Tracer Gas Tests Research Articles

Investigation of the accuracy of BAS-grade CO2 sensors for measuring infiltration rates

Carbon dioxide (CO2) sensors used in building automation systems (BAS) and occupant-generated CO2 allow for a low-cost and environmentally friendly method for continuously monitoring the air leakage of the building envelope in commercial buildings. However, the validity of this method is hindered by the potential inaccuracies of BAS-grade CO2 sensor measurements. This paper presents a comprehensive laboratory study that compares the accuracy of air changes per hour (ACH) measured using CO2 and BAS-grade CO2 sensors to that of SF6 and expensive lab-grade equipment (photoacoustic gas monitor). The results show that CO2 is a suitable alternative to SF6 when using lab-grade equipment. On average, ACH measured with lab-grade CO2 equipment were ±4.5 % of those measured with lab-grade SF6 measurements and 90 % of measurements were within ±10 %. However, the results also indicated that methods to correct for sensor drift are required to improve ACH measurement accuracy when using BAS-grade CO2 sensors that have not undergone routine calibration. By applying a method to correct for sensor drift, ACH measured with BAS-grade CO2 sensors were improved from ±10.9 % to ±5.1 % (on average) and the percentage of measurements within ±10 % increased from 48 % to 83 %. In addition, an environmental impact assessment of the tracer gas tests conducted in this study provides quantitative evidence to support the need to transition away from SF6-based tracer gas tests. The assessment showed that in this study releasing SF6 was ∼177 times worse for the environment than releasing CO2.

Onsite measurement and dilution-based infection risk assessment for a new mobile negative pressure isolation room (MNPIR) as a solution to minimize cross-infection

This study proposes an onsite measurement protocol and infection risk assessment using tracer gas tests based on the dilution-based method to evaluate the ventilation system's performance in the mobile negative pressure isolation room (MNPIR) and minimize infection risk for health care workers (HCW). The dilution-based infection risk assessment is better in determining spatial distribution of infection risk compared to the Wells-Riley model. The study shows that ventilation effectiveness to reduce the infection risk for HCWs can be reviewed using four onsite measurement protocols and a dilution-based infection risk assessment. Optimizing the SA and EA installation locations is key to reducing the cross-infection risk of HCWs, and the contaminant removal effectiveness (CRE) index averaged 2.6, indicating adequate ventilation efficiency. By applying an appropriate ventilation system, the infection risk in HCW spaces was reduced to 50% or less of the average risk (by the Wells-Riley model). The proposed approach allows for quantitative evaluation of infection risk by location and exposure time, demonstrating that the MNPIR can effectively minimize infection risk for HCWs. The study suggests follow-up research on cooling and heating strategies that consider both patient comfort and effective ventilation performance in the MNPIR.

Evaluating methods for estimating whole house air infiltration rates in summer: implications for overheating and indoor air quality

PurposeAccurate values for infiltration rate are important to reliably estimate heat losses from buildings. Infiltration rate is rarely measured directly, and instead is usually estimated using algorithms or data from fan pressurisation tests. However, there is growing evidence that the commonly used methods for estimating infiltration rate are inaccurate in UK dwellings. Furthermore, most prior research was conducted during the winter season or relies on single measurements in each dwelling. Infiltration rates also affect the likelihood and severity of summertime overheating. The purpose of this work is to measure infiltration rates in summer, to compare this to different infiltration estimation methods, and to quantify the differences.Design/methodology/approachFifteen whole house tracer gas tests were undertaken in the same test house during spring and summer to measure the whole building infiltration rate. Eleven infiltration estimation methods were used to predict infiltration rate, and these were compared to the measured values. Most, but not all, infiltration estimation methods relied on data from fan pressurisation (blower door) tests. A further four tracer gas tests were also done with trickle vents open to allow for comment on indoor air quality, but not compared to infiltration estimation methods.FindingsThe eleven estimation methods predicted infiltration rates between 64 and 208% higher than measured. The ASHRAE Enhanced derived infiltration rate (0.41 ach) was closest to the measured value of 0.25 ach, but still significantly different. The infiltration rate predicted by the “divide-by-20” rule of thumb, which is commonly used in the UK, was second furthest from the measured value at 0.73 ach. Indoor air quality is likely to be unsatisfactory in summer when windows are closed, even if trickle vents are open.Practical implicationsThe findings have implications for those using dynamic thermal modelling to predict summertime overheating who, in the absence of a directly measured value for infiltration rate (i.e. by tracer gas), currently commonly use infiltration estimation methods such as the “divide-by-20” rule. Therefore, infiltration may be overestimated resulting in overheating risk and indoor air quality being incorrectly predicted.Originality/valueDirect measurement of air infiltration rate is rare, especially multiple tests in a single home. Past measurements have invariably focused on the winter heating season. This work is original in that the tracer gas technique used to measure infiltration rate many times in a single dwelling during the summer. This work is also original in that it quantifies both the infiltration rate and its variability, and compares these to values produced by eleven infiltration estimation methods.

