Outward Leakage Research Articles

Total outward leakage of face-worn products used by the general public for source control

During Coronavirus disease 2019 pandemic, the general public used any face-worn products they could get to overcome the shortage of N95 respirators and surgical masks. These products, often not meeting any standards, raised concerns about their effectiveness in reducing the spread of respiratory viruses. This study quantified total outward leakage (TOL) of units from 9 face-worn product categories used by members of the general public. A benchtop system was devised to test 2 units from each category on 2 different-sized headforms with silicone elastomer skin. Each unit was donned 5 times per headform. Both face-worn product category and headform size significantly affected TOL (Pvalue < .05). The TOL of tested face-worn products varied from 10% to 58% depending on both model and headform size. Face-worn products donned on the medium headform had a higher mean TOL compared to those donned on the larger headform. Overall, single-layer cloth masks are the least effective measure for source control due to their highest TOL among the tested face-worn products. Three-layer disposable face masks may be a favorable option for source control among the public. A standard should be developed for face-worn product design and manufacturing to accommodate different facial sizes.

Effect of Anderson localization on surface plasmon polariton propagation and outward leakage when scattered by a randomly corrugated section of the interface

Effect of Anderson localization on surface plasmon polariton propagation and outward leakage when scattered by a randomly corrugated section of the interface

Enhancing the Stability of Perovskite Solar Cells with a Multilayer Thin-Film Barrier

The long-term stability of perovskite solar cells (PSCs) remains a big challenge for the commercialization of this emerging photovoltaic technique. The protection of PSCs with a robust barrier/encapsulation could largely extend their life span. Here, we develop a multilayer thin-film barrier with the architecture of parylene/MgF2/Al2O3 as thin-film encapsulation for PSCs. The water vapor transmission rate of the multiple thin-film barriers can reach a very low value of 1 × 10–4 g m–2 d–1, comparable to that of the thin-film encapsulation in electronic packaging, making the multilayer thin-film barrier robust to block the ingress of H2O/O2 and outward leakage of perovskite decomposition byproducts. As a result, the light and thermal stability of perovskite films and the operational stability of PSCs are effectively improved with multiple thin-film barriers; especially, the encapsulated devices show negligible degradation after operation under the maximum power point tracking under 1sun illumination for 1000 h. In addition, the devices can retain 96% of their initial PCEs on average after aging for 100 h in an 85 °C-85%RH damp heat test.

Cloth face mask fit and function for children part two: Material Selection

The second component of this three-paper series studying cloth face masks for children ages 4 to 6 years old concentrates on optimizing aerosol capture and air permeability through fabric selection. Material choices were evaluated in two modes: Flat Filter (FF) and Head Form (HF). FF isolates material factors while HF simulates the performance of the constructed masks on a 3D printed child head form. In FF mode, higher filtration efficiency correlated to lower air permeability in both reusable commercial and experimental face masks regardless of fiber contents, fabric structures, and number of layers. Our prototype face mask developed in design exploration successfully captured 37 ± 12% of 0.3 μm, 87 ± 3% of 0.5 μm, and 87 ± 2% of 1.0 μm particles while maintaining good air permeability, moisture capture, and aerosolized salt capture in HF mode. Sealing masks to minimize outward leakage reduced particle capture up to 64%. Particle leakage data captured at the eye level of the head form illuminated the synergy between mask design, material choice, and fit.

Inhibitory Effect of Polypeptides Produced by Brevibacillus brevis on Ochratoxigenic Fungi in the Process of Pile-Fermentation of Post-Fermented Tea

