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This study was performed in a climatic chamber to evaluate the combined effects of noise intensity, heat stress, workload, and exposure duration on both noise-induced temporary threshold shift (TTS) and the recovery time by adopting Taguch's method. Fourteen subjects without previous significant noise exposure and smoking history were recruited to participate in this study. All hearing threshold levels at eight different frequencies (250 to 8,000 Hz) of better ear were measured in an audiometric booth by using the ascending method in 2 dB steps before each exposure condition. The test was also carried out after exposure to evaluate TTS at various times. The TTS recovery time was assessed using an audiometric test on all subjects at post-exposure times of 2, 20, 40, 60, 80 and 120 min, respectively. It was found that TTS depended mainly on the exposed noise dose and was enhanced by workload and heat stress. The TTS recovery time is dependent upon the magnitude of the initial hearing loss. In conclusion, TTS driven by noise exposure is enhanced by heat and workload. Further studies are required to evaluate the effects of workload with extreme temperature in a workplace environment.

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The purpose of this study is to evaluate the non-ionizing radiation (NIR) exposure, especially optical radiation levels, and potential health hazard from aluminum arc welding processes based on the American Conference of Governmental Industrial Hygienists (ACGIH) method. The irradiance from the optical radiation emissions can be calculated with various biological effective parameters [i.e., S(lambda), B(lambda), R(lambda)] for NIR hazard assessments. The aluminum arc welding processing scatters bright light with NIR emission including ultraviolet radiation (UVR), visible, and infrared spectra. The UVR effective irradiance (Eeff) has a mean value of 1,100 microW cm at 100 cm distance from the arc spot. The maximum allowance time (tmax) is 2.79 s according to the ACGIH guideline. Blue-light hazard effective irradiance (EBlue) has a mean value of 1840 microW cm (300-700 nm) at 100 cm with a tmax of 5.45 s exposure allowance. Retinal thermal hazard effective calculation shows mean values of 320 mW cm(-2) sr(-1) and 25.4 mW (cm-2) (380-875 nm) for LRetina (spectral radiance) and ERetina (spectral irradiance), respectively. From this study, the NIR measurement from welding optical radiation emissions has been established to evaluate separate types of hazards to the eye and skin simultaneously. The NIR exposure assessment can be applied to other optical emissions from industrial sources. The data from welding assessment strongly suggest employees involved in aluminum welding processing must be fitted with appropriate personal protection devices such as masks and gloves to prevent serious injuries of the skin and eyes upon intense optical exposure.

This study reports a method for constructing a head model with a continuous airway passage beginning from the nostrils and continuing through the second generation of bronchi, using computerized tomographic (CT) images of facial features and airway passages from a healthy Taiwanese male adult. When combined with a manikin torso and connected to a cyclic breathing machine, the Taiwanese head model can simulate human breathing movement. This model enables investigation of important parameters of deposition efficiency without the inter- and intrasubject variability that often occurs in human studies. Being an assembly of numerous polymethyl methacrylate (PMMA) plastic slabs, the head model can be applied to study particle deposition at specified respiratory regions. The nasal geometry obtained in this study was compared with those obtained in other studies, which demonstrated this head model to be 36% smaller in nostril cross-sectional area than for European Americans. Additionally, this Taiwanese head model was found to be shorter in nasal cavity length, and the minimum cross-sectional area was only 50% compared to that of European Americans. This study also measured the nasal inhalation efficiency and deposition for particles ranging from 1.5 to 15 microm under various ventilation levels to test the feasibility of this head model. Future particle deposition studies using this Taiwanese head model can be compared with the currently available data, which are primarily based on Caucasian cast models or human subjects.