An inquiry into the use of indoor CO2 and humidity ratio trend data with inverse modelling to estimate air infiltration

Air infiltration has a significant impact on building energy performance and the indoor environment. An accurate estimate of air infiltration rate informs envelope retrofit decisions to improve airtightness. However, air mobility and other environmental factors, such as wind or indoor-outdoor temperature differences, often make the accurate measurement of air infiltration challenging. Further, conventional air infiltration testing approaches such as fan pressurization and tracer gas tests possess certain drawbacks limiting their applicability in commercial buildings. To address the limitations of air infiltration tests, this study proposes a low-cost inverse model-based approach for estimating air infiltration rates by extracting the naturally occurring indoor CO2 and relative humidity (RH) data from a building automation system (BAS). These data were used to develop a linear regression model, and a tracer gas experiment was also used to verify the applicability of the proposed approach. The results indicated that the proposed method could conveniently lend itself to estimate air infiltration rates at a reasonable accuracy using existing CO2 data; however, humidity ratio data (converted from RH and temperature sensor measurements) may only help to track building infiltration characteristics over time due to inaccuracies caused by adsorptive and desorptive properties of various building materials.

Estimation of the infiltration rate of UK homes with the divide-by-20 rule and its comparison with site measurements

Buildings are responsible for 40% of the global energy usage to which infiltration-caused heat losses are responsible for 30%. Air infiltration is the unintended flow of air through leakage paths and fundamentally determined by the airtightness of a building. In the United Kingdom, building airtightness is conventionally measured through a blower door test and used to predict air infiltration in conjunction with the divided-by-20 rule, which is a rule of thumb that has been adopted by SAP (Standard Assessment Procedure: a UK government's recommended method system for measuring the energy rating of residential dwellings) for the estimation of the infiltration-caused heat losses for dwellings. This paper assesses the representativeness of this rule of thumb by carrying out blower door and tracer gas tests in twenty one dwellings located in the East Midlands Region of the United Kingdom. Results showed that a divide-by-37 rule would be more representative. It was also seen that the air infiltration rate is overestimated by SAP when modifying factors are added. The errors are as high as 500% in some cases. The most affected dwellings were the tighter ones. A revision of the usage of the divide-by-20 rule and the modifying factors is advised.

Research on air infiltration predictive models for residential building at different pressure

The pressure difference in buildings under natural state is usually below 10 Pa, and the air change rate at 50 Pa (ACH50) is often used to evaluate building airtightness. There is a dearth of research on air infiltration predictive model at different pressures in China. Moreover, the airflow coefficient (C), a key parameter for air infiltration, is necessary to determine ACH50. Based on prior experimental data, several methods including ordinary least squares (OLS), stepwise regression, partial least squares (PLS) and nonlinear fitting with independent variable screening methods, were employed to establish an airflow coefficient model. The determination coefficient (R2) and the variation coefficient of the root-mean-square error (CV(RMSE)) of these models were compared. The simulation results show that R2 of the airflow coefficient models for apartments and villas increased by a maximum of 25.9% and 2.3%, respectively, using PLS method. The improvement with nonlinear fitting was weaker. Based on K-P model, a conversion model between ACH50 and ACH4 was developed as an air infiltration predictive model under natural state. Blower door and tracer gas tests were conducted to verify the conversion model. The expected error was approximately 10%, which may be caused by measurement errors and shielding from surrounding obstructions. Further studies need to focus on obtaining more experimental data for building airtightness and developing a conversion model for high-rise residential buildings.