Contamination by ochratoxigenic fungi and its prevention during the pile-fermentation of post-fermented tea have always been a concern. The present study aimed to elucidate the anti-fungal effect and mechanism of polypeptides produced by B. brevis DTM05 (isolated from post-fermented tea) on ochratoxigenic fungi, and to to evaluate their use in the pile-fermentation process of post-fermented tea. The results showed that polypeptides (produced by B. brevis DTM05) with a strong antifungal effect against A. carbonarius H9 mainly had a molecular weight between 3 and 5 kDa. The Fourier-transform infrared spectra of this polypeptide extract showed that it was a mixture consisting mainly of polypeptides and small amounts of lipids and other carbohydrates. The polypeptide extracts significantly inhibited the growth of A. carbonarius H9, and its minimum inhibitory concentration (MIC) was 1.6 mg/L, which significantly reduced the survival rate of spores. The polypeptides also effectively controlled the occurrence and ochratoxin A (OTA) production of A. carbonarius H9 on the tea matrix. The lowest concentration of polypeptides that significantly inhibited the growth of A. carbonarius H9 on the tea matrix was 3.2 mg/L. The enhancement of the fluorescence staining signal in the mycelium and conidiospore showed that the polypeptides with a concentration of more than 1.6 mg/L increased the permeability of the mycelium membrane and conidial membrane of A. carbonarius H9. The significant increase in the extracellular conductivity of mycelia suggested the outward leakage of intracellular active substances, and also further indicated an increase in cell membrane permeability. Polypeptides with a concentration of 6.4 mg/L significantly down-regulated the expression level of the polyketide synthase gene related to OTA production (acpks) in A. carbonarius H9, which may be the fundamental reason why polypeptides affect OTA production. In conclusion, reasonable use of the polypeptides produced by B. brevis can destroy the structural integrity of the cell membrane, make the intracellular active substances leak outward, accelerate the death of fungal cells and down-regulate the expression level of the polyketide synthase gene in A. carbonarius; thus, they can effectively control the contamination of ochratoxigenic fungi and OTA production during the pile-fermentation of the post-fermented tea.

Feature, Barrier Face Coverings for Workers.

Face coverings have been recommended for the public and workers to prevent person-to-person transmission of COVID-19. Throughout 2020, guidelines for face coverings recommended multiple layers worn tightly against the face with straps or ear loops. This article briefly describes a new ASTM 3502 Standard Specification for Barrier Face Coverings (BFCs) and the development of performance criteria for workplace BFCs ahead of the Occupational Safety and Health Administration (OSHA) COVID-19 Emergency Temporary Standards (ETS). We also describe a method for comparing the effect on the time to receipt of an infectious dose (ID) of BFCs with varying degrees of inward leakage (personal protection) and outward leakage (source control). The role of BFCs in workplace settings during the pandemic and for exposure to infectious respiratory organisms after the pandemic remains in question. It will be important for occupational health and safety professionals to recognize their limitations in contrast with respiratory protection.

A Simple Method to Quantify Outward Leakage of Medical Face Masks and Barrier Face Coverings: Implication for the Overall Filtration Efficiency.

Face masking proved essential to reduce transmission of COVID-19 and other respiratory infections in indoor environments, but standards and literature do not provide simple quantitative methods for quantifying air leakage at the face seal. This study reports an original method to quantify outward leakage and how wearing style impacts on leaks and filtration efficiency. The amount of air leakage was evaluated on four medical masks and four barrier face coverings, exploiting a theoretical model and an instrumented dummy head in a range of airflows between 30 and 160 L/min. The fraction of air leaking at the face seal of the medical masks and barrier face coverings ranged from 43% to 95% of exhaled air at 30 L/min and reduced to 10–85% at 160 L/min. Filter breathability was the main driver affecting both leak fraction and total filtration efficiency that varied from 5% to 53% and from 15% to 84% at 30 and 160 L/min, respectively. Minor changes were related to wearing style, supporting indications on the correct mask use. The fraction of air leaking from medical masks and barrier face coverings during exhalation is relevant and varies according to design and wearing style. The use of highly breathable filter materials reduces air leaks and improve total filtration efficiency.

Testing of outward leakage of different types of masks with a breathing manikin head, ultraviolet light and coloured water mist

ABSTRACT Since the outbreak of COVID-19, wearing a mask, voluntary or obligatory, has led to diverse and numerous designs. Guidelines for minimum requirements include tests for visual inspection, strength, filtration, and breathing resistance, but not for the fit of a mask. The fit of a mask was assessed by testing the outward leakage of exhaled breath based on the visualization of coloured mist exhaled by a manikin head. Fourteen masks were selected based on differences in design, such as type of material, shape (cheek wings vs. none), filter type, and the number of layers. Leakage expressed in mean mist percentages (visualized with a camera), patterns of coloured mist left inside the masks, as well as visual fit of the masks on the manikin head, showed that a loose fit mask results in more leakage. Also, combining quantitative with qualitative assessment proved to be complementary. Future tests should be conducted on a range of users, covering the best fit over time as well breathability, use, and comfort. The use of face masks, whatever their characteristics, seem an adequate strategy to reduce the dispersion of potential ‘infected’ aerosols into the space from people, as opposed to not wearing one.

