Evaluation of Leakage From Fume Hoods Using Tracer Gas, Tracer Nanoparticles and Nanopowder Handling Test Methodologies

Abstract

The most commonly reported control used to minimize workplace exposures to nanomaterials is the chemical fume hood. Studies have shown, however, that significant releases of nanoparticles can occur when materials are handled inside fume hoods. This study evaluated the performance of a new commercially available nano fume hood using three different test protocols. Tracer gas, tracer nanoparticle, and nanopowder handling protocols were used to evaluate the hood. A static test procedure using tracer gas (sulfur hexafluoride) and nanoparticles as well as an active test using an operator handling nanoalumina were conducted. A commercially available particle generator was used to produce sodium chloride tracer nanoparticles. Containment effectiveness was evaluated by sampling both in the breathing zone (BZ) of a mannequin and operator as well as across the hood opening. These containment tests were conducted across a range of hood face velocities (60, 80, and 100 feet/minute) and with the room ventilation system turned off and on. For the tracer gas and tracer nanoparticle tests, leakage was much more prominent on the left side of the hood (closest to the room supply air diffuser) although some leakage was noted on the right side and in the BZ sample locations. During the tracer gas and tracer nanoparticle tests, leakage was primarily noted when the room air conditioner was on for both the low and medium hood exhaust air flows. When the room air conditioner was turned off, the static tracer gas tests showed good containment across most test conditions. The tracer gas and nanoparticle test results were well correlated showing hood leakage under the same conditions and at the same sample locations. The impact of a room air conditioner was demonstrated with containment being adversely impacted during the use of room air ventilation. The tracer nanoparticle approach is a simple method requiring minimal setup and instrumentation. However, the method requires the reduction in background concentrations to allow for increased sensitivity.

In-depth survey report: containment assessment of nanomaterial handling enclosures at academic research laboratories using carbon nanotubes and graphene.

“…These enclosures typically operate between 0.36-0.41 m/s on average at the enclosure face opening. A recently published study evaluating a nanomaterial handling enclosure, similar to those seen in these labs, showed that an average face velocity of 0.30 m/s was not adequate to prevent the escape of tracer nanoparticles or tracer gas when a room air supply diffuser was located above the hood face (Dunn, Tsai et al 2014). Even at an average face velocity of 0.41 m/s, some face leakage was identified.…”

The Effectiveness of Specific Risk Mitigation Techniques Used in the Production and Handling of Manufactured Nanomaterials: A Systematic Review

“…One paper on an international survey regarding occupational health and safety programs, engineering controls and PPE, did not contain data on the concentrations of airborne MNMs particles [13] and could not be used for the calculation of PFs. The remaining 14 papers reported on: enclosure systems (down flow clean rooms with ventilated enclosure hood); ventilation (LEV, enclosure type LEV with proper face velocity, process ventilation, biosafety cabinets); specialized ventilation systems (thermal displacement ventilation); and segregation sources (reactor cabinets) [7][8][9][10][11][12][14][15][16][17][18][19][20][21].…”

“…2 means there was no leak, as described in the papers. The recommended face velocity of the enclosure type LEVs ranged from 0.4 to 0.6 m/s [7,[16][17][18]. One paper concluded that a canopy hood for nanocomposite cutting led to an increase in exposure (PF = 0.8) [17].…”

Effects of a Manikin on the Capture Efficiency and Protection Efficiency of a Small Rectangular Hood

“…Studies considering aerosol tracers as a method for determining hood effectiveness are very limited (Bemer et. al., 1998;Dunn et. al, 2014).…”

“…al. (1998) did not consider the effects of cross drafts, the effects of varying hood fan rates, the effects of orientation, or the effects of operator presence; only ideal conditions were considered Dunn et. al.…”