In this study, the ratios of inhalable, thoracic, and respirable fractions were used to estimate workers’ thoracic (Cthor) and respirable (Cresp) fractions ofoilmistconcentrations based on concentrations of the inhalable fraction (Cinh) that were directly obtained from personal samplings。 Finally based on the definitions given above for inhalable, thoracic and res- pirable aerosols, the concentrations ofoilmistsexposed to the head region (Chead = Cinh − Cthor), tracheobronchial region

(Ctb = Cthor − Cresp), and alveolar region (Calv = Cres) foreach

selected worker were estimated。

3。Results and discussion

3。1。Oil mist concentration profiles for fastener manufacturing industry workers

Table 2 shows the concentration profiles of the three selected exposure groups。 The magnitude of AMMVUE shown in sequence was found as: threading workers (=2。11 mg/m3)> forming workers (=1。58 mg/m3) > heat treatment workers (=0。0801 mg/m3)。 Obviously, the above concentrations were consistently lower than the permissible exposure level adopted by OSHA, NIOSH, ACGIH, HSE,andTaiwan government (=5 mg/m3) and that adopted by JOSH (=3 mg/m3)。 Neverthe- less, the levels for both threading and forming workers were much higher than that for steel millers (=0。27–1。6 mg/m3), ferry-engine-maintenance workers (=0。45 mg/m3), overall ship- engine-maintenance workers (=0。24 mg/m3), and tunnel con- struction workers (=0。070–1。4 mg/m3), with the exception for both cable manufacturing workers (=2。25 mg/m3) and car- making workers (=2。6 mg/m3) (Table 1)。 Here, it should be noted that Oudyk et al。 [30] has found the occurrence of upper respiratory tract symptoms (such as asthma and sore throat, etc。) in workers exposed to total oil mist concentrations of

Table 2

Mean personal inhaled oil mist concentrations (AMMVUE) and their 95% confidence intervals (95% CI) for workers of the three selected exposure groups in the fastener manufacturing industry (mg/m3)

Statistics Forming (n = 17) Threading (n = 11) Heat treatment (n = 6)

AMMVUE 1。58 2。11 0。0801

95% C。I。 1。47–1。71 1。89–2。40 0。0546–0。174

Log-normality Yes Yes Yes

Fig。 1。 Particle size distribution of oil mists obtained from the forming, thread- ing, and heat treatment processes in the fastener manufacturing industry。

0。25–0。84 mg/m3。 Skyberg et al。 [31] suggest that the possibility of inducing lung fibrosis in workers while exposed to total oil mist concentrations of 0。15–0。30 mg/m3。 Particularly in 2001, ACGIH proposed to lower down the oil mist threshold limit value to 0。2 mg/m3 [32]。 The above information warrants the need to further assess health hazards imposed on fastener manufacturing industry workers in the future。

In this study, we found that the concentrations of the inhaled oil mists for threading workers were significantly higher than that for forming workers (nonparametric Mann–Whitney test, p < 0。05)。 However, we found that the operation of the tread- ing machine involved less mechanical impaction forces than the forming machine。 In addition, the measured surface tempera-

tures on the molder of the forming machine (=75。8 ± 19。8 ◦C)

werehigherthanthetemperaturesonthesurfaceof the

threading gear (=69。6 ± 17。1 ◦C), and both workplaces shared very similar environmental temperatures (=32。2 ± 1。48 ◦C and