Technical note: Impact of face covering on aerosol transport patterns during coughing and sneezing

COVID-19 is spread via different routes, including virus-laden airborne particles generated by human respiratory activities. In addition to large droplets, coughing and sneezing produce a lot of small aerosol particles. While face coverings are believed to reduce the aerosol transmission, information about their outward effectiveness is limited. Here, we determined the aerosol concentration patterns around a coughing and sneezing manikin and established spatial zones representing specific elevations of the aerosol concentration relative to the background. Real-time measurements of sub-micrometer aerosol particles were performed in the vicinity of the manikin. The tests were carried out without any face covering and with three different types of face covers: a safety faceshield, low-efficiency facemask and high-efficiency surgical mask. With no face covering, the simulated coughing and sneezing created a powerful forward-propagating fine aerosol flow. At 6 ft forward from the manikin head, the aerosol concentration was still 20-fold above the background. Adding a face covering reconfigured the forward-directed aerosol transmission pattern. The tested face coverings were found capable of mitigating the risk of coronavirus transmission; their effectiveness is dependent on the protective device. The outward leakage associated with a specific face covering was shown to be a major determinant of the exposure level for a person standing or seating next to or behind the coughing or sneezing “spreader” in a bus/train/aircraft/auditorium setting. Along with reports recently published in the literature, the study findings help assess the infectious dose and ultimately health risk for persons located within a 6-ft radius around the “spreader.”

Optimized design of thermal insulation and fluid drag reduction for circumferentially grooved annular seal with MMA and perturbation methods

Circumferentially grooved seals have been widely used in pumps to eliminate outward leakage of rotating liquid. On many occasions, the turbulent flow enhances the drag force on the interface between the liquid and the stator as well as the interface between the liquid and the rotor, creating much higher heat exchange than the conventional thermal conduction in laminar flows. Attention must be paid in the seal design to prevent rapid heating by the seal liquid to the ambient stator. In this study, the geometry of a circumferentially grooved seal is optimized for a better design of thermal insulation as well as reduction in drag force of the seal fluid. For the forward problem, i.e., the hydraulic and thermal analysis of the seal, the theory of bulk flow is used to simplify the thin-film liquid to a two-dimensional field which preserves the average characteristics of the original flow. The method of three-control volume is adopted to partition the liquid into three types of cavity flows. The governing equations of continuity, momentum, and energy transportation are presented for each control volume, and are approximated by the perturbation method and the Fourier expansion. The fluid and thermal solutions by the present perturbation method are validated by a CFD simulation. For the seal optimization, the multi-objective optimization for thermal insulation and drag reduction is converted into an integrated optimization problem with key geometrical parameters of the seal. Response surfaces are generated through radial basis functions to make the constraint functions explicit for the efficiency of the optimization process. The method of moving asymptotes (MMA) is adopted to find the optimized design of the seal geometry with the best performance of thermal insulation and drag reduction of liquid. Examples are presented to demonstrate the effectiveness of the present optimization method.

COMPUTATIONAL FLUID DYNAMICS SIMULATION OF FLOW OF EXHALED PARTICLES FROM POWERED-AIR PURIFYING RESPIRATORS.

In surgical settings, infectious particulate wound contamination is a recognized cause of post-operative infections. Powered air-purifying respirators (PAPRs) are widely used by healthcare workers personal protection against infectious aerosols. Healthcare infection preventionists have expressed concern about the possibility that infectious particles expelled from PAPR exhalation channels could lead to healthcare associated infections, especially in operative settings where sterile procedural technique is emphasized. This study used computational fluid dynamics (CFD) modeling to simulate and visualize the distribution of particles exhaled by the PAPR wearer. In CFD simulations, the outward release of the exhaled particles, i.e., ratio of exhaled particle concentration outside the PAPR to that of inside the PAPR, was determined. This study also evaluated the effect of particle sizes, supplied air flow rates, and breathing work rates on outward leakage. This simulation study for the headform and loose-fitting PAPR system included the following four main steps: (1) preprocessing (establishing a geometrical model of a headform wearing a loose-fitting PAPR by capturing a 3D image), (2) defining a mathematical model for the headform and PAPR system, and (3) running a total 24 simulations with four particle sizes, three breathing workloads and two supplied-air flow rates (4×3×2=24) applied on the digital model of the headform and PAPR system, and (4) post-processing the simulation results to visually display the distribution of exhaled particles inside the PAPR and determine the particle concentration of outside the PAPR compared with the concentration inside. We assume that there was no ambient particle, and only exhaled particles existed. The results showed that the ratio of the exhaled particle concentration outside to inside the PAPR were influenced by exhaled particle sizes, breathing workloads, and supplied-air flow rates. We found that outward concentration leakage from PAPR wearers was approximately 9% with a particle size of 0.1 and 1 μm at the light breathing and 205 L/min supplied-air flow rates, which is similar to the respiratory physiology of a health care worker in operative settings, The range of the ratio of exhaled particle concentration leaking outside the PAPR to the exhaled particle concentration inside the PAPR is from 7.6% to 49. We found that supplied air flow rates and work rates have significant impact on outward leakage, the outward concentration leakage increased as particle size decreased, breathing workload increased, and supplied-air flow rate decreased. The results of our simulation study should help provide a foundation for future clinical studies.

