Lesson 5
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Transcript of Lesson 5
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Lesson 5
What devices do we use to measure
radon?
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How long will the test last?
Short-term test2 to 90 days
Long-term test91 to 365 days
Advantage– Provides quick answer
Disadvantage– Does not account for
radon variations from day to day or season to season
Used for most real estate transactions
Advantage– Provides more
information about year-round average radon level
Disadvantages– Takes longer to get
results– Residents forget test is
running
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Sampling methods for radon and radon decay products
1. Time-integrated sampling– Average concentration
over a period of time– Period may range from
a few days (for most home inspections) to a year or more
2. Continuous sampling– Automatic sampling
over set intervals of time
3. Grab sampling– Quick snapshot at a
moment in time– Rarely used in home
inspectionsAdvantages
– Can collect several samples in one day
– Can observe conditions while sampling
Disadvantages– Not certain how well it
correlates with long-term integrated measurement
– Requires additional training and expensive equipment
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Grab sample• Would you
use a grab sample to determine whether a home needs radon mitigation?
• Why or why not?
No, because• It provides only a snapshot or radon
at brief moment in time• We don’t know how well it correlates
with longer-term measurements• Decision about mitigation should be
based on averages over longer periods of time
• EPA does not recommend use of grab samples for pre-mitigation or post-mitigation testing or for follow-up measurements
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Summary of sampling methods
• Time-integrating sampling is usually most useful for home inspections
• Questions?
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Standards for devicesAll devices must meet the requirements of the
National Environmental Health Association (NEHA)or the
National Radon Safety Board (NRSB)
Read and follow the directions of the manufacturer of the device you use
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Types of devicesPassive devices• Do not require
power (electricity or batteries) to operate
• Less expensive• Used in most real
estate transactions
Active devices• Require power to
operate• More expensive• Require calibration
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Types of passive devices
• Activated charcoal adsorption• Charcoal liquid scintillation• Electret ion chamber (electrostatic
radon monitor)• Alpha track detector
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Passive devicesActivated charcoal adsorption
Use for short-term tests • Airtight canister that
contains granular activated carbon is opened
• Radon from surrounding air enters canister and is adsorbed (held on its surface) by charcoal
• At end of test period, canister is sealed and sent to approved lab for analysis
Two types• Open face• Diffusion barrier
(filter over face)
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Passive devicesActivated charcoal adsorption
Advantages • Requires no
external power • Inexpensive• Easy to place• Simple to use • Easy to mail to
lab• Measures over
short time periods
• Gives precise and accurate measurements
Disadvantages• Biased toward end of sampling
period• Works best for short sampling
periods• May be affected by sampling
conditions (temperature, humidity, and drafts)– Sampling conditions during
test period may be unknown• Must be analyzed by approved
lab soon after test period• Difficult to know if device has
been tampered with
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Passive devices:Charcoal liquid scintillation
Use for short-term tests • Small vial containing
activated charcoal is opened
• Radon from surrounding air enters vial and is adsorbed by charcoal
• At end of test period, vial is sealed and sent to approved lab for analysis
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Passive devices:Charcoal liquid scintillation
Advantages• Same as for
activated charcoal adsorption canister
Disadvantages• Same as for activated
charcoal adsorption canister
• Especially: device must be analyzed by approved lab soon after test period
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Passive devicesElectret ion chamber
• Most common: electret-passive environmental radon monitor (E-PERM)
• Use for short-term and long-term tests
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Passive devicesElectret ion chamber
• Electrostatically charged disk (electret) is placed in small chamber
• Radon diffuses into chamber and emits alpha particles during decay
• Alpha particles ionize the air molecules• Ions move to charged surface of electret, thus
reducing its initial charge • Voltage meter measures initial and final voltages• Rate of change of charge is proportional to
concentration of radon in air
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Passive devicesElectret ion chamber
Advantages• Requires no
external power • Provides true
integrated measurements
• Each electret may be reused many times
• Can provide immediate results
Disadvantages• Requires training to use • Must measure and correct for
background gamma radiation• May be affected by high
humidity • Temperature differences
between initial and the final voltage readings may cause errors
• Does not provide evidence of tampering
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Use for long-term tests only• Contains piece of film or
plastic that records impacts (tracks) of alpha particles produced by decay of radon and its decay products
• At end of test period, detector is returned to approved lab– Lab counts alpha tracks on
film and computes radon concentration
Passive devicesAlpha track detector
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Passive devicesAlpha track detector
Advantages• Requires no external
power • Inexpensive• Simple to use• Easy to mail• Provides true integrated
measurements– Not biased toward
most recent exposure– Can measure over long
periods (90-365 days)
Disadvantages• Cannot measure for
short time periods unless radon concentrations are high
• May not provide precise measurement when concentrations are low
• May be affected by sampling conditions– Sampling conditions
during test period may be unknown
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Questions?• About passive measurement devices
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ActivityHandout 5-1A
Type of device Length of test Advantages Disadvantages
Activated charcoal adsorption
Charcoal liquid scintillation
Electret ion chamber
Alpha track detector
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Active devices• Electronic devices• Require power (batteries or electricity) to
operate• Measure and record amount of radon or its
decay products in air at regular intervals– At least once an hour– Results are average of these readings
• Can show changes in radon levels during test period
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Active devices
• Use for short-term tests• Air either diffuses or is pumped into a
counting chamber
Continuous working level
monitor
Continuous radon monitor
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Active devicesContinuous radon monitors
Advantages• Provide results on-site• Give precise, accurate results • Can track real time variations in
radon concentrations• Can measure various time
intervals• Some models record
temperature, humidity, barometric pressure, movement, and other environmental factors
• Can indicate tampering
Disadvantages• Require power to
operate• More expensive• Must be
calibrated regularly
• Require training to operate
• Some are sensitive to humidity
• Some are heavy and bulky
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Questions?• About active radon measurement
devices
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SummaryLength of tests
Short-term test• How many days?
– 2-90• Advantage?
– Provides a quick answer about radon levels
• Disadvantage?– Does not account for
radon variations from day to day or season to season
Long-term test• How many days?
– 91-365 • Advantage?
– Gives more information about year-round average radon levels
• Disadvantage?– Takes longer to get
results
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Slide 5-25
SummarySampling methods
• Time-integrated sampling• Continuous sampling• Grab sampling
Which method do home inspectors most commonly use and why?Time-integrated sampling because it provides quick, accurate answers, which are important for real estate transactions
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Slide 5-26
SummaryTypes of devices
• Passive– Activated charcoal
adsorption– Charcoal liquid
scintillation– Electret ion
chamber (electrostatic radon monitor)
– Alpha track detector
• Active– Continuous radon
monitors– Continuous working
level monitors
Which type of devices do home inspectors most commonly use?Passive
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Questions?
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Checkyour understanding
• See handout 5-2