Developing a new passive tracer gas test for air change rate measurement

Ventilation is critical in interpreting indoor air quality (IAQ), yet most IAQ assessments do not report ventilation adequately. Most ventilation assessments use tracer gas tests (TGT) to measure total air change rate (ACH), but currently applied TGTs present three shortcomings: limited comparability between ACH and IAQ data, inadequate substances employed as tracer gases and tendency to bias arising from perfect-mixing assumption. This paper proposes a new TGT approach, employing an alternative tracer gas that is captured/analysed using commercial passive IAQ-samplers and including a careful planning-phase to account for imperfect-mixing. Two substances were selected as potential alternative tracers: 2-butoxyethyl-acetate (EGBEA) and deuterated decane (D-decane). Tracer-source tests were performed in lab, enabling enhancements to the source design. Results indicated RH influence over the emissions rates, and EGBEA’s use as tracer was discarded due to hygroscopy. Further work includes evaluating D-decane’s behaviour under varying conditions and computer-simulating TGTs to study the imperfect-mixing effects.

Biofiltration of diluted landfill gas in an active loaded open-bed compost filter

Microbial oxidation in a biofilter is a treatment solution for diluted landfill gas (LFG), for instance at old landfills, where LFG recovery is no longer feasible, or from remediation systems designed to cut off laterally migrating LFG. In this study, an actively loaded open-bed compost filter, designed for the treatment of diluted LFG, was tested at an old landfill in Denmark. An 18 m3 biofilter was constructed in a 30 m3 container loaded with LFG mixed with air, in order to obtain diluted LFG. The inlet concentration of methane (CH4) fluctuated between 4.4 and 9.2 vol% during the five tested flow campaigns, resulting in CH4 loads of 106–794 g CH4 m−2 d−1. The maximum identified CH4 oxidation rate was 460 g m−2 d−1, with an overall CH4 oxidation efficiency of 58%. Due to preferential flows, especially along the edges of the filter at the transition points between the compost and the container wall, an overall CH4 oxidation efficiency of 100% was never achieved. However, pore gas profiles in selected areas in the filter material showed oxidation efficiencies close to 100%. The results were supported by tracer gas tests showing average oxidation efficiency in the nine measuring points of 89% at a CH4 load of 487 ± 64 g CH4 m−2 d−1.

Method Development for Container Closure Integrity Evaluation via Headspace Gas Ingress by Using Frequency Modulation Spectroscopy.

