ABSTRACTudIntroductionudLaboratory fume hoods are mechanical devices used to extract harmful vapours fromudindoor workplaces in order to prevent human exposure thereto. Laboratory fume hoodsudare considered an engineering control in the hierarchy of control and are ubiquitous in theudmodern laboratory. Protection offered by the fume hood depends on whether it isudperforming according to its original design. This performance needs to be maintained forudas long as the fume hood is in use. Gaining a better understanding of this performanceudand the limitations of the fume hood are essential in ensuring constant operatorudprotection.udNo performance or measurement standard to which fume hoods need to comply exists inudSouth Africa. The Occupational Health and Safety Act, 1993 (Act no. 85 of 1993)udrequires engineering controls to be evaluated every 24 months. The Act does not stipulateudhow such evaluations need to be conducted.udThe Forensic Science Laboratory (FSL) of the South African Police Service has 49 fumeudhoods installed in its facility in Silverton, Pretoria. The FSL set a performance standardudfor its fume hoods at 0.51 m.s-1 ± 20% average across the face of the fume hood. The FSLudselected the ANSI/ASHRAE 110 test method to evaluate the performance of its fumeudhoods against this standard.udvudObjectivesudThe first objective of the study was to measure face velocities of fume hoods as installedudin a forensic science laboratory and calculate the averages, and to determine whetherudthese comply with the set standard.udThe second objective was to measure face velocities of fume hoods as installed in audforensic science laboratory and calculate the average in order to determine theirudperformance over time.udThe third study objective was to observe laboratory fume hoods as installed in a forensicudscience laboratory to see whether fans were operational each month for 11 months (i.e.uddown time).udMethodsud10 Observations and 10 tests were carried out on each fume hood. Observations related toudwhether fume hood fans were functioning or not. Testing was a measure of performanceudand required the actual measurement of face velocities. A calibrated thermal anemometerudwas used to take velocity measurements. Measurements taken represent standardudvelocities. Fume hood faces were divided into imaginary grids not exceeding 30 cm x 30udcm. Velocity measurements were taken at the centre points of these grids. The arithmeticudmeans were calculated for these measurements. The mean of the test means was thenudviudcalculated for every fume hood. This, so that a comparison could be made between theudmean and the set standard.udObservations indicated that at the onset of the study 14% of fume hoods were notudoperational. By the end of the study 27% were not operational. A decline of 13% over theudstudy period. At one point during the study 47% of the fume hoods were not functioning.udResultsud82% of the fume hood population performed outside the standard. 12% underperformedudat less than 0.41 m.s-1 while 70% overperformed at velocities exceeding 0.61 m.s-1.udANOVA and regression analyses revealed that performance of the fume hoods over timeudremained fairly constant (e.g. regression analyses p-value = 0.8538).udDiscussion and conclusionudFume hood operability and performance results indicate the need for urgent investigationudinto the correct use of this resource within the FSL. Results are less than satisfactory withudthe health of laboratory personnel being potentially compromised. Comprehensiveudprocurement, installation, operating and testing procedures need to be compiled, or ifudavailable, reviewed and implemented. Further study into the performance of the fumeudhoods may also be necessary using additional performance indicators.
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