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HEURESIS PCS December 2015 Determine if the XRF testing in the units or house passed or failed the test by applying the steps below. Compute the Retest Tolerance Limit by the following steps: Determine XRF results for the original and retest XRF readings. Do not correct the original or retest results for substrate bias. In single-family and multi-family housing, a result is defined as a single reading. Therefore, there will be ten original and ten retest XRF results for each house or for the two selected units. Calculate the average of the original XRF result and the retest XRF result for each testing combination. Square the average for each testing combination. Add the ten squared averages together. Call this quantity C. Multiply the number C by 0.0072. Call this quantity D. Add the number 0.032 to D. Call this quantity E. Take the square root of E. Call this quantity F. Multiply F by 1.645. The result is the Retest Tolerance Limit. Compute the average of all ten original XRF readings. Compute the average of all ten re-test XRF readings. Find the absolute difference of the two averages. If the difference is less than the Retest Tolerance Limit, the inspection has passed the retest. If the difference of the overall averages equals or exceeds the Retest Tolerance Limit, this procedure should be repeated with ten new testing combinations. If the difference of the overall averages is equal to or greater than the Retest Tolerance Limit a second time,then the inspection should be considered deficient. Use of this procedure is estimated to produce a spurious result approximately 1% of the time. That is, results of this procedure will call for further examination when no examination is warranted in approximately 1 out of 100 dwelling units tested. TESTING TIMES: In the Action Level paint test mode, the instrument takes the longest time to complete readings close to the Federal standard of 1.0 mg/cm'. The table below shows the mean and standard deviation of actual reading times by reading level for paint samples during the November 2015 archive testing. The tested instruments reported readings to one decimal place. No significant differences in reading times by substrate were observed. These times apply only to instruments with the same source strength as those tested (2.0 mCi). Instruments with stronger sources will have shorter reading times and those with weaker sources, longer reading times, than those in the table. Mean and Standard Deviation of Reading Times in Action Level Mode by Reading Level Reading (mg/cm' Mean Reading Time (seconds) Standard Deviation (seconds) < 0.7 3.48 0.47 0.7 7.29 1.92 0.8 13.95 1.78 0.9— 1.2 15.25 0.66 1.3 — 1.4 6.08 2.50 > 1.5 3.32 0.05 Page 3 of 4