USP <1207.1> Section 3.5 states that "A deterministic leak test method having the ability to detect leaks at the product's maximum allowable leakage limit is preferred when establishing the inherent integrity of a container-closure system." Ideally, container closure integrity of parenteral packaging would be evaluated by measuring a physical property that is sensitive to the presence of any package defect that breaches package integrity by increasing its leakage above its maximum allowable leakage limit. The primary goals of the work presented herein were to demonstrate the viability of the nondestructive, deterministic method known as laser-based gas headspace analysis for evaluating container closure integrity and to provide a physical model for predicting leak rates for a variety of container volumes, headspace conditions, and defect sizes. The results demonstrate that laser-based headspace analysis provides sensitive, accurate, and reproducible measurements of the gas ingress into glass vial-stopper package assemblies that are under either diffusive or effusive leak conditions. Two different types of positive controls were examined. First, laser-drilled micro-holes in thin metal disks that were crimped on top of 15R glass vials served as positive controls with a well-characterized defect geometry. For these, a strong correlation was observed between the measured ingress parameter and the size of the defect for both diffusive and effusive conditions. Second, laser-drilled holes in the wall of glass vials served as controls that more closely simulate real-world defects. Due to their complex defect geometries, their diffusive and effusive ingress parameters did not necessarily correlate; this is an important observation that has significant implications for standardizing the characterization of container defects. Regardless, laser-based headspace analysis could readily differentiate positive and negative controls for all leak conditions, and the results provide a guide for method development of container closure integrity tests.LAY ABSTRACT: The new USP 39 <1207>, "Package Integrity Evaluation-Sterile Products", states in section 3.4.1: "tracer gas tests performed using … laser-based gas headspace analysis [have] been shown to be sensitive enough to quantitatively analyze leakage through the smallest leak paths found to pose the smallest chance of liquid leakage or microbial ingress in rigid packaging." In addition, USP <1207> also states that "for such methods, the limit of detection can be mathematically predicted on the basis of gas flow kinetics." Using the above statements as a foundation, this paper presents a theoretical basis for predicting the gas ingress through well-defined defects in product vials sealed under a variety of headspace conditions. These calculated predictions were experimentally validated by comparing them to measurements of changes in the headspace oxygen content or total pressure for several different positive controls using laser-based headspace analysis. The results demonstrated that laser-based headspace analysis can, by readily differentiating between negative controls and positive controls with a range of defect sizes on the micron scale, be used to assess container closure integrity. The work also demontrated that caution must be used when attempting to correlate a leak rate to an idealized defect-size parameter.

An integrated approach to study of strata behaviour and gas flow dynamics and its application

This paper presents an advanced and integrated research approach to longwall mining-induced strata movement, stress changes, fractures, and gas flow dynamics with actual examples of its application from recent studies for co-extraction of coal and methane development at Huainan Mining Group in China, in a deep and multi-seam mining environment. The advanced approach takes advantage of the latest techniques in Australia for mine scale geotechnical characterisation, field measurement, monitoring and numerical modelling. Key techniques described in this paper include coal mine site 3D geotechnical characterisation methods, surface deep downhole multi-point extensometers and piezometers for overburden displacement and pore pressure measurements during mining, tracer gas tests for goaf gas flow patterns, and advanced numerical modelling codes for coupled coal mine strata, water and gas simulations, and longwall goaf gas flow investigations. This integrated approach has resulted in significant insights into the complex dynamic interaction between strata, groundwater, and gas during mining at Huainan Mining Group in recent years. Based on the findings from the extensive field monitoring and numerical modelling studies, a three-dimensional annular-shaped overlying zone along the perimeter of the longwall panel was identified for optimal methane drainage during mining.

Contaminant transport in membrane based energy recovery ventilators

Ventilation systems are used to exhaust stale air and bring fresh air into sealed buildings. To maintain a comfortable indoor environment, this incoming air must be heated or cooled, which consumes energy. Consequently, membrane-based plate-type energy recovery ventilators are a component used in many energy-efficient ventilation systems. In these air-to-air energy recovery ventilator exchangers, incoming and outgoing air streams are passed over opposing sides of a membrane through which heat and moisture are transferred. This decreases the energy use of buildings by using the exhaust air to heat/cool and humidify/dehumidify the incoming air depending on the season. Ideally, membranes for these devices should have high water vapor permeation rates and be selective for water vapor over the transport of other gases and volatile organic compounds, including formaldehyde, odors, and contaminants, that may be present in the outgoing indoor air stream. Current certification and standards for contaminant crossover in North America focus on the measurement of the exhaust air transfer ratio based on tracer gas tests. This study demonstrates that although this test may be appropriate for measuring defects and leakage in exchangers, it may not account for all sorption and permeation phenomena that may be observed in polymeric membrane systems. Results are reported for the transport of water vapor, carbon dioxide, oxygen, and volatile organic compounds through a number of energy recovery ventilator membranes based on different polymers. Building ventilation systems are modeled using CONTAM software to demonstrate the effect of crossover through the energy recovery ventilator on indoor air quality under intermittent release (i.e., cooking odors, smoking, cleaning, etc.) and consistent release (i.e., off-gassing of volatile organic compounds or carbon dioxide associated with building materials or occupancy) of contaminants. It is shown that moderate crossover leakage in energy recovery ventilators should have minimal overall impact on indoor air quality in ventilated buildings.

