ABSTRACT
Introduction
Laboratory fume hoods are mechanical devices used to extract harmful vapours from
indoor workplaces in order to prevent human exposure thereto. Laboratory fume hoods
are considered an engineering control in the hierarchy of control and are ubiquitous in the
modern laboratory. Protection offered by the fume hood depends on whether it is
performing according to its original design. This performance needs to be maintained for
as long as the fume hood is in use. Gaining a better understanding of this performance
and the limitations of the fume hood are essential in ensuring constant operator
protection.
No performance or measurement standard to which fume hoods need to comply exists in
South Africa. The Occupational Health and Safety Act, 1993 (Act no. 85 of 1993)
requires engineering controls to be evaluated every 24 months. The Act does not stipulate
how such evaluations need to be conducted.
The Forensic Science Laboratory (FSL) of the South African Police Service has 49 fume
hoods installed in its facility in Silverton, Pretoria. The FSL set a performance standard
for its fume hoods at 0.51 m.s-1 ± 20% average across the face of the fume hood. The FSL
selected the ANSI/ASHRAE 110 test method to evaluate the performance of its fume
hoods against this standard.
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Objectives
The first objective of the study was to measure face velocities of fume hoods as installed
in a forensic science laboratory and calculate the averages, and to determine whether
these comply with the set standard.
The second objective was to measure face velocities of fume hoods as installed in a
forensic science laboratory and calculate the average in order to determine their
performance over time.
The third study objective was to observe laboratory fume hoods as installed in a forensic
science laboratory to see whether fans were operational each month for 11 months (i.e.
down time).
Methods
10 Observations and 10 tests were carried out on each fume hood. Observations related to
whether fume hood fans were functioning or not. Testing was a measure of performance
and required the actual measurement of face velocities. A calibrated thermal anemometer
was used to take velocity measurements. Measurements taken represent standard
velocities. Fume hood faces were divided into imaginary grids not exceeding 30 cm x 30
cm. Velocity measurements were taken at the centre points of these grids. The arithmetic
means were calculated for these measurements. The mean of the test means was then
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calculated for every fume hood. This, so that a comparison could be made between the
mean and the set standard.
Observations indicated that at the onset of the study 14% of fume hoods were not
operational. By the end of the study 27% were not operational. A decline of 13% over the
study period. At one point during the study 47% of the fume hoods were not functioning.
Results
82% of the fume hood population performed outside the standard. 12% underperformed
at less than 0.41 m.s-1 while 70% overperformed at velocities exceeding 0.61 m.s-1.
ANOVA and regression analyses revealed that performance of the fume hoods over time
remained fairly constant (e.g. regression analyses p-value = 0.8538).
Discussion and conclusion
Fume hood operability and performance results indicate the need for urgent investigation
into the correct use of this resource within the FSL. Results are less than satisfactory with
the health of laboratory personnel being potentially compromised. Comprehensive
procurement, installation, operating and testing procedures need to be compiled, or if
available, reviewed and implemented. Further study into the performance of the fume
hoods may also be necessary using additional performance indicators.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/5966 |
| Date | 23 January 2009 |
| Creators | Jacobs, Peter John |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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