Lesson 8

How can you provide quality assurance

and quality control?

Slide 8-2

QA/QC in radon measurement

• Activities to make sure that radon testing equipment and services meet EPA quality standards

• Goal: to reduce or eliminate errors• Helps clients make well-informed

decisions that affect– Health– Finances

Slide 8-3

QA/QC components• Measuring to assess

– Precision– Accuracy

• Checking and documenting performance of devices

Slide 8-4

PrecisionAre measurements repeatable or consistent when

an identical item is measured several times?

Measurements are precise (close together) but not accurate (not near bull’s eye)

Slide 8-5

AccuracyAre measurements close to the correct or true

value?

Measurements are accurate (in bull’s eye) but not precise (close together)

Slide 8-6

Precise and accuratePrecise• Measurements are

close together

Accurate• Measurements are

in bull’s eye

Slide 8-7

Tests for passive devices

• Duplicates – Measure precision

• Spikes– Measure accuracy

• Blanks– Measure bias (how

far measurements are from accurate)

Slide 8-8

Duplicates(measure precision)

• Make duplicates at least 10% of total number of measurements

• Set out two identical devices that have been stored in the same place– Place side by side,

about 4 inches apart• Leave in place for the

same amount of time

• Label them so that– You know they are

duplicates– Lab will not know they

are duplicates• Ship devices to the lab

together

Slide 8-9

Check duplicate resultsStep How to calculate Example

1Calculate average of two results

Average = Result 1 + Result 2

2

4.3 + 3.9 =20

4.12Calculate relative percent difference (RPD) of two results

RPD = (Result 1 – Result 2) x 100

Average of two results

(4.3 - 3.9) x 100 =4.1

0.4 x 100 =4.1 0

10%

Slide 8-10

Check relative percent difference

If average of 2 results is 4 pCi/L or more, – RPD should be no

more than 25%– If RPD is greater

than 25%, investigate

0%

25%

50%

75%

100%

Slide 8-11

Spikes(measure accuracy)

• Make spikes – At least 3% of total measurements or– At least 3 per year– No more than 6 per month

• Send unexposed device to special lab where it will be exposed to known radon concentration

• Label device so that– You know it is a spike– Lab will not know it is a spike

• Ship exposed device to regular lab

Slide 8-12

Check spike resultsHow to calculate Example

Compare target value and measured value

Target value–Measured valueTarget value

5.7 – 5.2 =5.7

0.09

For spikes at 4 pCi/L or higher, calculated value should be no more than 0.10

If result is higher, investigate

Slide 8-13

Blanks(measure bias)

• Check accuracy by measuring bias– How close is measured value to target

value?• Help determine whether accuracy

has been affected in– Manufacturing– Shipping– Storing– Processing the device

Slide 8-14

Blanks

• Label device so that– You know it is a blank– Lab will not know it is a blank

• Ship unexposed device to lab

• Make blanks at least 5% of total number of measurements

• Unwrap a device but do not open it.

• Leave unopened device in place for standard exposure period

Slide 8-15

Blanks• In theory, blanks should measure 0

pCi/L• In practice, blanks should measure at

lower limit that device can measure• If result is higher, investigate

Slide 8-16

Active devices• Calibrate at least once a year• Check device manual or ask

manufacturer for referral to calibration lab

Slide 8-17

Routine instrument checks

• Check equipment periodically• Include all components

– Batteries– Pumps– Electronics– Airflow

Slide 8-18

Document all tests• Information about

device– Manufacturer – Type/model– Serial or ID number

• Times– Start date and time – Stop date and time

• Exact location of device on diagram of room and building

• Other building information– Type of building– Type of heating

system– Foundation types– Operation of

humidifiers, air filters, electrostatic precipitators, and clothes dryers

• Test conditions

Slide 8-19

Document your QA/QC activities

• QA/QC plan from any lab you use

• For passive devices – Test dates and times– Percentage of tests in

relation to total tests– Label used to identify

QA/QC test– Type of QA/QC

measurement• Duplicates• Spikes• Blanks

• For active devices– Calibration dates and

other details

• Information about device– Manufacturer – Type/model– Serial or ID

number

Slide 8-20

Questions?

Slide 8-21

SummaryQA/QC for passive devices

Type of test

Measures % of total measurements

Duplicate Precision At least 10%

Spike Accuracy At least 3%

Blank Bias/accuracy At least 5%

Slide 8-22

SummaryActive devices

• Calibrate at least once a year

Slide 8-23

SummaryAll devices

• Check all instruments periodically• Document all measurements• Document all QA/QC activities