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Conventional drying of spices, as hot air treatment, often needs an additional downstream inactivation step to decrease the microbial load of the dried product and improve its microbial safety and microbial quality. In this regard, the present work explored the possibility to dry and decontaminate food in a single step using supercritical carbon dioxide (scCO2) as a drying agent. A case study was focused on the drying of herbs and the antimicrobial effects were evaluated on the naturally present microbiota. For this purpose, experiments were carried out on coriander leaves using a high pressure vessel at 10 MPa, at two different temperatures (40 and 50°C) with drying time of 0 and 150 min to establish the influence of each parameter on the microbial inactivation. Yeasts and molds appeared to be the least resistant to scCO2 as they could never be detected after the treatment (

Ultraviolet germicidal irradiation of cooling coils controls biofouling that increases airflow resistance and decreases heat transfer coefficient. Though lower in power than air disinfection systems, coil ultraviolet germicidal irradiation systems should provide some collateral air treatment benefit. This benefit is estimated through monetization of simulated nonfatal illness spread in a group of commercial buildings. Benefits were quantified using appropriate metrics for each building type: work-loss days for office buildings, hospital acquired infections for healthcare facilities, and disability adjusted life years for schools. The pre-ultraviolet germicidal irradiation annual cost of occupant illness was the same order of magnitude as annual energy cost. Area-normalized cost was similar in magnitude for all buildings. The collateral air disinfection of coil surface ultraviolet germicidal irradiation reduced baseline illness costs by 3.5% or less, but the resulting cost savings exceeded the energy cost ...

Pumice is a valuable scouring, scrubbing, and polishing material both in powdered form and as a pumice stone. It has been traditionally used in construction industry and biomedicine. It has been evaluated in recent years in the field of water, wastewater, and air treatment. The present study aimed to review the scientific literature of pumice stone with the particular focus on its use for the treatment of water and wastewater. It was observed that most of the publications from 1995 to 2015 dealt with construction materials and treatment use. A number of 143 papers published focused on the removal of cadmium, dyes, color, and many other pollutants by adsorption and catalytic oxidation, while 49% of the papers on water and wastewater treatment was dedicated on adsorption processes. Besides, pumice has been used as a filter medium and integrated to biological treatment. More recent publications have been focusing on integrating pumice with advanced oxidation processes (AOPs) after enrichment with oth...

SummaryGarlic (Allium sativum L.) is a clonally propagated crop that can be infected by many virus species which tend to accumulate year-after-year, leading to yield reductions and varietal degeneration. Therefore, the production and use of virus-free planting material is vital to sustain productivity. In this study, Onion yellow dwarf virus (OYDV; Potyvirus), Garlic common latent virus (GarCLV; Carlavirus), Shallot latent virus (SLV; Carlavirus), and Garlic virus X (GarV-X; Allexivirus) were detected in cloves of the commercial garlic cultivar, ‘G-1’ (‘Jamuna Safed’) by direct antigen-coated enzyme-linked immunosorbent assay (DAC-ELISA). DAC-ELISA was performed using specific antisera against each virus species, and confirmed through reverse transcription-polymerase chain reactions (RT-PCR) using virus or genus-specific oligonucleotide primers. To obtain virus-free plants of ‘G-1’, cloves were subjected to solar heat treatment for 5, 10, or 15 d, or to hot air treatment (at 37°C, 40°C, or 42°C for 7, 14,...

