Table 3 Ordered relative irritancy scale for 22 VOCs measured in the Calif. Healthy Building Study. The RD50 for each VOC was referenced to the RD50 for toluene. Compound Chemical Class Relative Irritancy Referenced to Toluene Styrene Aromatic 7.9 Ethyl acetate Ester 7.6 Butyl acetate Ester 6.2 1,2,3-Trimethylbenzene Aromatic 4.1 Hexanal Aldehyde 4.0 Pentanal Aldehyde 3.9 1,2,4-Trimethylbenzene Aromatic 3.6 m/p-Xylene Aromatic 3.4 1,3,5-Trimethylbenzene Aromatic 3.16 2-Ethyltoluene Aromatic 3.15 o-Xylene Aromatic 3.08 3/4-Ethyltoluene Aromatic 2.9 Ethylbenzene Aromatic 1.7 2-Butoxyethanol Alcohol 1.6 Toluene Aromatic 1.0 Benzene Aromatic 0.46 2-Propanol Alcohol 0.40 n-Heptane Alkane 0.26 n-Octane Alkane 0.25 Ethanol Alcohol 0.17 2-Propanone (acetone) Ketone 0.09 n-Nonane Alkane 0.07