Evaluation of Engineering Controls for the Mixing Of Flavorings Containing Diacetyl and other Volatile Ingredients

Exposures to diacetyl, a primary ingredient of butter flavoring, have been shown to cause respiratory disease among workers who mix flavorings. This study focused on evaluating ventilation controls designed to reduce emissions from the flavor mixing tanks, the major source of diacetyl in the plants. Five exhaust hood configurations were evaluated in the laboratory: standard hinged lid-opened, standard hinged lid-closed, hinged lid-slotted, dome with 38-mm gap, and dome with 114-mm gap. Tracer gas tests were performed to evaluate quantitative capture efficiency for each hood. A perforated copper coil was used to simulate an area source within the 1.2-meter diameter mixing tank. Capture efficiencies were measured at four hood exhaust flow rates (2.83, 5.66, 11.3, and 17.0 cubic meters per min) and three cross draft velocities (0, 30, and 60 meters per min). All hoods evaluated performed well with capture efficiencies above 90% for most combinations of exhaust volume and cross drafts. The standard hinged lid was the least expensive to manufacture and had the best average capture efficiency (over 99%) in the closed configuration for all exhaust flow rates and cross drafts. The hinged lid-slotted hood had some of the lowest capture efficiencies at the low exhaust flow rates compared to the other hood designs. The standard hinged lid performed well, even in the open position, and it provided a flexible approach to controlling emissions from mixing tanks. The dome hood gave results comparable to the standard hinged lid but it is more expensive to manufacture. The results of the study indicate that emissions from mixing tanks used in the production of flavorings can be controlled using simple inexpensive exhaust hoods.

The Evaluation of Bitumen Fume Capture Efficiency for Road Pavers

INRS has evaluated the performance of fume extraction systems on road pavement asphalt pavers over a two year period between 2009 and 2011. These systems are used to reduce operator exposure by capturing fumes at the auger, where most emissions are generated, and discharging them above the paver at sufficient velocity to prevent fumes blowing back towards the operator cab. Evaluation was conducted using a tracer gas (SF6), based on the NIOSH-proposed protocol (1997). Initial tests revealed the limits of this methodology, which included adverse effects on measurement resulting from the paver being located in a test hall; panelling installed to isolate the machine from draughts seriously distorted the flow field. Further tracer gas tests conducted outside, under conditions more representative of real operation, showed that the fume capture system must be integrated into the machine design. Special attention should be given when implementing various cooling systems (diesel engine, hydraulic compressor) since air draughts from these, if improperly directed, may greatly degrade fume capture efficiency.

Secondhand smoke transfer and reductions by air sealing and ventilation in multiunit buildings: PFT and nicotine verification

