Measuring radon in residential properties How can you provide QA/QC?
Lesson 8: How can you provide quality assurance (QA) and quality control (QC)?
Lesson overview
This lesson explains quality assurance/quality control (QA/QC) and describes the importance of establishing and maintaining a quality assurance program.
Lesson objectives
By the end of this lesson, the learners will be able to:
· Recognize the importance of using a quality assurance/quality control (QA/QC) program
· Identify the two features that are used to assess the quality of radon measurement
· Match the three types of QA/QC tests for passive devices with the features they measure
· Describe the methods associated with each type of test
· List the key documents needed for QA/QC
Introduce the lesson.
Show slide 8-0.
In this lesson, we are going to talk about quality assurance (QA) and quality control (QC). We will consider what these terms mean and why it is important to have and maintain a QA/QC program.
Show slide 8-1.
Explain.
The terms quality assurance and quality control are often used interchangeably. Together, QA/QC in radon measurement refers to all activities to make sure that radon testing meets EPA quality standards. The goal is to reduce or eliminate errors in measurement.
Your clients will make decisions that affect their families’ health and finances on the basis of these tests. To ensure that people can make well-informed decisions, the EPA recommends that everyone who provides radon measurement services should establish and maintain a QA/QC program.
Show slide 8-2.
Explain.
A QA/QC program includes several components:
· Measuring to assess several features that we’ll explain in a moment:
o Precision
o Accuracy
· Checking and documenting the performance of the devices you use to measure radon.
Show slide 8-3.
Explain.
If measurements are precise, they are repeatable or consistent when an identical item is measured several times.
To understand precision, think about a bull’s eye. Measurements are precise when they are close together.
In this illustration, the measurements are precise (close together) but not accurate (because they are not near the bull’s eye.
Show slide 8-4.
Explain.
Measurements are accurate when they are close to the correct or true value.
In this illustration, the measurements are accurate (in the bull’s eye) but not precise (because they are not close together).
Show slide 8-5.
Explain.
This illustration shows measurements that are both precise (close together) and accurate (in the bull’s eye).
Radon measurements should be both precise and accurate.
Show slide 8-6.
Explain.
If you are using passive testing devices, you should conduct three types of measurement tests to ensure that your results are reliable:
· Duplicates are used to measure precision
· Spikes are used to measure accuracy
· Blanks are used to measure bias (how far off the measurements are from accurate)
Show slide 8-7.
Explain the duplicate methods
As we just said, duplicates measure precision, or how close together measurements are.
• Make duplicates at least 10% of the total number of measurements
• Set out two identical devices that have been stored in the same place
o Place side by side, about 4 inches apart
• Leave in place for the same amount of time
• Label them so that
o You know that they are duplicates
o The lab cannot tell that they are duplicates
• Remove the two devices and ship to the lab together
Show slide 8-8.
Explain
To check precision, check the duplicate results.
First, calculate the average of the two results.
Average = Result 1 + Result 2
2
Next, calculate the relative percent difference (RPD).
RPD = (Result 1 – Result 2) x 100)
Average of two results
Show slide 8-9.
Explain.
If the duplicate pairs have an average of 4pCi/L or more, the RPD should be no more than 25%.
If the RPD is greater than 25%, investigate the source of the difference.
Show slide 8-10.
Explain spikes.
Spikes, also known as spiked samples or exposure measurements, measure accuracy.
• Make spikes
o At least 3% of the total number of measurements or
o At least 3 per year
o No more than 6 per month
• Send an unexposed device to a QA/QC lab where it will be exposed to a known radon concentration in a special calibration chamber.
o Ask device manufacturer to recommend a QA/QC lab
o The value provided by the QA/QC lab is the known (or target) value
• Label the device so that
o You know that it is a spike
o The analytical lab will not know it is a spike
• Ship the exposed device to the analytical lab.
Show slide 8-11.
Explain.
To check accuracy, check the spike results from the analytical lab.
