Lesson 5

What devices do we use to measure

radon?

Slide 5-2

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

Slide 5-3

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 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

Slide 5-4

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

Slide 5-5

Questions?

• About sampling methods

Slide 5-6

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

Slide 5-7

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 5-8

Types of passive devices

• Activated charcoal adsorption• Charcoal liquid scintillation• Electret ion chamber (electrostatic

radon monitor)• Alpha track detector

Slide 5-9

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)

Slide 5-10

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

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 5-11

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 5-12

Passive devicesCharcoal 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 5-13

Passive devicesElectret ion chamber

• Most common: electret-passive environmental radon monitor (E-PERM)

• Use for short-term and long-term tests

Slide 5-14

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

Slide 5-15

Passive devicesElectret 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 5-16

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

Slide 5-17

Passive devicesAlpha track detector

Advantages• Requires no external

power • Inexpensive• Simple to use• Easy to mail• Provides true time-

integrated 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 5-18

Questions?

• About passive measurement devices

Slide 5-19

ActivityHandout 5-1A

Type of device Length of test Advantages Disadvantages

Activated charcoal adsorption

Charcoal liquid scintillation

Electret ion chamber

Alpha track detector

Slide 5-20

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 5-21

Active devices

• Use for short-term tests• Air either diffuses or is pumped into a

counting chamber

Continuous working level

monitor

Continuous radon monitor

Slide 5-22

Active devicesContinuous 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 5-23

Questions?

• About active radon measurement devices

Slide 5-24

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

Slide 5-25

SummarySampling methods

• Time-integrated sampling• Continuous sampling• Grab sampling

Which methods should home inspectors use?Time-integrated and continuous sampling

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

Slide 5-27

Questions?

Slide 5-28

Checkyour understanding

• See handout 5-2