In order to assess fluid penetration into tufted carpets, this study developed a new method for determining porosity and pore size distribution in tufted carpets, so as to facilitate the accurate analysis of bloodstains on carpet.
Bloodstains and bloodstain patterns are often observed at crime scenes, and their analysis through bloodstain pattern analysis (BPA) can assist in reconstructing crime scenes; however, most published work related to BPA only deals with hard, non-porous surfaces, and none of the studies have carefully characterized carpets. Soft and porous carpets are often encountered at crime scenes, since they are common in American homes, accounting for 51 percent of the total U.S. flooring market; this has motivated the research described in this article. The study used three kinds of nylon carpet: a low, a medium, and a high face-weight carpet. Each carpet had an anti-stain treatment, which was removed from half of each carpet by steam-cleaning with a pH 12 NaOH solution. This resulted in six carpet samples. Yarn twist, carpet weight, pile height, water contact angles on carpets, water contact angles on individual fibers, and fiber cross-sectional shapes were characterized. Porosity and pore size distribution were analyzed using confocal laser scanning microscopy (CLSM). Porcine blood was used as a human blood substitute at three liquid volumes (30 ìL, 10 ìL, and 2 ìL). Analysis showed that porous carpet construction and anti-stain finishing both affected penetration. The depth of blood penetration decreased with the increase of carpet face-weight, but increased with increased drop height. The removal of anti-stain treatment increased blood penetration into the carpets and changed the pore size distribution. Effects of anti-stain treatment, porosity, and pore size distribution of tufted carpet, as well as blood wicking behaviors on carpets were found to strongly affect blood penetration into the carpets. (publisher abstract modified)