Abstract
For the appropriate hygienic management of workplaces where workers handled nano-TiO2 products, the status of the personal exposure of workers to respirable dust (PM4) and nanoparticles (PM0.1) was investigated. Using a cyclone sampler for PM4 and a personal sampler for PM0.1, PM4 and PM0.1 exposure levels were evaluated to discuss them in relation to worker’s duties. The number of particles of 0.01–10 µm was also monitored online in order to examine the short-term fluctuation in the concentration and size distribution of particles. The 8h-time-weighted average (TWA) and 95% upper limit for respirable dust exposure were below the occupational exposure limit specified by the Japan Society for Occupational Health and the recommended exposure limits for TWA by NIOSH. The action level was exceeded during the filling of a flexible container bag. More than 70% of particles in the breathing zone was coarse agglomerates of > 1 µm, while it may be influenced by powder properties and the handling process as well as the management of local ventilation. The maximum PM0.1 concentration (31.3 µg m–3) occurred in a powder filling booth without air ventilation. The operation of a gasoline powered forklift temporarily increased the concentration of ultrafine particles. Most of TiO2 powder was suspended as micron-order agglomerates in the breathing zone. However, since PM0.1 exposure was much larger than those in outdoor environment particularly under insufficient cares to aerosolized powder and air ventilation, PM0.1 exposure should also be monitored.
Highlights
According to the development of nanomaterial manufacturing technologies (Ding et al, 2017), existing procedures for occupational exposure to airborne particulates have been requested to be updated by the nanomaterials industries (Leidel et al, 1977; British Occupational Hygiene Society, 1996; BSI, 1996; MHLW, 2010; AIHA, 2015; Japan Society for Occupational Health (JSOH), 2015)
The 8 hour time-weighted average (8hTWA) for Worker-B1 and -B2 in 2012 were, respectively, 247 and μg m–3, each of which cleared the occupational exposure limit (OEL) and recommended exposure limit of time-weighted average (REL-TWA) but exceeded the action level (AL, μg m–3) defined as 50% of the OEL for Worker-B1, where the AL is generally defined as 50% of the permissible-exposure level (PEL) (NIOSH, 1975)
Since 2014, the packing booth has been protected by transparent vinyl curtains so that it had a local ventilation system that was operated at the suction velocity that was measured at the inlet of the ventilator hood
Summary
According to the development of nanomaterial manufacturing technologies (Ding et al, 2017), existing procedures for occupational exposure to airborne particulates have been requested to be updated by the nanomaterials industries (Leidel et al, 1977; British Occupational Hygiene Society, 1996; BSI, 1996; MHLW, 2010; AIHA, 2015; JSOH, 2015). Very few case studies of breathing zone sampling of workers based on the actual measurement of worker’s exposure to NPs have been reported for nano-TiO2 Ichihara et al (2016) evaluated the personal exposure to nano-TiO2 using a Siutas cascade impactor for particles < 250 nm The reason for this is that only a few portable tools are available for measuring the degree of exposure to nanoparticles (< 100 nm) in the breathing zone of a worker and only a few commercial products capable of measuring nanoparticles are currently available (Furuuchi et al, 2010a; Tsai et al, 2011, 2012; Young et al, 2013; Thongyen et al, 2015; Asbach et al, 2017). The number concentration of particles in the 10 nm–10 μm size range was monitored online using a scanning mobility particle sizer and an optical particle counter at selected locations including various locations in the workplace in order to evaluate fluctuations in the concentration and size distribution of particles in relation to workers’ activities
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