Surveys suggest that transfer of secondhand smoke (SHS) between units in multiunit residential buildings is common, but measured data are rare. This study was undertaken to quantify bulk air transfer between units and document transfer of SHS species before and after treatments that sealed boundaries between units and provided a minimum amount of continuous exhaust ventilation of each unit. Six buildings in Minnesota were studied. Treatments were performed in clusters of up to eight units in each building, including zero to two units occupied by smokers. Bulk air transfer was quantified through passive perfluorocarbon tracer (PFT) gas tests. SHS transfer was evaluated using passive nicotine sampling. The median fraction of air entering a unit that came from other units tagged with PFTs ranged from 0.021 in a new condominium building to 0.353 in a 1930s duplex, with an overall median of 0.041. Treatments provided a median decrease of 29% in the fraction of transferred air and reduced PFT concentrations by about 40%, because of increased ventilation of both source and target apartments. Nicotine was transferred at only one-sixth the rate of PFTs. Involuntary exposure to SHS can be reduced but not eliminated by modifying existing, occupied multiunit buildings. Recent studies of secondhand smoke exposure in multiunit housing indicate transmission of SHS constituents from smokers' units to those occupied by nonsmokers. A straightforward solution for this problem is to eliminate air leakage transfer between these units. This study describes a 2-year investigation of air sealing and ventilation improvements in six multiunit buildings located in a heating-dominated climate region of the US. The results quantify the reduction in interunit transfer of air between smokers' and nonsmokers' units. While it is possible to reduce the transfer when done with care, it is extremely difficult to eliminate these flows unless the buildings are vacated and extensively rebuilt. Eliminating air leakage between smokers' and nonsmokers' units is not a practical means of solving SHS transmission in an existing building.

Evaluation of the Alberta air infiltration model using measurements and inter-model comparisons

The Alberta air infiltration model (AIM-2) is a simplified single-zone model for predicting building air infiltration rates with a number of salient features. This paper presents an empirical study of this model using measured data from 16 detached houses in Ottawa, Canada. A single-fan depressurization test was first conducted for each house to determine its leakage characteristics. Then, the tracer gas concentration decay technique was employed to measure air infiltration rates under a wide range of weather conditions. The AIM-2 model was used to predict air infiltration rates for each of the 16 houses for the measured weather conditions. These model predictions were then compared with the air infiltration rates determined with the tracer gas tests. Additionally, the predictions of the AIM-2 model were compared with those of another model, the Lawrence Berkeley Laboratory (LBL) model. The AIM-2 model tended to underestimate air infiltration rates but performed better than the LBL model. On average, the AIM-2 model has an error of 19% while the LBL model has an error of 25%. The AIM-2 model requires an estimation of the house's leakage distribution, which may have contributed to some of this disagreement. An attempt was made to use genetic algorithms to reduce the uncertainty caused by estimating these model inputs.

Effects of wind on the transmission heat loss in duo-pitched insulated roofs: A field study

This article presents measuring results of the thermal performance of duo-pitched tiled woodframe roof designs. The roofs have been monitored in a test building, exposed to the outside climate. The experiment was part of a programme to study the hygrothermal performance of highly insulated envelope parts in situ, in order to investigate whether a good thermal quality ( U = 0.2 W/(m 2 K)) is achievable with current residential construction practices in Belgium. The results show the effect of wind on the thermal performance of duo-pitched roofs. The measured thermal properties of the roof components are compared to the design values, and related to the wind speeds and directions registered near the test building. The established thermal effects are explained using tracer gas tests to show the pattern of wind driven air flow in the roofs.

Effects of Sash Movement and Walk-bys on Aerodynamics and Contaminant Leakage of Laboratory Fume Cupboards

In order to speculate the physical mechanisms of contaminant leakage during sash movement and walk-bys through a laboratory fume cupboard, the complicated three-dimensional flow patterns and the real-time tracer gas leakage are studied via the laser-assisted flow visualization method and the standard gas sampling technique, respectively, over a transparent, full scale chemical fume cupboard. Through the flow visualization, the evolution of drastic changes of the flow pattern is demonstrated. The highly turbulent jet-like currents are induced by the unsteady flow motion near the cupboard face. Large-scale turbulent eddies accompanied with the jet-like currents obviously bring large amount of in-cupboard smoke out to the atmosphere. The turbulent mixing extends the size and the strength of the large-scale eddy circulations, and predominantly contributes to the mechanism that causes the severe spread of contaminant leakage in few seconds. The tracer gas tests that are conducted by employing pr-EN 14175:2003 method show consistent containment results with the flow visualization findings. The temporally evolving large-scale turbulent eddies induced by the sash movement and the walk-bys cause substantially high contaminant leakage to the environment and the breathing zone of the operator.

