Table 6.

Estimation of RD and potential confounding exposures

Agenta	Location	Measurementsb [type: n; range of AMs by facility (years)]	Description of estimates and levels assigned	% of cohort potentially exposed to detectable levels
Respirable dust	UG	Pc: n = 273; 1.2–6.1 mg m−3 (1970s–1990s)	Facility and decade specific. Three categories based on where workers spent most of their time underground. Range is for the eight facilities across all decades: production and crusher, 1.2–3.8 mg m−3; haulage and travel ways, 0.9–5.1 mg m−3; and shop and office, 0.4–0.5 mg m−3	100
	S	P: n = 169; <0.1–1.4 mg m−3 (1970s–1990s)	Facility and decade specific. Three categories based on the type of surface worker. Range is for the eight facilities across all decades: Crushing and screening, 0.9–3.4 mg m−3; other production and loading, 0.5–1.1 mg m−3; and maintenance and support, 0.3–0.6 mg m−3
Silica	UG and S	A: n = 217; <0.01–0.02 mg m−3 (95% NDd) (1998–2001)	Categorical score, based on the AMs of area silica measurements, by facility: 3—sandblasters (all facilities): not based on measurements; 2—all UG jobs and all surface production jobs likely exposed to the ore at Facilities G, H, and I: 0.02 mg m−3; 1—all UG jobs and all surface production jobs likely exposed to the ore at Facilities B, D, and J: 0.01 mg m−3; and 0—all jobs at Facilities A and E and remaining surface jobs at Facilities B, D, G–J: <0.01 mg m−3	80
		P: n = 441; 0.01–0.02 mg m−3 (85% NDd) (1970s–1990s)
Radon	UG	A: n = 28; (100% ND)e (1998–2001)	Based on the AMs of the radon measurements: UG workers at Facilities A, B, D, E, and G: 0.02 WL; UG workers at Facilities H–J: 0.01 WL;	67
		A: n = 251; 0.01–0.02 WL (54% ND) (1970s–1990s)
	S	No measurements	0—All surface jobs
Asbestosf	UG and S	P: n = 11; all <0.1 fiber per cc (1980s)	Categorical scores, based on an evaluation of sources: 3—pipe fitters; 2—auto and diesel mechanics, boiler ops, power ops, and bricklayers; 1—dryer ops, kiln ops, maintenance workers, and mechanics; and 0—all other jobs	40
		Bulk samples: n = 15; (100% ND) (1998–2001)
PAHs, as benzo(a)pyreneg	UG and S	No PAH measurements on non-diesel sources	Categorical scores, based on an evaluation of the job's potential contact with PAH sources other than diesel equipment: 1—mechanics, powerhouse ops, blacksmiths, boiler ops, welders, kiln ops, dryer ops, firemen, maintenance workers, ironworkers, pipe fitters, and steelworkers; 0—all other jobs	41

A, area measurement; n, Number of measurements; ND, not detected; Ops, operators; P, personal measurement; S, surface; UG, underground; WL, working level.

^aAgent: few measurements were available for arsenic, cadmium, and nickel and therefore they were not assessed. Measurements were generally nondetectable in 1998–2001 (97, 87, and 88%, respectively) and 1970s–1990s (80, 92, and 51%, respectively).

^b1998–2001 indicates measurement results from the DEMS surveys.

^cNo personal RD measurements taken in the DEMS surveys.

^dThe LOD for the DEMS silica data was 0.005 mg m⁻³. The LOD used for the MIDAS silica data was the lowest detectable value (0.01 mg m⁻³). All values <LOD were imputed by (Hornung and Reed, 1990).

^eThe LOD for the DEMS radon data ranged from <0.01–0.07 WL across the facilities. The LOD used for the MIDAS radon data was the lowest detectable value (0.01 WL). All values <LOD were imputed by (Hornung and Reed, 1990).

^fThe LOD for asbestos bulk samples is <1% asbestos (http://www.cdc.gov/niosh/nmam/pdfs/9002.pdf). Asbestos measurements are presented for information purposes only, as they were not used to categorize workers' exposure.

^gPAHs were evaluated for sources other than diesel equipment.