Table 2.

Summary of variables used to model concentrations of HDI, uretidone, biuret, and isocyanurate in the breathing-zone of automotive spray painters

Type	Name	Description	Range of values	Mean value	Median value
Classification	Booth typea	Type of ventilated paint booth	Downdraft, semi-downdraft, crossdraft	NA	NA
Continuous	Airflow	Airflow inside the paint booth (m3 min−1)	0–469	221	238
	Booth volume	Volume of the paint booth (m3)	55.3–684	101	95.2
	Experience	Experience spray painting cars (years)	0.25–40	13.4	12
	Humidity	Average relative humidity (%)	39.0–96.0	72.6	74.0
	Paint concentration (HDI)b	Concentration of HDI in paint (mg l−1)	0.014–1060	280	259
	Paint concentration (uretidone)b	Concentration of uretidone in paint (mg l−1)	0.060–20 900	880	68.2
	Paint concentration (biuret)b	Concentration of biuret in paint (mg l−1)	1.00–23 800	2030	814
	Paint concentration (isocyanurate)b	Concentration of isocyanurate in paint (mg l−1)	0.56–357 000	96 000	94 800
	Paint time	Time spent inside the booth painting (min)	1.0–56.0	8.49	6.50
	Temperature	Estimate temperature during spraying (°C)	23.9–33.9	25.0	23.9
	Total time	Total operating time of the sampling pumps (min)	3.0–105	21.4	17.0
Dichotomous	Enclosure	Type of enclosure surrounding the paint booth	1: curtain, 0: wall	0.063	0
	Gun type	Type of spray gun used for applying paint	1: HVLP, 0: conventional	0.92	1
	Paint type	Type of paint applied to the surface of the vehicle	1: clear coat, 0: other	0.92	1
	Sampler type	Type of sampler used to monitor air concentration	1: two stage, 0: one stage	0.66	1

^aBecause booth type is a character variable use for classification, mean and median values could not be calculated (NA = non-applicable).

^bHDI, uretidone, biuret, and isocyanurate were non-detectable in 3.1, 36, 17, and 1.0% of all paint samples, respectively. Multiple imputation (n = 10 imputed datasets) was used to impute paint-sampling data below detection limits.