To determine the effect of gamma irradiation, steaming and heating on microbial load and chemical composition of licorice root powder.Powders were exposed to hot air treatment at 60°C for 24 h, steaming at 1.1 bar and about 121°C for 15 min, and irradiation at 10 kGy using a (60)Co source. Microbial load, moisture, ash, and electrical conductivity (EC) values of licorice root powders were evaluated immediately after treatment, and after 12 months of storage.Total aerobic plate count (TAPC) of licorice roots powder (control sample), including coliform, Escherichia coli, and Klebsiella spp. were relatively high. Irradiation reduced the TAPC by 4 logs and total coliform to negative (less than 1 log(10) colony forming units (CFU) g(-1)) Klebsiella spp., E. coli, and Salmonella spp. were not detected (less than 1 log(10) CFU/g) in irradiated sample. Meanwhile, heating and steaming reduced the total count by 1 and 2 logs with slight effect on reducing the total coliforms counts. Also, irradiated samples were free of coliforms. No considerable changes in the moisture and ash were observed in irradiated powders, but the moisture increased due to steaming, and decreased due to dried heating.Gamma irradiation at 10 kGy was more effective than heating and steaming treatments in their microbial decontamination effect on the licorice root powders.

Changes in the number and species diversity of cultivable microorganisms in a newly developed plate-type biofilter during filtration of various volatile pollutants were studied. The novelty of the investigation is the monitoring of microorganism succession in different parts of biofilter plates with original packing material consisting of birch fibre and needle-punched non-woven fabric. It was shown that the largest number of fungi and yeasts develop on the top and middle, while bacteria develop on the bottom and middle parts of plates. The number of microorganisms depends on the origin of the pollutant, the pH and temperature inside the biofilter and the moisture of the porous plates. The statistically significant correlation between the number of microorganisms and inlet concentration of acetone was estimated, while ammonia showed a negative influence on yeast distribution. Paecilomyces variotii, Rhodotorula mucilaginosa and Bacillus subtilis were the most common organisms found during filtration of all examined volatiles; however, some differences of microbial communities in different parts of the biofilter plates and filtrated volatile compounds were obtained.

Most developing and developed countries are facing the problems and challenges of air pollution. Many governments have enacted laws and policies to enforce industrial activities to reduce air contaminating emissions and are mainly carried out by installation of air pollution control systems. Therefore, the use of suitable technique such as biofiltration processes to control air pollutants is necessary. Although many studies have been published on the designing and operations of polluted air treatment using biofiltration processes but a comprehensive review on it is still lacking. Till now due to conceptual designing and operational knowledge, several cases of failure or sub-optimum designing has been reported about the use of biofiltration process to treat polluted air. This paper presents a comprehensive review of biofiltration processes and technology for the control of organic and inorganic pollutants as an ideal approach to remove pollutants from polluted air. It also covers classification, fu...

Mitigation of bioaerosol emissions from concentrated animal feeding operations (CAFOs) demands knowledge of bioaerosol concentrations feeding into an end-of-pipe air treatment process. The aim of this preliminary study was to measure total endotoxin and (1 --> 3)-beta-glucan concentrations at the air exhaust of 18 commercial CAFOs and to examine their variability with animal operation type (swine farrowing, swine gestation, swine weaning, swine finishing, manure belt laying hen, and tom turkey) and season (cold, mild, and hot). The measured airborne concentrations of total endotoxin ranged from 98 to 23,157 endotoxin units (EU)/m3, and the airborne concentrations of total (1 --> 3)-beta-D-glucan ranged from 2.4 to 537.9 ng/m3. Animal operation type in this study had a significant effect on airborne concentrations of total endotoxin and (1 --> 3)-beta-D-glucan but no significant effect on their concentrations in total suspended particulate (TSP). Both endotoxin and (1 --> 3)-beta-D-glucan attained their highest airborne concentrations in visited tom turkey buildings. Comparatively, season had no significant effect on airborne concentrations of total endotoxin or (1 --> 3)-beta-D-glucan. Endotoxin and (1 --> 3)-beta-glucan concentrations in TSP dust appeared to increase as the weather became warmer, and this seasonal effect was significant in swine buildings. Elevated indoor temperatures in the hot season were considered to facilitate the growth and propagation of bacteria and fungi, thus leading to higher biocomponent concentrations in TSP.

