Table 5.

Comparisons between thoracic and respirable fraction by decade, industry, operation and fluid types

Classification		Thoracic			Respirable
		No. of measurements	WAM (mg m−3)	SD (mg m−3)	No. of measurements	WAM (mg m−3)	SD (mg m−3)
Decade	1980s				131	0.32	0.10
	1990s	1968	0.48	0.21	102	0.33	0.43
	2000s	4663	0.40	0.15	37	0.27	NA
	P-value		0.063			NS
Industry type	Auto	4788	0.46	0.18	233	0.32	0.29
	Auto part	439	0.35	0.07	37	0.27	NA
	Small-jobs	1384	0.32	0.07
	P-value		0.007			NS
Operation type	Grinding	231	0.48	0.19	36	0.22	0.04
	Machininga	5805	0.43	0.18	197	0.34	0.32
	P-value		NS			NS
Fluid type	Straight	1599	0.46	0.17	39	0.34	0.2
	Soluble	1810	0.43	0.20	53 (42b)	0.56 (0.31b)	0.61 (0.08b)
	Synthetic	758	0.40	0.05	119	0.21	0.07
	Semisynthetic	55	0.31	0.09	16	0.31	0.07
	P-value		NS			0.0234 (0.0329)
All	All	6631	0.43	0.17	270 (216b)	0.31 (0.11b)	0.27 (0.11b)

P-value, ANOVA (dependent variable = log-transformed value. NA: not applicable because category of studies = 1, NS: not statistically significant.

^aIncludes milling, drilling, hobbing, tapping, broaching, turning, stamping.

^bResult obtained after unexpected high level (1.53 mg m⁻³) is excluded.