Page 21 - CleanScience_Fall22

􏰀􏰁􏰂􏰃􏰁 􏰁􏰅􏰆􏰇􏰈􏰇 􏰇􏰁􏰅􏰆􏰉􏰊 􏰋􏰈 􏰇􏰆􏰋􏰌􏰈􏰃􏰍 􏰍􏰅 􏰃􏰉􏰈􏰎􏰏􏰂􏰏􏰐􏰑􏰒􏰈􏰇􏰍􏰅􏰒􏰎􏰍􏰂􏰅􏰏􏰓 􏰔􏰁􏰈 􏰃􏰅􏰏􏰃􏰈􏰏􏰍􏰒􏰎􏰍􏰂􏰅􏰏􏰇 􏰅􏰕 􏰀􏰂􏰉􏰊􏰖􏰒􏰈 􏰇􏰗􏰅􏰘􏰈 􏰒􏰈􏰇􏰂􏰊􏰆􏰈􏰇 􏰆􏰇􏰈􏰊 to assess impact are typically based on professional 􏰌􏰆d􏰐ment 􏰙for e􏰚ample􏰛 􏰜􏰝􏰞 or more􏰟 or 􏰜􏰠􏰞 or more􏰟􏰡􏰓 􏰢sin􏰐 a c􏰁ar concentration of 􏰜􏰝􏰞 or more􏰟 for 􏰀et􏰣 􏰀ipe samples 􏰀as a practical de􏰖nition for assessin􏰐 t􏰁e impact for the 343 houses included in this study.
􏰤 char concentration of 􏰝􏰞 or more 􏰀as consistent 􏰀ith the 􏰥imit of 􏰦uantitation 􏰙􏰥􏰧􏰦􏰡 used by the laboratory to report samples positive for char. In addition, the char concentration 􏰀as less than 􏰝􏰞 in all si􏰚 samplin􏰐 areas in 􏰝4􏰨 􏰙43􏰞􏰡 of the 343 houses. 􏰔􏰀o smaller studies of 􏰩4 and 4􏰪 houses usin􏰐 􏰀et􏰣􏰀ipe samples to collect char found the char concentration 􏰀as less than 􏰝􏰞 in 􏰩3􏰞 and 􏰫􏰫􏰞 of the 􏰀et􏰣􏰀ipe samples, respectively.2, 3 􏰔he avera􏰐e for the three studies 􏰀as 43􏰞, 􏰀hich 􏰀as considered to be a reasonable percentage of houses; therefore 􏰝􏰞 char 􏰀as considered to be a reasonable numerical guideline for evaluating impact.
Both the selection of the sampling method and the minimum residue concentration for evaluating impact can affect the proportion of houses evaluated as requiring cleaning or restoration. For example, the results in Table 2 and in Ward’s study indicated that 􏰬􏰭􏰞􏰮􏰩􏰭􏰞 of char concentrations on interior surfaces may be expected to be 􏰝􏰞􏰣2􏰞. If it 􏰀ere presumed that samples collected from interior surfaces, as compared to the exterior or attic surfaces, would be more relevant for evaluating the impact of wild􏰖re smo􏰘e residues on interior spaces when preparing a restoration work plan, then pre􏰣selecting a minimum residue concentration of 3􏰞 for evaluating impact, for example, would exclude over half of the potentially impacted houses from cleaning or restoration. In comparison, pre􏰣selecting a minimum residue concentration of 􏰝􏰞 for evaluating impact would not exclude any of the potentially impacted houses from cleaning or restoration.
􏰤 previous study of 4􏰪 houses, although limited in si􏰯e, compared the tape lift and wet􏰣wipe methods for collect􏰣 ing char samples from interior window sills and interior hard surfaces.2 Eighteen of the 48 houses included in that study had a char concentration of 􏰝􏰞 or more on the inte􏰣 rior surfaces. These data were used in Table 4 to compare the percentages of those 18 houses that would have been subject to restoration assuming the indicated sampling method and minimum residue concentration of char for assessing impact had been selected in the study.
For example, selecting the wet􏰣wipe sampling method and de􏰖ning a minimum char concentration for assessing impact as 􏰜1􏰞 or more􏰟 would have
identi􏰖ed 1􏰭􏰭􏰞 of the 18 houses as being impacted by wild􏰖re smoke residues. In comparison, selecting the tape lift sampling method and de􏰖ning a minimum char concentration for assessing impact as 􏰜3􏰞 or more􏰟 would have identi􏰖ed 1􏰨􏰞 of the 18 houses as being impacted by wild􏰖re smoke residues.
Minimum Char
Wet Wipe
Tape Lift
Difference
1% or More
3% or More
Difference
100% 94% 6%
72% 17% 76%
28% 82% NA
FALL 2022
THE JOURNAL OF CLEANING SCIENCE | 21
Table 4. Effect of sampling method and minimum char concentration for evaluating impact on the percentages of 18 houses subject to restoration.
The percentages of the 18 houses in Table 4 illustrate the effects of selecting a sampling method and minimum char concentration for assessing the impact on the decision to clean􏰑restore a structure. Table 4 suggests that these two parameters can have meaningful effects on whether or not a structure will be evaluated as having been impacted by wild􏰖re smoke residues and subject to cleaning and restoration.
The largest difference in the evaluation of impact in Table 4 occurred between using 1􏰞 or 3􏰞 as the minimum char concentration for evaluating impact. There was only a 􏰩􏰞 difference in the evaluation of impact between the wet􏰣wipe and tape lift sampling methods when a char concentration of 1􏰞 or more was used to assess impact. However, this difference increased to 􏰨􏰩􏰞 when the criterion used to evaluate impact was changed to 3􏰞 or more.
Composite Samples
The wet􏰣wipe sampling method allowed composite samples to be collected, with each composite sample representing the result for 3 – 5 individual surfaces.7 Using composites to sample multiple surfaces increased the probability of detecting wild􏰖re smoke residues, better characteri􏰯ed the spaces that were sampled, and reduced costs. However, composite samples should only be collected within a single “similar sampling area.􏰟 I.e., all individual samples in a composite sample should be collected from interior window sills, interior hard surfaces, etc.
Char was only detected in one of the six similar sampling areas in 􏰰􏰩 􏰙4􏰰􏰞􏰡 of the 1􏰰􏰩 houses in which a char concentration of 1􏰞 or more was detected, and that one sample represented 3–5 surfaces. This result emphasi􏰯ed the need to sample as many surfaces as possible in order to detect the presence of wild􏰖re