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o b � <br /> probability of false negatives is similarly estimated to be at least less than 10%, and less than <br /> 5% in most cases. Inconclusive results should be confirmed by laboratory analysis. <br /> Inconclusive XRF results on accessible, impact, friction or deteriorated sdrfades-should be <br /> regarded as positive for lead unless a subsequent laboratory test proves otherwise. <br /> When paint chip laboratory results are reported in milligrams per square centimeter, a <br /> result greater than or equal to 1.0 is positive for lead. When the results are in percent by <br /> weight, a result greater than or equal to 0.5% is positive for lead. If laboratory results are in <br /> both units, and at least one result is above the 1.0 mg/cm2 or 0.5% standard, then the sample <br /> is positive for lead. <br /> Locations tested by XRF or paint chip sampling may represent other locations. Refer <br /> back to the original inspection to determine the housing components which the samples <br /> represent. Findings of positive, negative, or inconclusive apply to all the components <br /> represented by a sample. <br /> For multi-family housing of 20 or more units where a sample of units has been selected, <br /> grouped the sample results by component type, such as "kitchen walls" or "doors". Each <br /> component type group should consist of at least 40 samples to the extent this is-practical. <br /> Classify XRF results as positive, inconclusive, or negative following the rules above. For any <br /> component type with 20% or more positive results, lead is present at or above the 1.0 mg/sq <br /> on one or more of the components of that type. If all sample results are negative or all sample <br /> results are less than 1.0 mg/cm2, lead is not present at or 1.0 mg/cm2 on any components of <br /> that type. All other cases are inconclusive and require laboratory testing. <br /> To do the laboratory testing, take a paint sample for all XRF sample results that were <br /> greater than or equal to 1.0 mg/cm2. If any of these results are positive, reach the conclusion <br /> that lead is present at or above 1.0 mg/cm2 on at least one component of the type in question. <br /> If no results are positive, reach the conclusion that lead is not present at or above 1.0 mg/cm2 <br /> for any components of that type. Results from the sample can be used to determine which <br /> component types need abatement or control, which do not, and which need further testing in <br /> the unsampled units. <br /> 6 <br />