The Influence of Air Gap Thickness between the Stator and Rotor on Nuclear Main Pump

The canned motor pumps are commonly used as main umps in nuclear primary circuit systems, because the typically outward leakage clearance in general centrifugal pumps does not exist in the canned motor pumps. The longer air gap thickness between the motor stator and the rotor, the more cooling liquid flowing through the air gap, which results the heat exchange becomes better between the motor and the cooling liquid and the temperature rise of the motor is lower. These are all good for improving the motor efficiency at the angle of the view, the temperature rise. From another angle of the view, the electromagnetism, the longer thickness between the motor stator and the rotor, the weaker interaction between the stator and rotor magnetic fields, which results the Lorentz force becomes weaker and the torque becomes smaller, and also the motor efficiency becomes lower. Therefore, there is an optimum value of the air gap thickness between the stator and the rotor, to balance the temperature rise and the electromagnetism interaction. In this paper with the case of 30kW canned motor, the coupled analysis of the heat exchange and the electromagnetic performance was studied. The influence of the air gap thickness on the motor temperature rise and on the electromagnetic performance was discussed respectively, and then the optimum value of the air gap thickness was given.

WE-FG-206-03: An Adaptive Model for Pharmacokinetic Nested Model Selection in Dynamic Contrast Enhanced MRI Data Analysis

Purpose: This study introduces an adaptive Model Selection (MS) technique to perform Pharmacokinetic nested MS from the time trace of longitudinal relaxation rate change, ΔR1 (R1 = 1/T1) in Dynamic Contrast Enhanced (DCE) MRI studies. Methods: Three physiologically nested models derived from the standard Tofts model along with an averaged (over 30 patients) arterial input function were used to simulate a set of ΔR1 profiles to describe possible physiological conditions of underlying tissue pathology: Model-1: the vascular compartment is filled with contrast agent (CA) with no outward leakage. Model-2: the vascular compartment is filled with CA with outward leakage but no evidence of back-flux. Model-3: the vascular compartment is filled with CA with both outward and backward-flux. Three different sets of simulated ΔR1 profiles in presence of different signal-to-noise ratios (5, 10, 15, 30, 70, 100, and no noise) were used to train an Artificial Neural Network (ANN) for performing MS. A k-fold cross-validation method was used to validate and optimize the ANN architecture. The trained-ANN was also applied on the DCE-MRI data of 20 patients with Glioblastoma and results were compared to the models selected by the Log-Likelihood-Ratio (LLR) technique using Dice coefficient. Results: The confusion matrix and the strong similarity (Dice coefficients of 0.87, 0.89 for Models 2 and 3) between the models selected by the trained ANN and the LLR method confirms that the performance of the adaptive NMS technique is superior to the LLR method. The ANN showed a strong sensitivity for selecting models with higher orders; thus less type-II errors (never misses any tissues with leaky vasculature (Models 2 and 3). Conclusion: The noise insensitivity, speed, and superiority of the ANN technique in choosing the best PK model would allow a less biased estimation of cerebrovascular permeability parameters in tumorous tissues. This work is supported in part by HFHS mentored Grant (A10237).

