Cena and Peters [2011] evaluated the effectiveness of ventilated enclosures including a Class II, Type A2 BSC and a custom fume hood during the manual sanding of epoxy test samples reinforced with CNTs. Sanding of CNT-epoxy materials released respirable-sized (micronsized) particles but generally no nano-sized particles. The respirable mass concentration in the operator’s breathing zone while using the BSC was approximately two orders of magnitude lower than the concentration when using the custom fume hood. The use of the custom fume hood resulted in an increase of breathing zone concentrations of about one order of magnitude compared to the use of no controls. The custom fume hood had a low average face velocity of about 45 ft/min with high variability across the hood face. The authors suggested that the poor performance of the custom fume hood may have been due to its rudimentary design, which did not include a front sash or rear baffles. The lack of these common fume hood features along with the low average face velocity may have resulted in poor airflow distribution across the face and increased leakage.
Macher and First [1984] evaluated the effect of airflow rates and operator activity on containment effectiveness for a Class II, Type B1 biological safety cabinet using bacterial spores released by two 6-jet collison nebulizers. The hood sash height correlated negatively with the containment effectiveness; that is, the higher of two sash heights provided better containment of the aerosol. In addition, working in the front half of the cabinet provided better protection than working in the rear half of the cabinet. The authors postulated that working in the rear of the hood caused the operator to move closer to the hood opening, blocking the opening and causing more turbulence and leakage around the sides of the hood. The operator withdrawing his arms from the hood caused significantly more leakage than moving arms side to side within the hood. The authors concluded that testing BSCs with persons working at them provides more information than static testing alone and that even well-designed cabinets lose a small fraction of aerosols.
3.4.2.3 Glove Box Isolators
A glove box isolator fully isolates (contains) a small-scale process and is sometimes referred to as a primary protection device (Figure 12) [HSE 2003a]. The design can be either the more typical hard unit or a soft, flexible containment unit (often referred to as a glove bag). Glove boxes provide a high degree of operator protection but at a cost of limited mobility and size of operation. In addition, cleaning the glove box may be difficult, and, to prevent exposures, operators should use caution when transferring materials and equipment into and out of the glove box. In general, glove boxes include a pass-through port, which allows the user to move equipment or supplies into and out of the enclosure.
The performance of a glove box containment system was evaluated during weighing activities of fine lactose powder (a common pharmaceutical surrogate test material). Air samples were collected at four locations: inside the glove box, in the pass-through, in front of the glove box, and at the exit of the recirculating HEPA filter [Walker 2002]. The results of sampling a 10-minute task showed the average concentration measured inside the glove box was 298 µg/ m3, the average concentration in the integral pass-through was 35 µg/m3, and concentrations measured in the room, including downstream of the glove box exhaust, were below the analytical limit of detection of 1 µg/m3. Sample swabs of interior surfaces showed dust 34
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes
