National Institute of Occupational Safety and Health

“ In addition to direct-reading instrument measurements, nanoparticle emissions can also be characterized using off-line analysis techniques. Off-line analysis methods can determine the physical and chemical properties of airborne nanomaterials, such as particle size, shape, surface area, composition, and agglomeration state. These properties are useful to evaluate exposure and toxicology of nanomaterials in the workplace. Off-line analysis can also be useful in separating background nanomaterials from engineered nanomaterials, based on size, shape, morphology, etc. ”

“ Airflow visualization techniques can be used to help understand the patterns of airflow in and around exhaust hoods and pressure differences between adjacent areas/rooms. Smoke can be released around the edge of, or inside of, a local exhaust hood to visualize the airflow patterns. ”

“ Currently, it is unclear which metrics associated with exposures to engineered nanomaterials are most important from a health and safety perspective. The mass-based metric is traditionally used to characterize toxicological effects of exposure to air contaminants. Animal in vivo exposure studies and cell-culture-based in vitro experiments show that size and shape are the two major factors influencing toxicological effects of engineered nanomaterials. ”

“ Sampling quality is always an issue for field evaluation. High-quality sampling results can be obtained by following certain steps. The sampling data can only be trusted by using instruments that have been calibrated for nanoparticle sampling before use. Factory calibration for particle counters and sizers typically uses reference materials having a range of particle sizes. If possible, the instruments should be calibrated with the target nanomaterials in the laboratory before using them for field study. ”

“ Special attention should be paid in subsequent tracer gas testing and air velocity measurements to locations where smoke release observations indicate poor or marginal capture efficiency. In addition, video may be taken of airflow visualization tests to provide feedback information to the company on system performance and factors that negatively affect hood performance.
Another use for airflow visualization is the evaluation of room pressurization status. It is recommended that rooms where nanomaterials are used be kept at an atmospheric pressure that is lower than adjacent areas. ”

“ The effectiveness of engineering controls for reducing exposures to nanomaterials during manufacturing and handling has not been widely investigated. To evaluate control measures in nanomanufacturing facilities, investigators need to collect both quantitative and qualitative data to describe nanoparticle emissions. Accurate direct-reading instruments allow investigators to identify the source of contamination in real time for various task scenarios. ”

“ Accurate duct velocity can be obtained using this method; however, poor measuring locations will cause inaccurate estimates of exhaust air flow. Sometimes the airflow through a hood can only be determined by measuring the air velocity at the hood face.
The measurement of fume hood face velocity is an important method to assess proper operation and containment. The average hood face velocity can be measured by dividing the opening of the hood into equal area grids of approximately one square foot and logging the velocity at the center of each grid with the thermal anemometer. ”

“ Ideally, filter samples can be taken at the same location as area monitoring with direct-reading instruments to make a side-by-side comparison.
4.1.3 Air Monitoring and Filter Sampling
The selection of direct-reading instruments (Table 3) for field evaluation must cover a wide range of particle sizes. Particle diffusion occurs rapidly when nanoparticles are released in the workplace. It results in nanomaterial agglomerates because of particle collisions. For example, the average particle size (or size distribution) is larger during product transfer than right after product harvesting. ”

“ Another example is the scanning monitoring particle sizer (SMPS) , which uses a radioactive source to bring the sampling aerosol to charge equilibrium. This can make shipping difficult. Sometimes it can be difficult to obtain quantifiable mass concentrations of nanomaterials in the workplace using impactor sampling. Newly developed devices, such as photometers, can detect nanoparticles as small as 50−100 nm with resolution around 1 μg/m3. These instruments can provide continuous monitoring for real-time mass concentrations. ”

“ In addition to the quantitative capture method, qualitative methods, such as smoke release or dry ice tests, are often used to evaluate air movement. Smoke generation and capture is a method often used to qualitatively evaluate the performance of ventilation controls [Marzal et al. 2003a; Woods and Mckarns 1995] . ”