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variability and dispersed obstructing debris particles. Third, it allowed composite samples to be collected, with each composite sample representing the result for 􏰀 􏰂 􏰃 individual surfaces. 􏰄omposite samples increased the probability of detecting wild􏰅re smo􏰆e residues, resulted in a better characteri􏰇ation of the space that was sampled, and reduced sampling cost by allowing more surfaces to be sampled using fewer samples.
􏰈 previous comparison of replicate wet􏰉wipe and tape lift samples indicated that wet􏰉wipe sampling was an effective method for evaluating the impact of wild􏰅re smo􏰆e residues.2 􏰊ne limitation of that study was that both the replicate wet􏰉wipe and tape lift samples were composite samples collected from 􏰀􏰂􏰃 surfaces. Although this is not a recommended practice, the samples were collected as part of a limited add􏰉on research study. Extra care was used to visually inspect both the surface of the tape and the sampled areas after each sample. This was done to check for overloading and to ensure visible debris was picked up by the sticky tape. When the tape visibly approached an overloaded condition, the hygienist was instructed to stop using it. This resulted in the sampling of a range of 􏰀􏰂􏰃 surfaces in each composite sample.
The results indicated there was no difference in the collection, sample preparation, or analytical ef􏰅ciencies between replicate wet􏰉wipe and tape lift samples for interior window sills. 􏰋owever, wet􏰉wipes did perform better on interior hard surfaces. This may have been due to three factors: 1) the advantages of averaging composite samples, 2) the advantages of homogeni􏰇ation during sample preparation by the laboratory as per EPA’s 􏰌AE method 􏰍EPA􏰎􏰏􏰐􏰐􏰎􏰑􏰉􏰒􏰀􏰎11􏰏), and 􏰀) interior hard surfaces varied in contour and roughness compared to smooth, 􏰓at window sills.
A total of 343 houses in northern California that were potentially impacted by one of 22 wild􏰅res were sampled for char, ash, and soot using the wet􏰉 wipe sampling method. The wild􏰅res occurred during a four􏰉year period from 2􏰐1􏰔 through 2􏰐2􏰐. A total of 1,􏰔1􏰃 wet􏰉wipe samples were collected from 􏰅ve hard􏰉surface sampling locations in each house. The 􏰅ve 􏰕similar sampling areas􏰖 included exposed exterior surfaces, attic surfaces, interior window sills, interior hard surfaces, and return plenum surfaces. Field inspections and sample collection were performed by trained, experienced industrial hygienists.
Wet􏰉wipe samples were collected using foil􏰉sealed 􏰗eckton 􏰘ickinson alcohol pads containing 􏰔􏰐􏰙 isopropyl alcohol and measuring 1 􏰚 1 s􏰛uare inch. A pad was used to wipe approximately 8 square inches of the hard surface. The pad was then placed into a clean 4 􏰚 4 square inch 􏰜iplok plastic sample bag, sealed, and labeled. This process was repeated on 3 􏰂 􏰃 hard surfaces inside each property, using a clean pad for each surface. The individual samples were then combined by the laboratory for analysis to provide a composite sample, with the area sampled varying from 24 􏰂 4􏰐 square inches depending on the number of surfaces sampled.
Laboratory Analysis
The wet􏰉wipe samples were shipped to E􏰝􏰞􏰟 􏰟aborato􏰉 ries in Cinnaminson, 􏰠􏰡, typically the day after they were collected, where they were composited and analy􏰇ed. The samples were analy􏰇ed by stereomicroscopy, epi􏰉 re􏰓ected light microscopy, polari􏰇ed light microscopy, TE􏰝􏰎E􏰘􏰢, and 􏰞E􏰝􏰎E􏰘􏰢.2 A minimum wild􏰅re smoke residue concentration of 1􏰙 was de􏰅ned as the 􏰟imit of 􏰣uantitation 􏰍􏰟􏰊􏰣).
The P􏰟􏰝 technique was used for the identi􏰅cation of char and ash, the screening and presumptive analysis of soot clusters, and the reporting of char on a relative area percentage basis using the 􏰌isual Area Estimation 􏰍􏰌AE) method 􏰍EPA􏰎􏰏􏰐􏰐􏰎􏰑􏰉􏰒3􏰎11􏰏). A sample in which a smoke residue was detected at a concentration of 1􏰙 or greater was de􏰅ned as being positive and houses in which positive samples were detected were considered to have been impacted by a wild􏰅re smoke residue.
Detection of Wildfire Smoke Residues
Char was detected at a concentration of 1􏰙 or more in 1􏰒􏰏 􏰍􏰃􏰔􏰙) of the 343 houses, ash was detected at a concentration of 1􏰙 or more in 8.8􏰙 of the houses, and soot was detected in 1.2􏰙 of the houses. Char was detected in 3􏰏3 􏰍21.1􏰙) of the 1,􏰔1􏰃 samples, ash was detected in 3􏰔 􏰍2.2􏰙) of the samples, and soot was detected in four 􏰍􏰐.2􏰙) of the samples.
Char was the primary wild􏰅re smoke residue based on frequency of detection, in this study as well as in two previ􏰉 ous studies. 2, 3 The frequencies of detection for ash and soot in this study were too low for those wild􏰅re smoke residues to be useful for evaluating impact. Since char was the only wild􏰅re smoke residue detected with suf􏰅cient frequency to be useful for evaluating the impact of wild􏰅re smoke residues, evaluations were based on the concentrations of char detected on interior and exterior surfaces.
 Sample Collection
18 | The Cleaning Industry Research Institute
FALL 2022

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