Compare the target value of the spike from the QA/QC lab with the measured result from the analytical lab:
Target value – Measured value
Target value
• For spikes at 4 PCi/L or higher, the calculated value should be no more than 0.10.
• If the result is higher, investigate the cause.
Show slide 8-12.
Explain blanks.
Blanks are unexposed devices that are measured as another way to check accuracy. Blanks actually measure bias, or how close the measured value is to the target value.
Blanks can help determine whether accuracy has been affected in
• Manufacturing
• Shipping
• Storing
• Processing the device
Show slide 8-13.
Explain.
To measure bias with blanks,
• Make blanks at least 5% of the total number of measurements.
• Unwrap a device but do not open it.
• Leave unopened device in place for standard exposure period.
• Label the device so that
o You know that it is a blank
o The lab cannot tell that it is a blank.
• Ship the unexposed device to the lab.
Because they have not been exposed to radon, blanks should (in theory) measure 0 pCi/L. In fact, however, they may read slightly above 0. However, the results should be at the lower limit of what the devices can measure.
If the measurement is higher, you need to investigate the cause.
Show slide 8-15.
Explain QA/QC for active devices.
Up to now, we’ve talked about QA/QC for passive devices.
If you use an active radon device to measure radon, you should have it calibrated at least once a year to make sure it is operating correctly. Check the manual that came with your device or ask the manufacturer to refer you to a calibration lab.
Show slide 8-16.
Explain.
Like your car and your teeth, your instruments need periodic checkups to make sure that they are working correctly.
Check that all components are in good working order:
• Batteries
• Pumps
• Electronics
• Airflow
Show slide 8-17.
Explain.
A QA/QC plan includes not only the measurements and calibration we have discussed, but also a system to document all of your measurements. In the previous lesson, we discussed the need to document
• Information about the device
• Times
• Exact location of device
• Other building information
• Any other test conditions
Show slide 8-18. Click to animate.
Explain.
.
In addition, you need to document your QA/QC actions.
Include the standard information, but be sure also to note
• For passive devices
o Percentage of QA/QC tests in relation to the total number of tests conducted
o The label you used to identify the test as a QA/QC measurement, rather than an ordinary measurement
o The type of QA/QC test you used
• For active devices
o Calibration dates and any other details of the calibration process
In addition, you can request a copy of the QA/QC plan from any lab whose services you use.
Show slide 8-19.
Explain limits of information quality.
I should mention that despite your best efforts, there are limits on the quality of information you can obtain.
The test is out of your control when it is left unattended. You have to do your best to inform residents and persuade them to maintain test conditions and not to interfere with the test.
Show slide 8-20.
Distribute handout 8-1.
Summarize the lesson.
In this lesson, we talked about quality control and quality assurance to reduce or eliminate errors in radon measurement and make sure that all measurements meet EPA quality standards.
We talked about measuring to assess precision and accuracy.
For passive devices, we identified three types of tests:
• Duplicates to measure precision
• Spikes to measure accuracy
• Blanks to measure accuracy by determining bias
We noted that
• At least 10% of all measurements should be duplicates
• At least 3% of all measurements should be spikes
• At least 5% of all measurements should be blanks
Show slide 8-21.
Explain.
We explained that active devices must be calibrated at least once a year.
Show slide 8-22.
Explain.
We explained that QA/QC for all types of devices also includes
• Routine instrument checks
• Documentation of all measurements
• Documentation of all QA/QC activities
Show slide 8-23.
Ask.
Do you have any questions about QA/QC?
Show slide 8-23.
Lesson 8-7
Measuring radon in residential properties How can you provide QA/QC?
Check comprehension. Distribute handout 8-2A.
Learners may answer the questions individually, in pairs, or in small groups. This comprehension check is not graded.
Now you’re going to see whether you remember the main points that we’ve discussed in this lesson. Please answer the questions on handout 8-2A. When you all finish, we’ll review the answers together.
Review the answers. Distribute handout 8-2B, the answer key.
