Nano-metal oxides: Exposure and engineering control assessment.

In January 2007, the National Institute for Occupational Safety and Health (NIOSH) conducted a field study to evaluate process specific emissions during the production of ENMs. This study was performed using the nanoparticle emission assessment technique (NEAT). During this study, it was determined that ENMs were released during production and cleaning of the process reactor. Airborne concentrations of silver, nickel, and iron were found both in the employee's personal breathing zone and area samples during reactor cleaning. At the completion of this initial survey, it was suggested that a flanged attachment be added to the local exhaust ventilation system. NIOSH re-evaluated the facility in December 2011 to assess worker exposures following an increase in production rates. This study included a fully comprehensive emissions, exposure, and engineering control evaluation of the entire process. This study made use of the nanoparticle exposure assessment technique (NEAT 2.0). Data obtained from filter-based samples and direct reading instruments indicate that reactor cleanout increased the overall particle concentration in the immediate area. However, it does not appear that these concentrations affect areas outside of the production floor. As the distance between the reactor and the sample location increased, the observed particle number concentration decreased, creating a concentration gradient with respect to the reactor. The results of this study confirm that the flanged attachment on the local exhaust ventilation system served to decrease exposure potential. Given the available toxicological data of the metals evaluated, caution is warranted. One should always keep in mind that occupational exposure levels were not developed specifically for nanoscale particles. With data suggesting that certain nanoparticles may be more toxic than the larger counterparts of the same material; employers should attempt to control emissions of these particles at the source, to limit the potential for exposure.

Airborne exposure patterns from a passenger source in aircraft cabins.

Airflow is a critical factor that influences air quality, airborne contaminant distribution, and disease transmission in commercial airliner cabins. The general aircraft-cabin air-contaminant transport effect model seeks to build exposure-spatial relationships between contaminant sources and receptors, quantify the uncertainty, and provide a platform for incorporation of data from a variety of studies. Knowledge of infection risk to flight crews and passengers is needed to form a coherent response to an unfolding epidemic, and infection risk may have an airborne pathogen exposure component. The general aircraf-tcabin air-contaminant transport effect model was applied to datasets from the University of Illinois and Kansas State University and also to case study information from a flight with probable severe acute respiratory syndrome transmission. Data were fit to regression curves, where the dependent variable was contaminant concentration (normalized for source strength and ventilation rate), and the independent variable was distance between source and measurement locations. The data-driven model showed exposure to viable small droplets and post-evaporation nuclei at a source distance of several rows in a mock-up of a twin-aisle airliner with seven seats per row. Similar behavior was observed in tracer gas, particle experiments, and flight infection data for severe acute respiratory syndrome. The study supports the airborne pathway as part of the matrix of possible disease transmission modes in aircraft cabins.

Particle Emissions from Laboratory Activities Involving Carbon Nanotubes.

This site study was conducted in a chemical laboratory to evaluate nanomaterial emissions from 20-30 nm diameter bundles of single-walled carbon nanotubes (CNTs) during product development activities. Direct-reading instruments were used to monitor the tasks in real time and airborne particles were collected using various methods to characterize released nanomaterials using electron microscopy and elemental carbon (EC) analyses. CNT clusters and a few high aspect ratio particles were identified as being released from some activities. The EC concentration at the source of probe sonication was found to be higher than other activities including weighing, mixing, centrifugation, coating and cutting. Various sampling methods all indicated different levels of CNTs from the activities, however, the sonication process was found to release the highest amounts of CNTs. It can be cautiously concluded that the task of probe sonication possibly released nanomaterials into the laboratory and posed a risk of surface contamination. Based on these results, the sonication of CNT suspension should be covered or conducted inside a ventilated enclosure with proper filtration or a glovebox to minimize the potential of exposure.

The characterization of airborne occupational safety and health hazards in selected small businesses; manufacturing wood pallets.

Researchers from the National Institute for Occupational Safety and Health (NIOSH) investigated occupational safety and health concerns in the small business wood pallet manufacturing industry because of an injury rate (2000) 226% greater than that for general industry. NIOSH investigators conducted walk-through evaluations at seven wood pallet manufacturing companies, and returned to four of them to take environmental measurements. Carbon monoxide (CO) levels, noise levels, and total particulate were measured, ergonomic observations made, and occupational safety practices analyzed at each of the four facilities where measurements were taken. The focus of this study is the evaluation of airborne particulate and carbon monoxide exposures for the purpose of determining areas of potentially high exposures. This knowledge can guide the plant owner or health professional to determine whether further measurements are necessary and where they might be needed. Safety factors and physical stressors (noise and ergonomic stressors) were described in a previously published companion paper. Although we did not take 8 h samples, we did find certain exposures that were potentially of concern to the small business owner. The main findings of this investigation were as follows: 1) CO levels in three plants, for the time periods measured, were less than the OSHA permissible exposure limit (PEL) of 50 parts per million (ppm) for an 8-h TWA. Three measurements, all from one plant, were due to a older and defective forklift and were above 50 ppm. 2) Total dust measures ranged from 0.86 to 1.67 mg/m3, taken adjacent to an operating machine cutting hardwood and measured up to 6 min. The American Conference of Governmental Industrial Hygienists (ACGIH) guideline for hardwood dust is 1.0 mg/m3, again for an 8-h TWA.

Performance of Particulate Containment at Nanotechnology Workplaces.

The evaluation of engineering controls for the production or use of carbon nanotubes (CNTs) was investigated at two facilities. These controls assessments are necessary to evaluate the current status of control performance and to develop proper control strategies for these workplaces. The control systems evaluated in these studies included ventilated enclosures, exterior hoods, and exhaust filtration systems. Activity-based monitoring with direct-reading instruments and filter sampling for microscopy analysis were used to evaluate the effectiveness of control measures at study sites. Our study results showed that weighing CNTs inside the biological safety cabinet can have a 37% reduction on the particle concentration in the worker's breathing zone, and produce a 42% lower area concentration outside the enclosure. The ventilated enclosures used to reduce fugitive emissions from the production furnaces exhibited good containment characteristics when closed, but they failed to contain emissions effectively when opened during product removal/harvesting. The exhaust filtration systems employed for exhausting these ventilated enclosures did not provide promised collection efficiencies for removing engineered nanomaterials from furnace exhaust. The exterior hoods were found to be a challenge for controlling emissions from machining nanocomposites: the downdraft hood effectively contained and removed particles released from the manual cutting process, but using the canopy hood for powered cutting of nanocomposites created 15%-20% higher ultrafine (<500 nm) particle concentrations at the source and at the worker's breathing zone. The microscopy analysis showed that CNTs can only be found at production sources but not at the worker breathing zones during the tasks monitored.

Development of evaluation procedures for local exhaust ventilation for United States postal service mail-processing equipment.

Researchers from the National Institute for Occupational Safety and Health (NIOSH) have conducted several evaluations of local exhaust ventilation (LEV) systems for the United States Postal Service (USPS) since autumn 2001 when (a) terrorist(s) employed the mail system for acts of bioterrorism. As a part of the USPS 2002 Emergency Preparedness Plan, the development and installation of LEV onto USPS mail-processing equipment can reduce future exposures to operators from potentially hazardous contaminants, such as anthrax, which might be emitted during the processing of mail. This article describes how NIOSH field testing led to the development of recommended testing procedures for evaluations of LEV capture efficiency for mail-processing equipment, including tracer gas measurements, smoke release observations, air velocity measurements, and decay-rate testing under access hoods.