Page 20 - CleanScience_Fall22

Miles
Exteriors
Attics
Window Sills
Interior Surfaces
1
2
3–5
6 – 150
12.8% 3.6% 3.0% 3.6% 6.1%
unprotected surfaces that were subject to losses due to wind and weather, 􏰓􏰔 radiation, physical degradation, and physical removal. However, the decrease in char concentration on interior window sills was similar to the rate on exterior surfaces. The interior window sills may have been disturbed less frequently than interior hard surfaces, and were protected from weathering effects. This similarity in rates suggests physical degradation may have been primarily responsible for the loss of char during this period of time.
This result could lead to the false conclusion that since the visible char particles 􏰕disappear􏰖 over time, cleaning and restoration are not required. However, conservation of mass should be expected. Presumably, the larger char particles degrade into smaller particles over time, which would be expected to be in the inhal􏰌 able and respirable si􏰗e ranges 􏰍1–10 microns􏰎􏰘 expo􏰌 sure to the lower respiratory tract would likely increase as the char particles physically degrade. Since char consists of both elemental and organic carbon, besides the effects of PM2.5 and PM10, it can also contain irri􏰌 tant and carcinogenic compounds.4, 5, 6 Therefore, this scenario suggests that cleaning and restoration should occur as soon as possible after the wild􏰃re.
Cleaning and Restoration
The primary objectives of sampling and evaluating wild􏰃re smoke residues are to 1􏰎 identify those structures that have been impacted by the residues, and 2) determine a scope of work for the cleaning and restoration of the impacted properties. The characteri􏰗ation of char concentrations in this study was based on a relatively large sample of 343 houses. 􏰏 previous study of 4􏰐 houses compared replicate wet􏰌 wipe and tape􏰌lift samples for interior window sills and interior hard surfaces􏰚sampling areas that were also
2
included in the current study. When the results of these
two studies are considered together, several factors that can affect the clean􏰛restore decision can be evaluated. These factors include the primary wild􏰃re smoke residue, the concentration of a wild􏰃re smoke residue that indicates a structure has been impacted and should be subject to cleaning􏰛restoration, and the impact of the sampling method on the clean􏰛restore decision.
There are no consensus guidelines for the concentrations of wild􏰃re smoke residues that can be used to identify houses that have been impacted by those residues.1 However, the selection of the concentration of a smoke residue as a minimum criterion for assessing impact determines which structures may be de􏰃ned as having been impacted by wild􏰃re smoke residues, and
26.5% 19.9% 10.6%
20.0% 24.0% 5.4% 8.0%
9.2% 7.5% 2.9%
11.0%
Table 3. Average percent char by distance from the wildfire and by similar sampling area for 343 samples.
Peak char concentrations on exterior surfaces tended to decrease 􏰀ith distance fro􏰁 the 􏰀i􏰂d􏰃re in the range of 1–30 miles. Peak char concentrations were o􏰄er 􏰅0􏰆 at 1–􏰇 miles􏰈 􏰉0􏰆 at 􏰊 miles􏰈 and 􏰇0􏰆 at 30 miles. However, average char concentrations at various distances were in a relatively narrow range and were poorly correlated with distance. Peak char concentrations on interior window sills also decreased with distance. The range of char concentrations for interior window sill samples varied from a low of 1􏰆 to a high of a􏰋out 3􏰊􏰆.
Elapsed Time Since Wildfire
Changes in the initial conditions can occur as the elapsed time 􏰋etween the wild􏰃re and the inspection increases, making it more dif􏰃cult to evaluate the ini􏰌 tial impact of wild􏰃re smoke residues. The elapsed time 􏰋etween the wild􏰃re and the date of the inspection varied from a minimum of nine days to a maximum of 1,􏰇􏰅0 days 􏰍3.􏰊 years􏰎. 􏰏􏰋out 􏰅􏰅􏰆 of the inspections occurred within the 􏰃rst 1􏰐0 days, with 1􏰑􏰆 of inspec􏰌 tions occurring within 30 days, 􏰇􏰒􏰆 within 30–􏰒0 days, and 3􏰇􏰆 within 􏰒0–1􏰐0 days.
The average char concentration decreased on exterior surfaces, interior window sills, and interior hard surfaces during the 􏰃rst ten months. The rates at which the aver􏰌 age char concentration decreased per 30􏰌day period were 1.􏰅􏰆 on interior hard surfaces, 1.3􏰆 on exterior sur􏰌 faces, and 1.1􏰆 on interior window sills. 􏰏lthough these rates were variable and should be viewed as approxi􏰌 mations, they provided an order􏰌of􏰌magnitude estimate for the removal rates for surface char. The results sug􏰌 gested that the elapsed time between the wild􏰃re and the inspection should be considered as a potentially biasing factor when estimating initial conditions.
The loss of char over time may have been due to several factors. The average concentration of char decreased at the highest rate on interior hard surfaces. Hard surfaces were presumably subject to frequent occupant activities such as cleaning and disturbance, as well as increased physical degradation due to contact. The exterior samples were collected from
20 | The Cleaning Industry Research Institute
FALL 2022