Table 4.

Distribution of underground standardized job titles and exposure-years by underground exposure group^a and by mining facility

Mining facility	Standardized job titlesb (n)	Total E-Yc (n)	Underground exposure group E-Ys (%)d
			U1	U2	U3	U4	U5
A	40	8142	47	49	0	3	1
B	25	5530	51	43	<1	3	2
D	58	11 103	28	63	1	8	1
E	36	3708	46	45	9	0	<1
G	38	5240	68	32	<1	0	<1
H	43	9190	40	53	4	<1	2
I	55	13 236	57	36	4	1	1
J	38	9072	0	0	27	71	2
Total	333	65 220	40	40	6	12	1

E-Y, exposure-years; n, number.

^aDoes not include mixed workers, i.e. workers who worked both underground and on the surface on the same job. For underground jobs, the exposure groups were used only to group the jobs for assigning exposure estimates, in contrast to the surface jobs that had two types of exposure groups.

^bStandardized job titles are the study titles of groups of job entries from the facility's personnel records that differed only in spelling or word order or were synonyms but performed the same tasks.

^cE-Ys is defined as end date minus start date of a job plus 1, divided by 365.2425, and summed across all jobs. E-Ys may not sum to 100% due to rounding.

^dU1 groups were based on the standardized job title; U2 groups comprised groups of standardized job titles that spent similar proportions of time in four major areas of the underground operation; U3 groups were groupings of U2 groups defined by similarity of CO air concentrations; U4 groups were the default, i.e. all underground jobs; and U5 groups were exceptions or overrides. A minimum of five REC measurements from the DEMS surveys was required for assigning the groups, except U5. Assignment was hierarchical from U1 to U5. E-Ys (%), the percentage of E-Ys assigned an exposure estimate based on the identified exposure group.