Resources
Sullivan, Allison P. 2006. “Radon Testing in Connecticut Schools.” Connecticut Department of Public Health, Radon Program. Presentation. July 26.
U.S. Environmental Protection Agency. 1992. Indoor Radon and Radon Decay Product Measurement Device Protocols (EPA Publication No: 402-R-92-004; July 1992). www.epa.gov/radon/pubs/devprot1.html
------. 1993. Protocols for Radon and Radon Decay Product Measurements in Homes (EPA publication No: 402-R-93-003; May 1993). www.epa.gov/iaq/radon/pubs/homes_protocols.pdf
Lesson 8-7
Measuring radon in residential properties How can you reduce radon in a home?
Handout 8-1: QA/QC lesson summary
Importance of measuring to assess precision and accuracy
• Provide reliable information for clients to make decisions affecting health and finances
• Meet EPA quality standards
For passive devices
Type of test / Measures / How it works / % of total measurements /Duplicate / Precision / • Send two identical devices, exposed the same, to lab
• Average the two results
• Calculate relative percent difference
RPD = (Result 1 – Result 2) x 100
Average of two results
RPD should be no more than 25% / At least
10%
Spike / Accuracy / • Send unexposed device to QA/QC lab where it will be exposed to known radon concentration
• Send exposed device to analytical lab
• Calculate the value
Target value – Measured value
Target value
Calculated value should be no more than 0.10 / At least
3%
Blank / Bias/accuracy / • Send unexposed device to lab
Result should be
0 pCi/L or lower limit that device can measure / At least
5%
Active devices
Calibrate at least once a year
QA/QC also includes
• Routine instrument checks
• Documentation of all measurements
• Documentation of all QA/QC activities
Lesson 8-7
Measuring radon in residential properties How can you reduce radon in a home?
Handout 8-2A: Check your understanding
Select the best answer from the choices below. Circle the correct answer.
Lesson 8-7
Measuring radon in residential properties How can you reduce radon in a home?
1. A QA/QC program
a. Makes sure that your measurements meet quality standards.
b. Requires that you have a customer service department
c. Is monitored by the EPA
d. Is run by the EPA
2. Match the type of QA/QC test with the feature it measures
a. Blanks / i. Accuracyb. Duplicates / ii. Bias/accuracy
c. Spikes / iii. Precision
3. Match the type of QA/QC test with its associated percentage of total tests.
a. Blanks / i. 3%b. Duplicates / ii. 5%
c. Spikes / iii. 10%
4. To use the duplicate method, you should
a. Conduct two tests, two days apart, using the same passive device
b. Place two passive devices side by side for the same amount of time and send to the same lab
c. Place two active devices side by side for the same amount of time
d. Place two passive devices side by side for the same amount of time and send to two different labs
5. Blanks can be used to
a. Calibrate an active device
b. Find out whether storing an active device has affected the measurements
c. Find out whether storing a passive device has affected the measurements
d. Conduct follow-up testing
6. You should calibrate an active device
a. Once a week
b. Once a month
c. Once a year
d. Once a decade
Lesson 8-7
Measuring radon in residential properties How can you provide QA/QC?
Handout 8-2B: Check your understanding
Answer key
The correct answers are shown in bold.
- A QA/QC program
a. Makes sure that your measurements meet quality standards.
b. Requires that you have a customer service department
c. Is monitored by the EPA
d. Is run by the EPA
- Match the type of QA/QC test with the feature it measures
a. Blanks / ii. Bias/accuracy
b. Duplicates / iii. Precision
c. Spikes / i. Accuracy
- Match the type of QA/QC test with its associated percentage of total tests.
a. Blanks / ii. 5%
b. Duplicates / iii. 10%
c. Spikes / i. 3%
- To use the duplicate method, you should
a. Conduct two tests, two days apart, using the same passive device
b. Place two passive devices side by side for the same amount of time and send to the same lab
c. Place two active devices side by side for the same amount of time
d. Place two passive devices side by side for the same amount of time and send to two different labs