Photocatalytic oxidation (PCO) is a promising technology for indoor air purification due to low operating cost, potentially long service life, and low maintenance. Ultraviolet light-emitting diode (UVLED) is a new concept in the field of PCO, which has several advantages over conventional UV light sources. Limited research has been conducted using UVLED PCO for air treatment. This study demonstrated the potential application of UVLED for the removal of volatile organic compounds (VOCs; toluene and xylene) from indoor air under different operating conditions including flow rate (25-117 cubic feet per minute [cfm]), types of catalysts (Degussa P25, sol-gel TiO2, nitrogen-doped TiO2, clay TiO2, and Bi2O3), LED intensity, and humidity in a continuous reactor. About 7-32% VOC removal occurred depending on the experimental conditions. The results show that UVLED can activate different types of photocatalysts effectively.This study demonstrates the effectiveness of UVLED in photocatalytic oxidation applied for indoor air cleaning. Several TiO2 catalysts (Degussa P25, sol-gel TiO2, nitrogen-doped TiO2, clay TiO2, and Bi2O3) were used in the reactor to characterize the removal performance of indoor air pollutants, for example, VOCs. This is one of the very few studies that have, to date, examined toluene and xylene removal from indoor air using these catalysts with UVLED in a continuous reactor. The intent is to develop an energy-efficient continuous reaction system to remove VOCs from indoor air. The performance of the system was characterized with respect to air flow rate, humidity, types of catalysts, and light intensity.

With the development of the new Swiss Ventafresh technology (Steffen, 2007; Steffen et al., 2007a,b) that produces edible, packaged foods having much longer shelf-lives than are available by current technologies, new vistas in food service and restaurant service have become available. About 170 km outside of Madrid is a new food processing and packaging plant. Raw foodstuffs (spices, fruits, meats, vegetables, rice, potatoes, pasta, salads, etc.) are delivered to this plant where they are washed (in ozone-containing water), peeled, sliced, etc. Microwaveable packing trays are filled with ingredients of a complete meal and then sealed with a microwaveable plastic film (sometimes with modified atmospheres). Both the packing trays and the sealing film are disinfected using combinations of ozone and UV radiation. Individual meals are prepared and packaged, but are not precooked, then are delivered to five (currently) Crono Chef restaurants strategically located throughout Madrid (www.crono.tv). There are only...

A novel air dehumidifier using HCOOK solution has experimentally been tested to be feasible and effective. Air flow rate and its relative humidity have big impacts on air dehumidification. The decrease of relative humidity could be over 25% using a strong HCOOK solution to desiccate highly humid air (>75% RH). However, it does not dehumidify efficiently the air with a relative humidity lower than 43% even if strong HCOOK desiccant solution is used. In highly humid spaces, such as bathroom, swimming pool, or kitchen, air dehumidification using a liquid desiccant is very efficient.

Summary‘Qingnai’ plums are popular as “green” fruit throughout south-east Asia. However, the fruit soften rapidly after harvest, limiting commercial exports from China. Traditionally, the crop is sold mostly to the local population. We evaluated the potential of hot-air treatment (HAT) to delay ripening of ‘Qingnai’ plum fruit as a potential technology to expand the marketing of “green” plums. Fruit were stored at 20°C after being exposed to 20°C (control), 40°C (HAT40), 45°C (HAT45), or 50°C (HAT50) air for 5 h. Information was collected on fruit firmness, peel colour, chlorophyll contents, chlorophyllase activities, soluble solids contents (SSC), titratable acidities (TA), the rates of respiration and ethylene production, and the activities of cell wall hydrolysing enzymes. Fruit softening was accompanied by a progressive decrease in hue angle (h°), chlorophyll content, and TA, and increases in chlorophyllase, pectin methylesterase (PME) and polygalacturonase (PG) activities. Hot-air treatment delayed t...

This project evaluated the effects of exposing a variety of microorganisms on porous and non-porous materials to elevated gaseous ozone concentrations ranging from 100 – 1000 ppm. Gypsum wallboard (porous) and glass slide (non-porous) building materials were used. Two fungi organisms, two bacteria organisms and two levels of relative humidity (RH) were tested. Increased humidity and non-porous surface exposure were found to increase the biocidal capability of high levels of ozone. The results of this study indicate that even at relatively high concentrations of ozone, it is difficult to get significant reductions of microorganisms on surfaces, especially on porous materials.

