Exposure controls for nanomaterials at three manufacturing sites

Abstract

Because nanomaterials are thought to be more biologically active than their larger parent compounds, careful control of exposures to nanomaterials is recommended. Field studies were conducted at three sites to develop information about the effectiveness of control measures including process changes, a downflow room, a ventilated enclosure, and an enclosed reactor. Aerosol mass and number concentrations were measured during specific operations with a photometer and an electrical mobility particle sizer to provide concentration measurements across a broad range of sizes (from 5.6 nm to 30 μm). At site A, the dust exposure and during product harvesting was eliminated by implementing a wait time of 30 -min following process completion. And, the dust exposure attributed to process tank cleaning was reduced from 0.7 to 0.2 mg/m3 by operating the available process ventilation during this task. At site B, a ventilated enclosure was used to control dust generated by the manual weigh-out and manipulation of powdered nanomaterials inside of a downflow room. Dust exposures were at room background (under 0.04 mg/m3 and 500 particles/cm3) during these tasks however, manipulations conducted outside of the enclosure were correlated with a transient increase in concentration measured at the source. At site C, a digitally controlled reactor was used to produce aligned carbon nanotubes. This reactor was a closed system and the ventilation functioned as a redundant control measure. Process emissions were well controlled by this system with the exception of increased concentrations measured during the unloading of the product. However, this emission source could be easily controlled through increasing cabinet ventilation. The identification and adoption of effective control technologies is an important first step in reducing the risk associated with worker exposure to engineered nanoparticles. Properly designing and evaluating the effectiveness of these controls is a key component in a comprehensive health and safety program.

Keywords: airborne contaminants; control evaluation; engineered nanomaterials; engineering controls; hazard prevention.

FIGURE 1

Schematic illustration of process flow at Site A: (a) Process A; and (b) Processes B with design features that may minimize dust exposures. Note: The butterfly valves can be closed during product recovery so that process containment is maintained.

FIGURE 2

Layout of the downflow room at Site B.

FIGURE 3

Schematic illustration of Easy Tube 3000 Reactor (CVD Equipment Corporation, Ronkonkoma, NY) used at Site C. Note: the reactor cabinet’s exhaust air enters through slots behind the filtration module that sits on top of the Load compartment cabinet.

FIGURE 4

Dust exposure measured at source with (a) DustTrak and (b) FMPS during product harvesting from processes and product transfer inside a ventilated enclosure at Site A.

FIGURE 5

Real-time monitoring of nanomaterials released from the cleaning for Process tank A at Site A. The cleaning process was performed (a) without and (b) with the use of the process ventilation.

FIGURE 6

Aerosol concentrations measured during powder weigh-out at Site B.

FIGURE 7

Particle (A) number and (B) mass concentrations in front of reactor at Site C: Task A – routine operation of reactor, Task B – loading and unloading of reactor, and Task C – away from reactor during other activities.

FIGURE 8

Flexible enclosure for product harvesting.