Page 19 - CleanScience_Fall22
P. 19

Window Sills
     Window Sills Exterior Surfaces Interior Surfaces Attic Surfaces HVAC Returns
40% 39% 14%
9% 4%
2.6 % 5.8 % 1.2 % 1.2 %
0.6 % 0.6 %
1% 0.8% 0%
2% 0% 3%
3%–5% 19% 26%
>5%–10% 18% 13%
>10% 61% 58%
28% 29%
28% 26%
14% 12%
0.7% 0%
29% 27%
                     Table 1. Percentage of similar wildfire smoke residues in the
Sampling Locations
sampling areas impacted by 343 houses.
Table 2. Percentages of samples in each concentration range of char by sampling location for 196 residue- impacted houses.
structures may be expected to have an average char concentration of 􏰁􏰂􏰕2􏰂 for interior samples.
Distance from Wildfire
The distances of the houses from the subject wild􏰊 􏰇re varied from less than a mile to a maximum of 􏰁􏰓􏰋 miles, with 􏰉2􏰂 of the houses located within 3􏰋 miles of the wild􏰇re. The houses closest to the wild􏰇re were impacted by char to a greater extent than those farther from the wild􏰇re. The majority of samples with 􏰁􏰂 or more of char were collected within one mile of the wild􏰇re, as illustrated in Figure 􏰁. The percentage of samples collected at a distance of one mile or less were 63􏰂 and 6􏰒􏰂 for interior locations and 􏰒4􏰂 for attic and exterior surfaces. An additional 􏰉􏰂􏰕􏰁6􏰂 of samples were collected within 􏰁􏰕2 miles, depending on the sample area in Figure 1, with a similar range of percentages collected at 3􏰕􏰓 miles.
Figure 1. Percentage of samples with a char concentration of 1% or more collected within two miles of the wildfire by a similar sampling area.
The average concentration of char generally decreased with distance from the wild􏰇re, as illus􏰊 trated in Table 3. Exterior concentrations were about 2􏰕4 times the average interior concentration for each similar sampling area. An increase in the average char concentration at the greater distances was due to a small number of elevated values for a limited number of total samples.
 The percentages of sampling locations impacted by char􏰀 ash􏰀 or soot concentrations of 􏰁􏰂 or more in the 􏰃􏰄􏰃 ho􏰅ses 􏰆ere listed in Table 􏰁 for each of the 􏰇􏰈e similar sampling areas. Freasor example, char was detected on exterior s􏰅rfaces in 􏰃􏰉􏰂 of the ho􏰅ses and on attic s􏰅rfaces in 􏰉􏰂 of the ho􏰅ses. For interior s􏰅r􏰊 faces, char concentrations of 􏰁􏰂 or more were detected in 􏰄􏰋􏰂 of interior window sill samples b􏰅t in only 􏰁􏰄􏰂 of interior hard surface samples. A char concentration of 􏰁􏰂 or more was detected 􏰌.􏰍 times more fre􏰎uently on interior window sills compared to interior hard sur􏰊 faces, suggesting that interior window sills were a good sampling location for evaluating exposure of the structure to wild􏰇re smo􏰏e residues.
Table 2 describes the percentage of samples in each of the 􏰇ve ranges of char concentrations for four of the 􏰇ve similar sampling areas in this study. The samples were collected in the 􏰁􏰉􏰐 houses in which a char con􏰊 centration of 􏰁􏰂 or more was detected. 􏰑har concentra􏰊 tions on exterior and attic surfaces were concentrated primarily in the higher concentration ranges. About 􏰉􏰒􏰂 of the char concentrations were 􏰃􏰂 or more, and approximately 􏰐􏰋􏰂 of the exterior and attic samples had a char concentration exceeding 􏰁􏰋􏰂.
Char concentrations in the interior window sill and hard surface samples were concentrated at the lower char concentrations, with a secondary grouping at the highest concentration. About 􏰓􏰓􏰂 of the interior surface samples had a char concentration of 􏰁􏰂􏰕2􏰂, and about 2􏰍􏰂 had a char concentration exceeding 􏰁􏰋􏰂. 􏰖hile 􏰉􏰒􏰂 of the char concentrations were 􏰃􏰂 or more in the exterior and attic samples, about 􏰓􏰓􏰂 of the interior sur􏰊 face samples had a char concentration of less than 􏰃􏰂.
In a previous study of 64 houses by Ward, the char concentrations for wet􏰊wipe samples were less than 􏰁􏰂 in 􏰁4 houses 􏰗22􏰂􏰘, it was 􏰁􏰂􏰕2􏰂 in 􏰃􏰒 houses 􏰗􏰓􏰍􏰂􏰘, 2􏰂􏰕􏰓􏰂 in 􏰁􏰋 houses 􏰗􏰁􏰓􏰂􏰘, and greater that 􏰓􏰂 in three houses 􏰗􏰓􏰂􏰘.3 Both Ward’s study and the
  current study suggest that 􏰓􏰋􏰂 􏰕 6􏰋􏰂 of
FALL 2022

   17   18   19   20   21