Feasibility of Substituting Ethylene with SulfurHexa Fluoride as a Tracer Gas in Hood Performance Test by ASHRAE-110-95 Method

ANSI/ASHRAE 110-95 protocol is a widely acceptable method to assess the performance of laboratory hoods. In this test, sulfur hexafluoride (SF6) is applied as a tracer gas to quantitatively evaluate the performance of laboratory hoods. The environmentally hostile characteristics of SF6 as well as its cost are the major concerns. In the present study, the substitution of ethylene with SF6 in the ASHRAE 110-95 test method was investigated. Both SF6 and ethylene were applied to a laboratory hood at different face velocities and injection flow rates according to the ASHRAE 110-95 method. Meanwhile, the exposure of a mannequin stationed at the front of hood was measured. The concentration of tracer gases was measured using direct reading instruments. Linear regression of the results was used to consider the substitution of ethylene withSF6.The occupational exposure of the proposed hood operator to SF6 and ethylene were 4.2-7.3 ppm and 0.1 to 0.57 ppm respectively. SF6 exposure was increased significantly (p<0.001) by increasing the injected level while ethylene exposure was decreased significantly (p<0.001). The linear correlation between the leakage levels of two tracer gases at the injected flow rate of 4 lit/min did not fit well with experimental data. Ethylene is not recommended as a substitution for SF6 in ASHRAE 110-95 hood performance test.