A working hypothesis about the cause of Be stars: Episodic outward leakage of low-frequency waves excited by the iron-peak κ-mechanism

AbstractObservations indicate that a circumstellar disk is formed around a Be star while the stellar rotation is below the break-up velocity. I propose a working hypothesis to explain this mystery by taking account of the effect of leaky waves upon angular momentum transfer.In B-type stars near the main sequence, low-frequency nonradial oscillations are excited by the κ-mechanism in the iron bump. They transport angular momentum from the driving zone to the surface. As a consequence, the angular momentum is gradually deposited near the stellar surface. This results in a gradual increase in the “critical frequency for g-modes”, and g-modes eventually start to leak outward, long before the surface rotation reaches the break-up velocity. This leads to a substantial amount of angular momentum loss from the star, and a circumstellar disk is formed. The oscillations themselves will be soon damped owing to kinetic energy loss. Then the envelope of the star spins down and angular momentum loss stops soon. The star returns to being quiet and remains calm until nonradial oscillations are newly built up by the κ-mechanism to sufficient amplitude and a new episode begins.According to this view, the interval of episodic Be-star activity corresponds to the growth time of the oscillation, and it seems in good agreement with observations.

Involvement of inwardly rectifying K+ channels in secretory responses of human ileal mucosa.

In acute secretory diarrhoea the primary event driving fluid secretion is a transcellular, electrogenic, serosal to mucosal transport of chloride ions. Such transport requires the maintenance of an electrically negative cell membrane voltage, which is achieved through a basolateral outward leakage of potassium ions. The aim of this study was to investigate the nature of K(+) channel involvement in facilitating secretory processes in the human ileum. Muscle-stripped mucosal preparations of human ileal mucosa were set up in Ussing chambers for recording short-circuit current and transmucosal conductance. Escherichia coli heat-stable toxin and vasoactive intestinal peptide (VIP) produced concentration-dependent increases in short-circuit current. Responses to the heat-stable toxin were unaffected by basolateral application of 4-aminopyridine (5 mM), glibenclamide (10 microM) or a combination of charybdotoxin (0.3 microM) plus apamin (0.3 microM). However, basolateral barium (0.2-5 mM) caused a concentration-dependent inhibition. Responses to VIP were similarly affected by barium (0.05-1 mM). These results suggested that electrogenic chloride transport by human ileal mucosa required the presence of basolateral K(+) channels. The use of selective K(+)-channel inhibitors and low concentrations of barium suggested that the channels involved might be of the inwardly rectifying type.

Catecholamine Metabolism: A Contemporary View with Implications for Physiology and Medicine

This article provides an update about catecholamine metabolism, with emphasis on correcting common misconceptions relevant to catecholamine systems in health and disease. Importantly, most metabolism of catecholamines takes place within the same cells where the amines are synthesized. This mainly occurs secondary to leakage of catecholamines from vesicular stores into the cytoplasm. These stores exist in a highly dynamic equilibrium, with passive outward leakage counterbalanced by inward active transport controlled by vesicular monoamine transporters. In catecholaminergic neurons, the presence of monoamine oxidase leads to formation of reactive catecholaldehydes. Production of these toxic aldehydes depends on the dynamics of vesicular-axoplasmic monoamine exchange and enzyme-catalyzed conversion to nontoxic acids or alcohols. In sympathetic nerves, the aldehyde produced from norepinephrine is converted to 3,4-dihydroxyphenylglycol, not 3,4-dihydroxymandelic acid. Subsequent extraneuronal O-methylation consequently leads to production of 3-methoxy-4-hydroxyphenylglycol, not vanillylmandelic acid. Vanillylmandelic acid is instead formed in the liver by oxidation of 3-methoxy-4-hydroxyphenylglycol catalyzed by alcohol and aldehyde dehydrogenases. Compared to intraneuronal deamination, extraneuronal O-methylation of norepinephrine and epinephrine to metanephrines represent minor pathways of metabolism. The single largest source of metanephrines is the adrenal medulla. Similarly, pheochromocytoma tumor cells produce large amounts of metanephrines from catecholamines leaking from stores. Thus, these metabolites are particularly useful for detecting pheochromocytomas. The large contribution of intraneuronal deamination to catecholamine turnover, and dependence of this on the vesicular-axoplasmic monoamine exchange process, helps explain how synthesis, release, metabolism, turnover, and stores of catecholamines are regulated in a coordinated fashion during stress and in disease states.

Leaky catecholamine stores: undue waste or a stress response coping mechanism?

