Topic 4 - Audio 46 Key Points : Measures taken to increase confidence in results. Quality Assurance: Program that assures that measures are being done and in a timely manner. Precision: How close measurements agree with each other. Determined by how close measurements are to each other (Duplicates). You won t know the actual radon value of a home, but you can compare how close results of duplicate devices agree. Bias: Is there something that is causing results to be consistently different? Determined by analyzing devices that have not been exposed (Blanks) If results of unexposed devices show radon, there may be a bias. Accuracy: How close and consistent results are to target value? Determined by exposing devices to known radon or radon decay product concentrations (Spikes) Sensitivity: The ability to detect low levels with good precision and minimal bias. Is a function of the device used Often expressed by the devices lower level of detection or counting efficiency Who needs a quality control plan? People analyzing their own devices Laboratories People utilizing devices analyzed by laboratories Everyone who provides measurement services! 1
Topic 4 - Audio 47 Duplicate alpha track detectors Key Points - Duplicates (10%) Duplicate charcoal devices Side-by-side, simultaneously deployed devices - 4-inches apart Frequency: 1 duplicate every 10 th test (10%), maximum of 50 per month Conduct routinely rather than all at once. Conduct duplicate testing for each type of device you use. Send to lab as though they were normal devices. Do not alert lab that they are duplicates Obtain results and calculate relative percent difference (RPD) Difference between measurement results divided by their average Construct Control Charts (see below) Plot RPDs on Control Charts One for averages equal to or greater than 4pCi/L or 0.02WL One for averages less than 4pCi/L or 0.02WL Look for trends See Appendix B of EPA s, Protocols for Radon & Radon Decay Product Measurements in Homes, June 1993 Duplicates 4 pci/l Duplicates < 4 pci/l 36% RPD 28% Control Limit 1% Warning Level 5% 67% 50% Control Limit 1% Warning Level 5% 14% In Control Level Expected 25% In Control Level Expected Dates: 4/28/97 5/14/97 5/17/97 5/22/97 6/05/97 6/15/97 7/10/97 7/29/97 8/03/97 4/30/97 5/12/97 5/15/97 5/20/97 6/08/97 6/14/97 7/13/97 7/22/97 8/01/97 No more than 1% of your duplicates should exceed the Control Limit 2
Topic 4 - Audio 48 Key Points - Field Blanks (5%) Blank and regular Electret ion chamber Unexposed Devices - Deploy in field along side regular test device Helps pick up problems with storage and during transportation Frequency: 1 blank every 20 th test (5%) maximum of 25 per month Conduct routinely rather than all at once. Conduct blank testing for each type of device you use. Send to lab as though they were normal devices. Do not alert lab that they are blanks Open and immediately close -provide dates and times consistent with normal deployment. Construct Control Chart Place results on chart and look for trends Results should be at lower level of detection for device (close to zero) What can cause bias? Poor storage practice Documentation errors Problems with the lab Need for calibration of device detection equipment. 8 Blank Result 6 4 2 0 11/15/2004 11/29/2004 12/13/2004 12/27/2004 1/10/2005 1/24/2005 2/7/2005 2/21/2005 3/7/2005 3/21/2005 4/4/2005 4/18/2005 Date Plot shows bias increase 3
Topic 4 - Audio 49 Key Points - Blind Spiking (3%) Devices sent to chamber for exposure Radon or radon decay products levels are carefully measured and controlled in chamber. Frequency: Three (3) spikes for every 100 measurements Minimum 3 per year, maximum 6 per month Procedure: Send to chamber for exposure Send to laboratory for analysis Do not alert lab to fact they are spikes Compare result from lab to level device was exposed. Calculate Relative Percent Error (Lab value chamber value) x 100 Chamber Value Place on Control Chart Look for trends What could cause a big difference? Improper storage or handling Laboratory errors Contact laboratory to discuss discrepancies as that helps them too 30.00% Accuracy of Spikes 20.00% 10.00% 0.00% -10.00% -20.00% 1/18/2005 6/10/2005 8/10/2005 Plot Relative percent Error on chart and look for trends. Values should be within 25% -30.00% 4
Topic 4 - Audio 50 Key Points Continuous monitors undergoing Analytical Devices: calibration in small chamber Devices that actually detect the measured variable Calibration: Frequency: once every year Each device is to be calibrated Manufacturers and chambers provide this service Exposed to known environment and reporting formula adjusted accordingly. If device has air pump, the air flow measurement device is also to be calibrated. Background Checks: Devices either have or accumulate radioactivity Device exposed to nitrogen (i.e. no radon or radon decay product) and offset from zero determined. Background value entered into formula for future result calculation. Best done by manufacturer or chamber at time of calibration. Criteria: Any device that actually measures variable needs to be calibrated. If you own more than one device, each one needs to be individually calibrated. Examples: Continuous radon monitors Continuous radon decay product monitors Counters for activated charcoal devices Electret voltage readers 5
Topic 4 - Audio 51 Key Points - Field QA/QC for Analytical Devices Examples: Continuous radon or radon decay product monitors Electret readers Grab sample devices (diagnostic tools) Source Checks Some devices can be checked with a radioactive source, like Thorium 230, which releases a relatively constant amount of alpha particles. Some devices have a built-in pulse generator that can simulate ionization. Should be done before each measurement, to verify counter efficiency. Duplicates If like devices are available, place side-by-side every 10 th measurement (10% duplicates). If like devices are not available, place another device that measures that same variable (radon or radon decay products) side-by-side every 10 th measurement (10% duplicates). Background Devices that pump air into a scintillation cell which could become contaminated are to have a background check every 1,000 hours of operation. Exposed to aged air or nitrogen Good idea for other continuous monitors to expose to a low radon environment (e.g., in your car) Cross-Checks Informal comparison of device with another recently calibrated device Frequency: once every 6-months Note: radioactive source checks replace the need for this requirement. Routine checks Air flow, if applicable Batteries Data logger,etc. 6
Topic 4 - Audio 52 Key Points Performance Tests Who must pass performance test? Individuals or firms actually producing the reported value. Laboratories Users of field analytical devices that produce measurement. Exemption: Blind monitors Where raw data from field deployed monitor is sent to a central lab who generates report and interprets the results. Central lab must pass performance test. Frequency: Prior to being listed as proficient for a given device Depending upon certification requirements (typically with renewal every two-years) Procedure: Make arrangements with certified chamber recognized by your credentialing agency. Send monitor with your instructions Monitor will be exposed at chamber and returned to you. Calculate results and send result to chamber If within 25% of chamber value, a performance test Pass letter will be issued. Send letter to your credentialing agency as proof of passage. Other: To be conducted for each different analytical device type you want to be listed for. If you own more than one of the same device type, you only need to submit one of the devices. This is different from calibration. If passive devices, five devices are to be submitted and each one within 25% of chamber value. Only approved devices can be submitted for performance tests EPA approved Certification board approval (NRSB or NRPP) 7
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