Table 1.

Estimated exposure concentrations of respirable free silica by time period

Job class	Location	<1940		1940–1949*	≥1950
		N	mg/m3	mg/m3	N	mg/m3
Bit grinder†	Quarry	1	0.17
Blacksmith†	Quarry	4	0.03
Boxer	Shed	14	0.08	0.06	103	0.04
Carver	Shed	19	0.37	0.22	149	0.07
Channel bar	Quarry	3	0.15	0.08		0.01‡
Crane	Shed	9	0.16	0.11	32	0.05
Cutter	Shed	331	0.39	0.23	1569	0.07
Draftsman	Shed	12	0.01	0.01		0.01
Driller	Quarry	120	1.07	0.54	7	0.01
Foreman	Shed		0.12	0.09	9	0.05
Grinder	Shed	31	0.19	0.13	5	0.07
Jackhammer	Quarry	10	1.05	0.56	7	0.06
Labourer	Shed		0.24	0.17	8	0.10
Lumper	Shed	5	0.30	0.18	138	0.06
Maintenance	Shed	12	0.24	0.16	28	0.07
Quarry (general)	Quarry	22	0.13	0.07		0.01‡
Office worker	Shed	29	0.04	0.04		0.04
Polisher	Shed	35	0.12	0.10	570	0.07
Sandblaster	Shed	43	0.24	0.16	337	0.07
Sawyer	Shed	13	0.13	0.10	634	0.06
Shed (general)	Shed	153	0.12	0.09	491	0.05
Surfacer	Shed	150	0.28	0.18	101	0.08

^*Estimates are averages of those for the earlier and later periods because few measurements were available from 1940 to 1949.

^†Job not performed after 1939.

^‡Trend applied using jackhammer and driller data.