This work studies the economic feasibility of integrating a rotary solid desiccant wheel with the conventional vapor compression air-conditioning system in the city of Beirut. To increase the economic practicality of such a hybrid system, the combined system utilizes the heat dissipated by the condenser and natural gas heat energy in regenerating the desiccant wheel. A heat and mass transfer desiccant model is developed to study the hourly performance of the hybrid system when used in air conditioning a typical auditorium (150 m2) over the entire cooling season. The economic performance of the hybrid system is compared with the conventional air-conditioning system while varying the number of occupants in the auditorium from 10 to 100 to change the sensible heat ratio from 0.53 to 0.27 and the percentage of the outside fresh air from 25% to 100%. The conventional system cooling load range was between 9.2 kW and 63.4 kW for the cases simulated in this work, while the vapor compression subsystem varied in th...

Antibiotics can be present in low concentrations in domestic wastewater, but little is known about their effect on bacteria in onsite wastewater treatment systems. Mesocosms, consisting of soil-filled lysimeters representing the leachfield of a septic system under aerated (AIR) and unaerated (LEACH) conditions, were used to study the effects of tetracycline addition (5 mg L(-1)) to septic tank effluent on tetracycline resistance in the fecal indicator bacteria Escherichia coli and fecal streptococci, and on their removal. The mesocosms were dosed with antibiotic for 10 days, and effects monitored for 52 days. The fraction of resistant bacteria in mesocosm drainage water relative to that in septic tank effluent, GammaRes, for E. coli ranged from 0 to 0.66 in the AIR treatment and from 0 to 3.32 in the LEACH treatment. For fecal streptococci, GammaRes ranged from 0 to 0.41 and from 0.63 to 1.06 in the AIR and LEACH treatments, respectively. No significant differences in antibiotic resistance of fecal indicator bacteria were observed among sampling dates in soil or water from either treatment. Tetracycline had no significant effect on removal of fecal indicator bacteria, which ranged from 99.9 to 100% for E. coli and from 95.9 to 100% for fecal streptococci. Our results suggest that short-term addition of tetracycline at environmentally-relevant concentrations is likely to have minimal consequences on pathogen removal from wastewater and development of antibiotic resistance among pathogenic bacteria in leachfield soil.

Ozone has the strongest oxidization effect after fluorine, and this property has been used in sterilization for food and processing plants in Japan. Moreover, there is no fear of toxic residues as with chlorine-based sterilizers and no hazardous trihalomethanes are formed. Based on these advantages, ozone has been used in water and air treatment for food products food materials and food processing plants. Use in the food processing is now increasing in Japan. This paper describes ozone sterilization, introducing sterilization systems and equipment applied to food in Japan.

An enclosed flow-through system using airborne ozone for disinfection and which removes the ozone with a catalytic converter was tested with a strain of Escherichia coli. Petri dishes containing the microorganisms were inserted in a chamber and exposed for 10-480 min to ozone concentrations between 4 and 20 ppm. Death rates in excess of 99.99% were achieved. Survival data is fitted to a two-stage curve with a shoulder based on the multihit target model. Ozone was removed from the exhaust air to nondetectable levels using a metal oxide based catalyst. The possibility of using ozone as an airborne disinfectant for internal building surfaces and catalytically removing the ozone on exhaust is demonstrated to be feasible. A model for the decay of Bacillus cereus under ozone exposure is proposed as an example for predicting the sterilization of buildings contaminated with anthrax. The potential for disinfecting airstreams and removing ozone to create breathable air is also implied by the results of this experiment.