Turnover of catecholamines, representing the constant loss and replenishment of neurotransmitter by synthesis, is usually considered to be driven exclusively by catecholamine release. This is incorrect. An important contribution of intraneuronal metabolism of norepinephrine to turnover, and dependence of this on leakage of norepinephrine from vesicular stores, was originally proposed by Kopin in 1964. Several years later, Maas and colleagues concluded that at least 75% of norepinephrine turnover is due to intraneuronal metabolism without prior release at sympathetic nerve endings. More recently it was shown in the resting human heart that about 12% of norepinephrine turnover is due to extraneuronal uptake and metabolism or loss of the transmitter to the circulation, 15% is due to intraneuronal metabolism after reuptake, and 73% is due to intraneuronal metabolism of norepinephrine leaking from storage vesicles. Thus, contrary to usual depictions, vesicular stores of catecholamines do not exist in a static state simply waiting for exocytotic release. Rather, these stores exist in a highly dynamic equilibrium with the surrounding cytoplasm, with passive outward leakage of amines counterbalanced by inward active transport under the control of vesicular monoamine transporters. The large contribution of leakage to catecholamine turnover may seem inconsistent with cellular economy. In fact, this contribution provides an important mechanism for "gearing down" the requirement for increases in catecholamine synthesis to match increases in catecholamine release, and thereby provides sympathetic nerves with a capacity for a more extended range of sustainable release rates in response to stress than would otherwise be possible.

Safety design for ITER and fusion power reactors

The present paper outlines key design features of relevance for the safety of international thermonuclear experimental reactor (ITER) and fusion devices of reactor scale. These features support the intrinsic safety characteristics of fusion. The most important safety function is the confinement of radioactivity. The first barrier is based on the vacuum vessel (VV) and its extensions. A pressure suppression system limits the maximum pressure of the VV in the event of loss of coolant. The second barrier is the Cryostat and its extensions. Outward leakage from the second confinement can be captured in surrounding rooms where necessary. Open penetrations of the VV will be protected by at least two separate barriers such as windows or valves. Nuclear decay heat will be removed passively by the VV cooling system. Other safety systems have been identified which play an important role for both ITER and a fusion power reactor.

Required response time for variable air volume fume hood controllers

This paper describes results from tests made with the aim of investigating how quickly the exhaust air flow rate through fume hoods needs to be controlled in order to prevent contaminants from leaking out of the fume hood and putting the safety of the laboratory personnel at risk. The measurements were made on a laboratory fume hood in a chemical laboratory. There were no other fume hoods in the laboratory, and the measurements were made without interference from persons entering or leaving the laboratory or walking about in it. A tracer gas method was used with the concentration of dinitrogen oxide (N(2)O) being recorded by a Foxboro Miran 101 infra-red gas analyser. In parallel with the tracer gas measurements, the air velocity through the face opening was also measured, as was the control signal to the damper controlling the air flow rate. The measurements show an increased outward leakage of tracer gas from the fume hood if the air flow rate is not re-established within 1-2 s after the sash is opened. If the delay exceeds 3 s the safety function is temporarily defeated. The measurements were made under virtually ideal conditions. Under more typical conditions, the fume hood could be exposed to various other external perturbations, which means that the control system should re-establish the correct exhaust flow more quickly than indicated by the measurement results obtained under these almost ideal conditions.

Required response time for variable air volume fume hood controllers

This paper describes results from tests made with the aim of investigating how quickly the exhaust air flow rate through fume hoods needs to be controlled in order to prevent contaminants from leaking out of the fume hood and putting the safety of the laboratory personnel at risk. The measurements were made on a laboratory fume hood in a chemical laboratory. There were no other fume hoods in the laboratory, and the measurements were made without interference from persons entering or leaving the laboratory or walking about in it. A tracer gas method was used with the concentration of dinitrogen oxide (N2O) being recorded by a Foxboro Miran 101 infra-red gas analyser. In parallel with the tracer gas measurements, the air velocity through the face opening was also measured, as was the control signal to the damper controlling the air flow rate. The measurements show an increased outward leakage of tracer gas from the fume hood if the air flow rate is not re-established within 1–2 s after the sash is opened. If the delay exceeds 3 s the safety function is temporarily defeated. The measurements were made under virtually ideal conditions. Under more typical conditions, the fume hood could be exposed to various other external perturbations, which means that the control system should re-establish the correct exhaust flow more quickly than indicated by the measurement results obtained under these almost ideal conditions.