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smoke residues. The more surfaces that are sampled, the greater the probability that a surface contaminant may be detected; and the more representative the results will be. Therefore, the sampling plan should ma􏰀imi􏰁e the number of similar sampling areas, and the number of surfaces that can be sampled within each sampling area. However, because of cost limitations, this typically requires a balance between the collection of individual samples and the use of composite samples.
The advantages of collecting individual samples include the ability to perform statistical tests, greater detail in the data, and the ability to detect patterns and gradients in the results. If these factors are important to the sampling plan, then individual samples should be collected. But these advantages may not actually be utili􏰁ed in the typical wild􏰂re inspection. The disad􏰃 vantages are that collecting individual samples either limits the number of surfaces that can be sampled, or requires larger sample si􏰁es to be collected at an increased cost. Collecting composite samples within each similar sampling area is a recogni􏰁ed method for sampling a larger number of surfaces at a reasonable cost. Collecting a composite sample is equivalent to collecting individual samples and then averaging the sample results after they have been analy􏰁ed.3
Extrapolation of Results
The average concentrations of char differed between the similar sampling areas. The concentration mea􏰃 sured for one sampling area was not a reliable predictor of the concentration for another sampling area. For example, sampling the interior window sill of a house did not provide very much information as to what the sample result would be for the interior hard surfaces. Char was not detected on the exterior surfaces of 61 houses in which char was detected on interior window sills. In these 61 houses, a char concentration of 1􏰄 was detected on 􏰅6 window sills; 􏰅􏰄 char on 1􏰆; and 3􏰄􏰇3􏰈􏰄 on 1􏰈 window sills.
The lack of association between the detection of char on interior window sills and interior hard surfaces was described in Table 􏰉. 􏰊 char concentration of 1􏰄 or more was detected on both interior window sills and interior hard surfaces in 143 houses. For example, 43 of the paired char concentrations only differed by 1􏰄. However, the paired char concentrations on inte􏰃 rior window sills and hard surfaces differed by 3􏰄 or more in 63 of the 143 houses, and the differences in the paired char concentrations in 16 of the houses ranged from 􏰅􏰉􏰄􏰇􏰌􏰈􏰄.
These results were consistent with a previous study in which char concentrations were compared on interior window sills and interior hard surfaces for 18 wet􏰃wipe samples in 48 houses.2 In that study, 4􏰉􏰄 of the properties that had been impacted by wild􏰂re smoke residues had substantially different average char concentrations in these two sampling area.
1% 43 30%
2% 37 26%
3% 4 3%
5% 19 13%
10% 14 10%
15% 10 7%
25% – 90% 16 11%
Table 5. Percentage of houses with the indicated difference in char concentrations between the interior window sill and interior hard surface samples in 143 houses.
The results in Table 5 suggested differences in char concentrations between interior window sills and interior hard surfaces may be common. Since these two locations may be used to evaluate the impact of wild􏰂re smoke residues, the results suggested caution should be used when extrapolating char concentrations between sampling areas to evaluate impact.
The differences in char concentrations were compared for a broader selection of sampling areas in Table 6. The coef􏰂cients of correlation 􏰍r􏰃value􏰎 for the differences in char concentrations were calculated for the four pairs of similar sampling areas in Table 6. The low correla􏰃 tions between the four sampling areas, with three of the four r􏰃values essentially 􏰈.2, reinforced the conclusion that char concentrations from one sampling area should be used with caution to estimate char concentrations for other sampling areas.8
          LOCATION 1
  Window Sills
Window Sills
Window Sills
Attic Surfaces
Hard Surfaces 0.23
Attic Surfaces 0.17
Exterior Surfaces 0.37
Exterior Surfaces 0.21
    22 | The Cleaning Industry Research Institute
FALL 2022
Table 6. Coefficients of Correlation between the char con- centrations were measured for similar sampling areas.
􏰏 The wet􏰃wipe sampling method was an effective method for sampling wild􏰂re smoke residues, especially char. The method could be applied to both smooth and intricate hard surfaces, as well as

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