The main purpose of the present work is to acquire further insight into the procedure of heat and mass transfer between sprayed water droplets and air stream in a direct evaporative air cooler used in air-conditioning systems in textile mills. The thermodynamic models of the two-phase flow in such an air treatment system have been developed for both the one row parallel flow spray and one row counter flow spray. The fields of temperature and relative humidity in the spray chamber have been obtained by calcula-tion. A series of experiments aimed at quantifying the system performance and its influence factors have been conducted. This indicates that the increases of air velocity and water/air ratio, together with the decrease of nozzle density are favorable. Comparison of these two different spray types have been carried out by means of humidity efficiency. Finally, numerical calculations have been compared with experimental results. Satisfactory agreements have been found regarding outlet air temperature while a maximum error of 10% has been observed regarding relative air humidity.

As we enter this new century, it is striking how the number of applications for ozone is growing. During ozone's first century, the emphasis for using it involved primarily, potable water treatment, wastewater treatment, bottled water treatment, odor control and medical therapy. Of these, potable water and wastewater treatment now can be called the “classical” applications for ozone. But there are a great many more uses for this versatile chemical that might be termed “non-classical”, and these began emerging toward the end of the last century. Some of these so-called “non-classical” developing applications for ozone will be reviewed in this paper. As we enter the 21s1 century, applications for ozone in the various aspects of the agricultural and food processing industries are very active and most promising.

It has been reported that highly adsorptive granular activated carbon improves the biofilter performance. In this work the effect of adsorption property of the medium, on the biofilter capacity of eliminating organic components in waste gas streams is theoretically discussed using a biofilter model. In this first paper adsorption capacity is assumed to be in excess and steady-state solutions are compared with Ottengraf's solutions in various limiting situations. When first-order kinetics is used in the substrate utilization rate, as the value of α increases, the corresponding values of the dimensionless pollutant concentration in a biofilm and the dimensionless pollutant concentration in waste-gas streams through a biofilter become lower at a given value of Thiele modulus, through the thickness of the biofilm and the height of the biofilter, respectively. However, the effect of α becomes insignificant when the value of Thiele modulus becomes larger than a certain number. With zero order kinetics in the substrate utilization rate, for both situations of reaction limiting and diffusion limiting, their steady-state solutions are obtained.

The design and the construction of an actual 8.7-m3 pilot/full-scale biotrickling filter for waste air treatment is described and compared with a previous conceptual scale-up of a laboratory reactor. The reactor construction costs are detailed and show that about one-half of the total reactor costs ($97,000 out of $178,000) was for personnel and engineering time, whereas approximately 20% was for monitoring and control equipment. A detailed treatment cost analysis demonstrated that, for an empty bed contact time of 90 sec, the overall treatment costs (including capital charges) were as low as $8.7/1000 m3air in the case where a nonchlorinated volatile organic compound (VOC) was treated, and $14/1000 m3air for chlorinated compounds such as CH2Cl2. Comparison of these costs with conventional air pollution control techniques demonstrates excellent perspectives for more field applications of biotrickling filters. As the specific costs of building and operating biotrickling filter reactors decrease with increasing size of the reactor, the cost benefit of biotrickling filtration is expected to increase for full technical-scale bioreactors.

A new concept of periodically rotating biotrickling filters was developed for parallel operation of multiple bench scale biotrickling filters without the requirement for expensive equipment such as liquid recycle pumps and air flow regulation. The performance of 20 identically operated rotating biotrickling filters was reproducible with an average toluene elimination capacity of 79.4 g m−3 h−1 (s.d. = 5.7) at an empty bed residence time of 45 s and a toluene inlet gas phase concentration of 1.6 g m−3. At gas and liquid cocurrent operation, the toluene elimination capacity of rotating biotrickling filters was 20% higher than at countercurrent operation. This was probably caused by greater mass transfer limitation resulting from increased wetting of the biofilm during countercurrent operation. Performance versus load curves of rotating and of conventional biotrickling filters were comparable with non-zero order removal at toluene inlet concentrations lower than 2 g m−3. This multiple rotating biotrickling f...

