen Chemiluminescent
Detector (GC-NCD)
The TEA contains a nebulizer which has enough thermal energy to break the N-NO bond
liberating NO which reacts with ozone to form nitrogen dioxide which is measured by the
resultant chemiluminescent emission. The ozone is formed in a separate part of the
detector. The GC-ECD can detect analytes in the ppb which contain a N-NO bond The GCTEA is used to analyze nitrosoamines and pesticides containing a N-NO bond.
GC with Mass Spectrometer or Mass Selective Detector (GC-MS)
The MS ionizes the analytes as they emerge through the column, breaking the analyte into
characteristic fragments which are separated by their mass-to-charge ratio and detected by
the electron multiplier. GC-Ms is used to analyzed thermal desorption tubes and mini-cans
as they can be analyzed only once therefore it is important to identify the analytes and
quantify the analytes at the same time. GC-MS can also be used, along with a pyrolizer, to
determine the analytes produced when plastics are heated. NIOSH Method 2539 for
aldehyde screening uses GC-MS to detect and identify the aldehydes in the workplace.
Another GC/MS method is EPA Method TO-17, which collects indoor air on Tenax tubes,
which are thermally desorbed and analyzes them by GC-MS to quantify and identify the
analytes present. Analytes with boiling points at or below room temperature will not collect
on the Tenax tubes.
33
High Performance Liquid Chromatography (HPLC)
HPLC is used to analyzed compounds which have very high boiling points or are unstable at
temperatures above room temperature. The instrument consists of an autosampler, injector, a
column for analyte separation, one or more detectors, and an integrator or computer. Instead of
a carrier gas, a mixture of solvents or solvent and water, called a mobile phase, is used to carry
analytes from the autosampler through the column to the detector(s). The analytes are
separated by the column due to their interaction with the solid adsorbent in the column and the
solubility of the analyte in the mobile phase. The one or more detectors can be used to detect
the compound and differentiate it from interferences. The detectors are: electrochemical,
fluorescence, and ultraviolet-visible. The response of the detector is different for each analyte
and is proportional to the amount of analyte present. The instrument is calibrated by analyzing
analytical standards of several different concentrations to form the calibration curve. The
response of the analyte in the sample is compared to this calibration curve to determine the
amount of analyte present. Analytical standards are analyzed periodically throughout the
analysis, along with quality control samples to verify the validity of the analysis.
Solvent
pump
column
detector
recorder or computer
Figure 9 Diagram of a liquid chromatograph or ion chromatograph.
Response (mV)
1
1500
3
500
5
2
4
6
0
5
10
15
Time (min)
Figure 10. A chromatogram of a mixture of aldehyde derivatives of DNPH analyzed by HPLC-UV at 365
nm. (Key: 1 = DNPH, 2 = formaldehyde, 3 = acetaldehyde, 4 = butylaldehyde, 5 = benzaldehyde, and 6 =
glutaraldehyde.)
HPLC-Electrochemical detector (HPLC-EC)
The EC detector detects analytes as they oxidize or reduce producing an electrical current
which is detected by an electrode. Examples are phenols, aromatic amines, ketones,
34
aldehyde, peroxides, and mercaptans.
HPLC-Fluorescence detector (HPLC-FL)
The FL detector measures the emission of light from the analyte, especially from analytes
containing a benzene ring. The wavelengths of the emission are characteristic for each
analyte. Some methods use a derivatizing agent which fluoresce to stabilize analytes which
can react with themselves, such as isocyanates, or to obtain a lower detection limit.
Examples of compounds analyzed by HPLC-FL are isocyanates such as 2,4-toluene
diisocyanate (2,4-TDI), polynuclear aromatics such as benzo (a) pyrene, and aromatic
amines such as p-xylidine-a,a- diamine.
HPLC-Ultraviolet-visible detector (HPLC-UV-vis) or (HPLC-UV) when Ultraviolet
detector only is used
The UV detector measures the UV light absorbance of the analyte as it emerges from the
column. UV-vis is used primarily for measurement of dyes which absorb in the visible range.
The UV detector is especially sensitive to aromatic hydrocarbons (which contain a benzene
ring) and other analytes containing a double bond. Examples of compounds analyzed by
HPLC-UV are polynuclear aromatics (PNAs), peaticides, herbicides, quinines, aflatoxins,
derivatized isocyanates, derivatized aldehydes such as formaldehyde and glutaraldehyde,
pharmaceuticals, and phenols.
35
Ion Chromatography (IC)
IC is similar to HPLC except the analytes are in solution as ionic species and the column
separates the analytes through ion exchange chromatography. The detectors are: conductivity,
electrochemical, and ultraviolet-visible. The response of the detector is different for each
analyte and is proportional to the amount of analyte present. The instrument is calibrated by
analyzing analytical standards of several different concentrations to form the calibration curve.
The response of the analyte in the sample is compared to this calibration curve to determine the
amount of analyte present. Analytical standards are analyzed periodically throughout the
analysis, along with quality control samples to verify the validity of the analysis.
Response (mV)
25
1
15
5
-5
0
2
4
6
8
10
Time (min)
Figure 11 A chromatogram of 500 ng/mL Cr (VI)
analyzed by IC-UV-vis at 540 nm using postcolumn derivatization with 1,5-diphenyl carbazide.
[Key: 1) Cr (VI).]
IC Conductivity Detector (IC-CD)
The CD measures the conductance of the ionic analyte species as it emerges from the
column. Since the mobile phase (also called eluent) is ionic it can give a high conductance
background, therefore this background is removed by use of an ion suppressor, resulting in
greater sensitivity to the analyte. The ion suppressor can be an anion suppressor or a
cation suppressor and the appropriate suppressor is chosen based on the type of species
being analyzed. The CD is used to analyze mineral acids such as hydrochloric acid, nitric
acid, phosphoric acid, andsulfuric acid, sulfite, thiocyanate, small organic acid such as
acetic acid and propionic acid, ammonia, amines, beta-naphthylamine, benzidine,
hydrazines, azoarenes, and aziridines.
36
IC Electrochemical Detector (IC-ED)
The EC detector detects analytes as they oxidize or reduce producing an electrical current
which is detected by an electrode. Examples are azides, cyanide, sulfide.
IC-Ultraviolet-visible detector (IC-UV-vis) or (IC-UV) when Ultraviolet detector only is
used
The UV detector measures the UV light absorbance of the analyte as it emerges from the
column. UV-Vis is used primarily for the analysis of hexavalent chromium which uses a post
column reaction vessel to react hexavalent chromium with 1,5-diphenyl carbazaie to form
the carbazone which is measured at 540 nm in the visible range. Ozone is analyzed by ICUV.
Visible Absorption Spectrophotometry
There are several colorimetric methods used for the analysis of organic compounds, but these
are being replaced by GC, HPLC, and IC methods. The analytes which your lab may use a
colorimetric method are acetic anhydride, ammonia, formaldehyde, hydrazine, nitrogen dioxide,
and phosphine.
37
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