Aerodynamics and Performance Verifications of Test Methods for Laboratory Fume Cupboards

The laser-light-sheet-assisted smoke flow visualization technique is performed on a full-size, transparent, commercial grade chemical fume cupboard to diagnose the flow characteristics and to verify the validity of several current containment test methods. The visualized flow patterns identify the recirculation areas that would inevitably exist in the conventional fume cupboards because of the fundamental configurations and structures. The large-scale vortex structures exist around the side walls, the doorsill of the cupboard and in the vicinity of the near-wake region of the manikin. The identified recirculation areas are taken as the 'dangerous' regions where the risk of turbulent dispersion of contaminants may be high. Several existing tracer gas containment test methods (BS 7258:1994, prEN 14175-3:2003 and ANSI/ASHRAE 110:1995) are conducted to verify the effectiveness of these methods in detecting the contaminant leakage. By comparing the results of the flow visualization and the tracer gas tests, it is found that the local recirculation regions are more prone to contaminant leakage because of the complex interaction between the shear layers and the smoke movement through the mechanism of turbulent dispersion. From the point of view of aerodynamics, the present study verifies that the methodology of the prEN 14175-3:2003 protocol can produce more reliable and consistent results because it is based on the region-by-region measurement and encompasses the most area of the entire recirculation zone of the cupboard. A modified test method combined with the region-by-region approach at the presence of the manikin shows substantially different results of the containment. A better performance test method which can describe an operator's exposure and the correlation between flow characteristics and the contaminant leakage properties is therefore suggested.

Containment testing of laboratory hoods in the as-used condition.

Airborne contaminants generated inside laboratory fume hoods during use leak into the breathing zone of the user. Concentration of the leakage is unknown and variable depending on laboratory design, work practices, arrangement of internal apparatus, face velocity, and sash height. Surrogate tracer gas tests have been developed using sulfur hexafluoride (SF6) and a manikin to estimate leakage. This study presents results of hood leakage tests using SF6 with a manikin and then a live operator performing a phenol:chloroform (P:C) extraction. Four hoods were tested in each of three institutions during normal work hours with the lab occupied. The purpose of the study was to determine leakage concentrations for the SF6-manikin with effects of sash height, hood contents as found and after being cleaned out, face velocity, and the actual P:C and SF6 exposure concentrations of the user during work. Results indicate P:C was not detectable in the breathing zone of the 12 operators (< 0.1 ppm) at their selected operating sash heights (7 to 15 inches). Simultaneous SF6 concentrations were also minimal (average 0.06 ppm). Average leakage was 0.02 percent for SF6 and less than 2 percent based on chloroform concentrations measured in the breathing zone of the operator and inside the hood. SF6 percent leakage was greater when sash height was above the breathing zone of the manikin (average 2.09 percent) and lower leakage (average 0.02 percent) when below the breathing zone (26 inches or less). Average face velocity did not appear to be a predictor of average hood leakage. Cleaning out the hoods did not reduce leakage in most tests. The data from this study shows that when providing training on proper work practices for lab hood use, lowering the sash should be stressed as being the major factor in reducing hood leakage.

Application of a tracer gas challenge with a human subject to investigate factors affecting the performance of laboratory fume hoods.

The results of a "user" tracer gas test were applied to investigate the effects of various parameters on hood containment ability and to evaluate accepted methods to classify hood performance. This user tracer gas test was performed with a human subject standing in front of the hood. Based on the data collected, face velocity, its variability, and cross drafts are important in determining hood leakage. Results indicate that the temporal variability of face velocity may deserve as much consideration as its spatial variability, a parameter more traditionally recognized as being important. The data collected indicate that hoods with horizontally sliding sash doors perform better with the doors positioned to provide a center opening rather than when all of the doors are pushed to one side. The observed smoke patterns suggest that this trend is caused by the location and instability of vortices formed along the perimeter edge when all doors are pushed to one side. The results of manikin tracer gas tests and the user tracer gas test are inconsistent, suggesting that more research is needed to determine how best to evaluate whether a hood protects its users.