The purpose of this experimental study was to determine if corona-enhanced chemical vapor deposition of silicone found in personal care products can cause silicon-oxide to grow on the discharge wires of electrostatic air cleaners. To test the hypothesis, a wire-cylinder precipitator was operated with a positive corona discharge for 180 hours with an air/octamethylcyclotetrasiloxane mixture. The 30.5 cm-long precipitator has a 200 μm-diameter tungsten wire suspended in a 3.3 cm-diameter aluminum tube. The silicone, called cyclomethicone in product ingredient lists, is commonly found in deodorants, hair care products, lotions, and cosmetics, and it is volatile at room temperature. Experiments were conducted at current and voltage levels typical of the charging section of commercial indoor air cleaners. Concentration of the cyclomethicone vapor was approximately 1000 ppm. Results confirm that the presence of this silicone vapor in positive corona discharge creates amorphous silicon-oxide deposits on...

Soybean (Glycine max L. Merr.) cultivars Akisirome and Peking were inoculated with Bradyrhizobium japonicum Is-21 and Rhizobium fredii USDA 194, respectively, and were grown in cylindrical pots containing sterilized vermiculite which were aerated with CO2-free air or ambient air to study the effects of CO2 deficiency in the rhizosphere on plant growth, nodulation, and nitrogen fixation. The repressive effects of CO2-free air treatment were more conspicuous in Peking than Akisirome, and nodule number, nodule mass, amount of biologically fixed N and plant growth of Peking were reduced remarkably by the CO2-free air treatment. Acetylene reduction activity (ARA) of Peking inoculated with USDA 194 and Akisirome inoculated Is-21 was assayed in the absence and presence of CO2, ARA of Akisirome was not affected by the absence of CO2, while that of Peking decreased drastically. Based on these results, it was concluded that nitrogen fixation by Akisirome inoculated with B. japonicum Is-21 was not appreciab...

Laboratory scale biological trickling filters and three-phase airlift bioreactors have been studied for the elimination of methylene chloride (or dichloromethane) vapors from waste air, and the results used herein for the design of small industrial-scale reactors. The conditions chosen for scale-up were an air flow rate of 100 m3 h-1, a methylene chloride inlet concentration of 2 g m-3, and a target removal of 99.5%. The scale-up procedure, design, and cost analysis are discussed. The full-scale biotrickling filter appears to be the most cost-effective reactor, with global costs of about $62 per 1,000 m3 treated. Treatment in the airlift reactor was estimated to be twice as expensive and catalytic oxidation 5 times as expensive. Biological waste air treatment offers economical alternatives to conventional techniques for waste air treatment.

Concentrations of complexed and free cyanide were determined in manufactured gas plant (MGP) purifier waste samples collected from two MGP sites in New York State. Standard additions of NaCN gave total cyanide levels of 14.3 ± 1.0 and 23.6 ± 3.7 mg CN g‐1 DWT (oven dry weight of solids) for the two samples. Free cyanide in both samples was less than the method detection limit. Accordingly, the cyanide values cited pertain to cyanide in complexes; these complexes are expected to be largely inorganic. A second determination on Sample 2 using standard addition of complexed rather than free cyanide yielded 25.8 ± 3.2 mg CN g‐1 DWT. From these data, it appears that gas purifier wastes may be expected to contain as much as 1 to 3 percent cyanide as CN on a dry weight basis.

The removal of gaseous iodine from air by water sprays is measured, using both ordinary water and a solution buffered to a pH near 9.5 with a carbonate mixture. The results are compared to the theo...

In spite of extensive research and development work illustrating the significant advantages of Electrically Stimulated Filters (ESF's), this technology has not been commercially successful. This paper addresses this subject by analyzing conventional filter and ESF cost effectiveness in HEFA, clean room and indoor air cleaning applications. A new cost effective form of ESF technology has been considered: a single (charging and collection) field device. The laboratory performance of five commercially available conventional filters and the new ESF is characterized in terms of efficiency versus particle size, flow rate versus pressure drop and dirt loading characteristics. Using this information and the application requirements, the cost effectiveness of the ESF has been established with respect to conventional filters. Both initial and operating costs are discussed. The results show that ESF technology is cost effective for indoor applications even where space constraints are not important. Space co...

