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Lesson 5
What devices do we
use to measure
radon?
How long
will the test last?
Short-term test
Long-term test
2 to 90 days
91 to 365 days
Advantage
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
– Provides more
information about yearround average radon
level
Disadvantages
– Takes longer to get
results
– Residents forget test is
running
Slide 5-1
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
– Cannot be used in
home inspections
–
–
–
–
Advantages
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
Slide 5-2
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 postmitigation testing or for follow-up
measurements
Slide 5-3
Questions?
• About sampling methods
Slide 5-4
Standards for devices
All 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
Slide 5-5
Types of devices
Passive 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
Slide 5-6
Types of
passive devices
• Activated charcoal adsorption
• Charcoal liquid scintillation
• Electret ion chamber (electrostatic
radon monitor)
• Alpha track detector
Slide 5-7
Passive devices
Activated 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)
Slide 5-8
Passive devices
Activated charcoal adsorption
Advantages
• Requires no
external power
• Inexpensive
• Easy to place
• Simple to use
• Easy to mail to
lab
• Measures over
short time
periods
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
Slide 5-9
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
Slide 5-10
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
Slide 5-11
Passive devices
Electret ion chamber
• Most common:
electret-passive
environmental
radon monitor
(E-PERM)
• Use for short-term
and long-term
tests
Slide 5-12
Passive devices
Electret 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
Slide 5-13
Passive devices
Electret ion chamber
Advantages
• Requires no
external power
• Provides true
time-integrated
measurements
• Each electret
may be reused
many times
• Can provide
immediate
results
Disadvantages
• Requires additional training
to use
• Must measure and correct for
background gamma radiation
• May be affected by high
humidity and dust
• Temperature differences
between initial and the final
voltage readings may cause
errors
• Does not provide evidence of
tampering
Slide 5-14
Passive devices
Alpha track detector
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
Slide 5-15
Passive devices
Alpha track detector
Advantages
• Requires no external
power
• Inexpensive
• Simple to use
• Easy to mail
• Provides true timeintegrated measurements
– Not biased toward
most recent exposure
– Can measure over long
periods (90-365 days)
Disadvantages
• Cannot measure for
short time periods
• May not provide precise
measurement when
concentrations are low
• May be affected by
sampling conditions
– Sampling conditions
during test period
may be unknown
Slide 5-16
Questions?
• About passive measurement devices
Slide 5-17
Activity
Handout 5-1A
Type of device
Length of test
Advantages
Disadvantages
Activated charcoal
adsorption
Charcoal liquid
scintillation
Electret ion chamber
Alpha track detector
Slide 5-18
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
Slide 5-19
Active devices
Continuous
radon monitor
Continuous
working level
monitor
• Use for short-term tests
• Air either diffuses or is pumped into a
counting chamber
Slide 5-20
Active devices
Continuous radon monitors
Advantages
• Provide results on-site
• 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 additional
training to operate
• Some are sensitive
to humidity
• Some are heavy
and bulky
Slide 5-21
Questions?
• About active radon measurement
devices
Slide 5-22
Summary
Length 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
Slide 5-23
Summary
Sampling methods
• Time-integrated sampling
• Continuous sampling
• Grab sampling
Which methods should home
inspectors use?
Time-integrated and continuous
sampling
Slide 5-24
Summary
Types 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
Slide 5-25
Questions?
Slide 5-26
Check
your understanding
• See handout 5-2
Slide 5-27