. 2016 Feb 9;33(3):193–210. doi: 10.1177/0748233715619072

Table 4.

Task benzene air concentrations by task bin and area.

Task Bin (percent of total)^a	Description of task	Status	Area(s)	n	Detection frequency (%)	Benzene Concentration (ppm)
Task Bin (percent of total)^a	Description of task	Status	Area(s)	n	Detection frequency (%)	Mean	Standard deviation	Geometric mean	Geometric standard deviation	75th percentile	95th percentile	Minimum detected	Maximum detected
Blinding and breaking (31%)	Installing blinds, breaking lines or opening equipment (including coke drums) and installing or removing equipment that has typically been drained	All	Reformer	576	58%	2.7	8.6	0.18	16	1.5	13	0.018	107
		All	Tank farm	20	65%	14	30	0.73	21	2.2	80	0.73	105
		All	All other areas	572	24%	0.53	2.7	ND	ND	ND	1.8	0.020	39
Blinding and breaking-undrained (1%)	Installing blinds, breaking lines or opening equipment and installing or removing equipment confirmed to not have been drained prior to line break	All	All areas	53	47%	0.52	0.96	0.06	14	0.53	2.5	0.032	4.71
Sample collection (20%)	Collecting process sample from line/unit	All	All areas	770	28%	0.51	2.3	ND	ND	0.15	2.6	0.010	47
Equipment cleaning and repair (13%)	Maintaining or repairing units/equipment, calibrating equipment or meters, changing or cleaning filters and screens, and cleaning equipment	All	All areas	483	36%	1.1	6.0	ND	ND	0.20	4.2	0.0060	100
Sample analysis (10%)	Laboratory analysis of samples including washing of glassware, pouring of samples, disposing of samples, and other laboratory work	All	All areas	387	44%	1.0	4.4	ND	ND	0.38	4.0	0.025	58
Gauging (8%)	Gauging tanks to determine liquid levels	All	All areas	284	11%	0.16	0.95	ND	ND	ND	0.37	0.014	12
	All assigned tasks^b	All	All areas	3768	35%	1.1	5.5	0.051	12	0.26	3.6	0.0060	107
		1976-1989	All areas	1615	53%	1.9	7.6	0.40	3.0	0.78	8.4	0.00011	107
		1990-2006	All areas	2141	22%	0.40	3.0	0.22	2.4	0.090	1.4	0.000055	100

^aTotal percentage for tasks shown is 83%.

^bTotal includes all short term samples except where task bin could not be assigned (n = 588). Year of sample collection unknown for 12 samples. ND: Geometric mean and geometric standard deviation not calculated because more than 50% of the samples were below the limit of detection. Percentile not calculated because the proportion of results below the detection limit exceeds the selected percentile.