Transcript Air Monitoring - Brownfields Toolbox

Air Monitoring
Instructional Goal:
Enable participants to recognize the
value of direct-reading instruments in
providing immediate air concentration
results at a hazardous waste site.
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Sampling Methods
 Area
sampling
 involves placing collection devices within
designated areas and operating them over
specific periods of time.
 Personal
sampling
 involves collecting samples from within the
breathing zone of an individual, sometimes
by the individual wearing a sampling device.
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Instantaneous Sample

are collected over brief periods of time
 grab-type sample
 examines stable contaminant
concentrations or peak levels of short
duration.
 require highly sensitive analytical methods
due to the small sample volume
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Air Monitoring Data is used to
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
assess health risks

determine location where PPE must be worn
and correct PPE to wear

determine actual or potential effects on the
environment

select actions to mitigate the hazards

determine the effectiveness of
decontamination activities
Sampling System

sampling instrument or system chosen
depends on a number of factors:
instrument or system efficiency
operational reliability
ease of use and portability
availability of the instrument and
component parts
 information or analysis desired
 calibration requirements
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Air Monitoring Instruments
must be
 portable
 easy
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and rugged
to operate
Air Monitoring Instruments
must be Inherently Safe
 explosion-proof
 intrinsically
 purged
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safe
Air Monitoring Instruments must
give Reliable and Useful Results
 Response
time
 is the length of time the monitor takes from
when it "senses" a contaminant until it
generates data. For direct-reading
instruments, response times may range
from a few seconds to several minutes.
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Air Monitoring Instruments must
give Reliable and Useful Results
 Sensitivity
 defined as the ability of an instrument to
accurately measure changes in
concentration. Sensitive instruments can
detect small changes in concentration.
 It is important to use an instrument with
an operating range that will measure the
ambient concentrations on-site.
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Air Monitoring Instruments must
give Reliable and Useful Results
 Selectivity
 the ability of an instrument to detect and
measure a specific chemical or group of
similar chemicals.
 Interferences from other chemicals can
affect the accuracy of the instrument
reading by producing a similar response.
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Air Monitoring Instruments must
give Reliable and Useful Results
 Accuracy
 the relationship between a true value (i.e.,
the actual concentration of a contaminant)
and the instrument reading.
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Air Monitoring Instruments must
give Reliable and Useful Results
 Precision
 a statistical measurement of
an instrument's ability to
reproduce a reading.
 When an instrument does not
receive routine maintenance
the precision of the readings
may change (become more
random) this can affect the
amount of error in the data
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Bench Calibration
 follow
manufacturer’s directions
for calibration to ensure accurate
field data
 use standard sample of known
concentration for calibration
 adjust the instrument read-out so
that it corresponds to the actual
concentration
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Monitoring Equipment
 Direct-Read
Instruments
 oxygen availability monitor
 combustibility monitor
 toxic atmosphere monitor
 radiation monitor
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Oxygen Indicators

20.8% O2 is normal air

at and below 19.5% O2 in air, O2 deficient
 either displaced by another gas
 or consumed by combustion or reaction

> 23% O2 in air, increased risk of
combustion (possible oxidizer present)
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Combustible Gas Monitor
measures concentration of flammable
vapor or gas in air
 reads in % Lower Explosion Limit (LEL)
 read out is relative to the calibration
gas; therefore, may not show actual %
of LEL
 for use only in normal oxygen
atmospheres
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Flammable
Range
LEL
0% 5%
0%
0%
10%
Action Level
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UEL
15%
METHANE
100%
5%
LEL
METER READING % LEL
Relative Response CGI Meter
methane
100%
80%
pentane
60%
40%
xylene
20%
0%
0%
50%
ACTUAL % LEL
100%
% LEL Policy
The employer will issue work
permits when the % LEL is from 010% LEL.
 When the LEL exceeds 10%,
special approval is required in
order for a work permit to be
issued.
 For all confined space entry
permits, a 0% LEL is required.
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Toxic Atmosphere Monitors
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Colorimetric Indicator Tubes
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Features
 glass tube with
indicating chemical

 chemical specific
 contaminated air
pumped in at predetermined rate
Pre-filter
Cotton Plug
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DETECTOR TUBE
Color Change
Indicating Chemical
on Silica Gel
Limitations
 other chemicals may
interfere with result
 poor accuracy and
precision
 affected by temperature
and humidity
 interpretations vary
 time consuming - 1 to 30
minutes per tube
Cotton Plug
Photoionization Detector
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Features
 Nonspecific gas and vapor
detection for organics and some
inorganics
 Sensitivity is related to the
ionization potential of
compound
 Portable with remote sensing
capabilities
 Response time of 90% in less
than 3 seconds
 More sensitive to aromatic and
unsaturated compounds than
the flame ionization detector
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Limitations
 Does not monitor for
specific gases or vapors
 Cannot detect Hydrogen
cyanide or methane
 Cannot detect some
chlorinated organics
 High humidity and
precipitate will negatively
affect meter response
 Photoionization detectors
are calibrated to a single
chemical
Flame Ionization Detector
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Features
Nonspecific total
hydrocarbon analyzer
Most sensitive to
saturated hydrocarbons
(alkanes), and
unsaturated hydrocarbon
(alkenes)
Portable with remote
sensing probe
Response time of 90% in
2 seconds
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Limitations
Not suitable for inoganic gases
(e.g. chlorine, hydrogen
cyanide, ammonia)
Less sensitive to unsaturated
compounds than PID
Can not use in the presence of
a flammable gas (ignition
source)
Substances that contain
substituted functional groups
(-OH) and (-Cl) reduce the
detector's sensitivity
Aerosol Monitors
 Solids
and liquids can become
suspended in air
 light scatter detector
 piezoelectric crystal mass monitor
 beta attenuation
 Total
particulate amount
 Type not determined
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Sample Problem
Suppose prior analysis has established that
the dust at a certain site contains 5 percent
lead and 1 percent arsenic. During
subsequent monitoring, the concentration of
dust is found to be 2mg/m3.
(% of each)
100
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X
amount of dust= conc of each
present in air
Answer
The concentration of lead and arsenic,
therefore, are calculated to be 0.1 mg/m3
and 0.02 mg/m3 respectively:
0.05 x 2 mg/m3 = 0.1 mg/m3 lead
0.01 x 2 mg/m3 = 0.02 mg/m3 arsenic
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Combination Instruments
 flammable
gas and O2
 trimeters
 four
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gas meters
Radiation Monitoring

Alpha
 Proportion Counters
 Scintillation Counters

Beta and Gamma
 Geiger-Mueller Counters
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