Graphical illustration of the perception of eye irritation during exposure to filtered air, unfiltered diesel exhaust, and diesel exhaust filtered with Filter A and B, respectively. The symptom score is presented both pre- and post-exposure according to a modified Borg scale. A shift toward the right indicates increased symptoms during exposure. Each individual is represented by one data point. Where data from several subjects are clustered, the number (n) of subjects is indicated. Wilcoxon’s Signed-Rank test was used for comparison of absolute delta values (Max symptom score minus before exposure) across exposure to unfiltered DE and filter air, unfiltered DE and DE filtered with filter A and unfiltered DE with DE filtered with filter B (active charcoal containing filter). Data were considered significant at p < 0.05. Significant differences between air and unfiltered diesel exhaust, and diesel exhaust filtered with filter A (particle filter) and B (particle and active charcoal filter) are given in the figure. DE with filter B gave significantly less symptom than filter A.