Particles in a box: novel design and evaluation of an adaptable engineering control enclosure for a common split tube furnace to eliminate occupational exposure to refractory ceramic insulation fibers†

Split tube furnaces, which rely on insulation commonly made of refractory ceramic fiber (RCF) material, are routinely used in nanotechnology laboratories to generate carbon-based nanomaterials and other manmade materials through chemical vapor deposition (CVD) processes. RCF aerosols can pose a use-phase inhalation risk to operators. We quantified the inhalation exposure risk and designed, built, and tested the impact of a benchtop ventilated enclosure for a common split tube furnace. Direct real-time measurements revealed that traditional use of the furnace could result in peak RCF total and respirable fraction particle mean concentrations of 25 ± 10 mg m⁻³ and 11 ± 4 mg m⁻³, respectively (n = 50). Employment of the ventilated enclosure reduces instantaneous exposure to total RCF dust and the respirable fraction to approximately baseline values: 0.006 mg m⁻³ ± 0.003 mg m⁻³, and 0.003 mg m⁻³ ± 0.002 mg m⁻³, respectively (n = 30). The peak concentration of suspended particulate matter is highly variable over uniform release triggers, ranging from 5–50 mg m⁻³ for PM_TOTAL and 2–18 mg m⁻³ for PM_RESPIRABLE. Electron microscopic examinations of collected airborne materials were conducted to count the airborne number concentrations of RCFs greater than 5 μm in length, less than 3 μm in width, and that met a 5 : 1 length : width aspect ratio minimum, which are of toxicological concern. Concentrations of those RCFs were similarly reduced when the enclosure was in place. Technical drawings and specifications of the split tube furnace enclosure design are available for ready recreation and implementation, in light industry or laboratory settings, thereby providing low-cost modification to protect the health of workers and researchers.