Radon_Reporter_March2020

THE RADON REPORTER | 19 18 | March 2020 SCIENCE AND RESEARCH SCIENCE AND RESEARCH In summary, the Monte Carlo simulation data shown in Table 2 provide a realistic estimate of the confidence level at various sample densities vs. the actual number of units within the complex known to have elevated radon levels. In a real-world situation in which the actual number of units with elevated radon levels is unknown, achieving minimal 90% confidence in every case would require a minimum 90% sample density to ensure that there is no more than one unit in the complex with elevated radon levels. Even at this high a sample density, 1 in 10 surveys would still reach the wrong conclusion. Table 2. Number of successful simulations as a function of sample size. Units > 4 pCi/L 1 2 3 4 5 6 7 8 9 10 10% sampled 10% 19% 27% 35% 41% 47% 53% 58% 62% 66% 25% sampled 25% 44% 58% 69% 76% 82% 87% 90% 93% 95% 33.3% sampled 34% 56% 71% 81% 87% 92% 94% 96% 98% 99% 50% sampled 50% 75% 88% 94% 96% 99% 99% 100% 100% 100% 66.6% sampled 67% 89% 96% 99% 100% 100% 100% 100% 100% 100% 75% sampled 75% 93% 99% 100% 100% 100% 100% 100% 100% 100% 80% sampled 80% 96% 99% 100% 100% 100% 100% 100% 100% 100% 90% sampled 90% 99% 100% 100% 100% 100% 100% 100% 100% 100% 95% sampled 95% 100% 100% 100% 100% 100% 100% 100% 100% 100% • The ANSI-AARST MAMF Standard requires testing 100% of ground floor units. Using the Monte Carlo Method to Evaluate the Reliability of Screening Multifamily Housing for Radon David Wilson, Research Staff, Oak Ridge National Laboratory When screening for radon in a multifamily housing complex using a fixed sample density (e.g., testing 1 in 10 (10%) or 1 in 4 units (25%)), the statistical confidence is dependent upon the assumed elevated radon frequency. For example, testing 25% of units in a complex estimated to have eight units with elevated radon levels will provide 90% confidence. However, if it is assumed that, in the same complex, there are only three units with elevated radon levels, the confidence drops to around 58% for the same sample density. Furthermore, in the previous example, if elevated radon levels are not found during the screening, all that can be stated is that the screening provides 90% confidence that there are no more than seven units in the complex with elevated radon levels. To more fully illustrate this uncertainty, ten separate multifamily housing radon data sets with 1 to 10 units with radon levels ≥4 pCi/L (Table 1) were selected for analysis using the Monte Carlo statistical method. Unlike other mathematically based statistical approaches, the Monte Carlo statistical method relies on repeated analysis of randomly selected data from a 100% sampled complex at various sample densities. Success for each simulation is defined as finding at least one unit with elevated radon levels. In this statistical method, confidence in the overarching conclusion can be greatly enhanced by repeating the simulated screening hundreds or even thousands of times. Table 1. Radon data summary by complex Number of units Building type EPA radon zone Units ≥ 4 pCi/L Average radon level (pCi/L) Standard deviation Highest result (pCi/L) 104 4-plex 3 1 0.6 0.8 4.5 108 6-plex 3 2 0.9 1.1 5.3 144 6-plex 2 3 1.4 0.8 5.3 156 6-plex 2 4 1.4 1.0 7.1 112 8-plex 2 5 1.3 0.9 4.9 112 8-plex 3 6 1.5 1.3 6.2 112 4-plex 2 7 1.5 1.1 6.1 108 4-plex 2 8 1.6 1.2 5.8 120 8-plex 3 9 1.7 1.9 7.8 100 4-plex 1 10 1.4 1.5 7.5 For this study, each of the ten data sets was simulated 1,000 times. For each simulation, the data set was randomized three times before the fixed percentage of data was selected. In cases where the result was a fraction, the number of samples was rounded up to the next whole number. After each individual simulation, the selected data were checked to see if at least one unit had elevated radon levels. If that was the case, the simulation was counted as a success. The simulated process was then repeated ten additional times. The average of all ten times—1,000 simulations—was then calculated and plotted (Table 1). These simulations approximate the findings resulting from screening each complex 1,000 times using randomly selected radon data at a fixed sample density with known units with elevated radon levels. As can be seen in Table 2, 90% confidence can be achieved in multifamily housing neighborhoods at sample densities of ≥25% provided that there are at least eight units in the neighborhood that have radon levels ≥4 pCi/L. However, as the table shows, the confidence decreases as the number of units in the complex with elevated radon levels decreases. For complexes with seven or fewer units with elevated radon levels, correspondingly higher sample densities are required to achieve a similar confidence interval. For example, if only one unit was ≥4 pCi/L, 90% of the units would need to be sampled to achieve the same level of confidence. New AARST Member Benefits are HERE! Your association has been working hard to get you great perks! We changed the look of the Membership Dashboard so you can easily view membership tools: standards, templates, business discounts and more. Did you know AARST has a discount program with Ford vehicles? Look for travel discounts - hotels, resorts, and car rentals (think spring vacation with the family)! Standards (printed copies) bulk discounts up to 70% off for members (no codes needed), and PSA resources for educating your customers. Click the "My Account" button and sign in to your member dashboard. SOLUTIONS radonaway.com MA (800) 767-3703 | IN (800) 523-2084 3” & 4” PVC PIPE CLAMP radon_reporter_quarter_121819.indd 2 2/10/20 11:49 AM