Removal of H2S, CH3SH and (CH3)3N, mixed with air in a concentration range from 10 to 800 ppm at 303 K, by use of activated carbon impregnated with NaOH or Na2CO3 (IAC) or sulfonated activated carbon (SAC) was studied to obtain the basic data useful for design of a deodorization process. For the system of IAC-H2S or CH3SH, the adsorption equilibrium was of rectangular type and adsorption capacity could be increased as much as about 40 to 60 times of that of original carbon. For the system of SAC-(CH3)3N, the adsorption equilibrium obeyed the Freundlich equation and the effect of sulfonation was much larger when the concentration of (CH3)3N was lower in comparison with the original carbon. Intraparticle effective diffusivity, Dic or Diq, was determined by curve-fitting of calculated breakthrough curves with experimental ones. The value of Dic or Diq decreased with the increase of the amount impregnated or the amount of acidic functional groups (-SO3H and -COOH) introduced by sulfonation.

The protection provided by carbon-containing organic vapor respirator cartridges depends in part on the packing density of the carbon in the cartridges and its degree of activation. Large variations in these parameters could have significant effects on the service-life of respirator cartridges. Variability among commercially available organic vapor respirator cartridges was examined with regard to the following characteristics: the particle size distribution, amount of carbon and packing density of the carbon in the cartridges and the degree of activation of the carbon. The degree of activation was determined by measuring the maximum adsorption space and the structural constant of the carbon. These two parameters--Wo (cm3/g) and k (cal/M)-2--are constants in the Dubinin/Radushkevich (D/R) model from which physical absorption onto microporous adsorbents, such as activated carbon, are described. Respirator cartridges from three different suppliers were examined. Significant variability (11-40%) in the amount and the degree of activation of the carbon occurred between cartridges of different manufacturers, as well as among cartridges of an individual manufacturer.

A tracer gas technique using sulfur hexafluoride (SF6) was developed for the evaluation of industrial exhaust hood efficiency. In addition to other parameters, accuracy of this method depends on proper location of the sampling probe. The sampling probe should be located in the duct at a minimum distance from the investigated hood where the SF6 is dispersed uniformly across the duct cross section. To determine the minimum sampling distance, the SF6 dispersion in the duct in fully developed turbulent flow was studied at four duct configurations frequently found in industry: straight duct, straight duct-side branch, straight duct-one elbow, and straight duct-two elbows combinations. Based on the established SF6 dispersion factor, the minimum sampling distances were determined as follows: for straight duct, at least 50 duct diameters; for straight duct-side branch combination, at least 25 duct diameters; for straight duct-one elbow combination, 7 duct diameters; and for straight duct-two elbow combination, 4 duct diameters. Sampling at (or beyond) these distances minimizes the error caused by the non-homogeneous dispersion of SF6 in the duct and contributes to the accuracy of the tracer gas technique.

A study was conducted at a secondary lead smelter to evaluate the workplace performance of the 3M W-344 and Racal AH3 powered air-purifying respirators equipped with helmets and high efficiency filters. The research protocol developed for the study has been described in a companion paper. The results of the study indicate that the mean lead concentrations, measured inside the facepiece of both PAPRs, were significantly less than the OSHA lead exposure limit of 50 micrograms/m3. The means of the workplace protection factor measurements on both PAPRs were significantly less than the PAPR selection guide protection factor classification of 1000. Correlation analysis of preshift quantitative fit factors and corresponding workplace protection factors indicated no linear association between these two measures of performance. This finding suggests that for PAPRs equipped with helmets and high efficiency filters quantitative fit factors as presently determined are not indicative of the workplace protection which the respirators provide. Since the PAPR protection factor classification of 1000 was originally based on quantitative fit factors, the lack of a demonstrated association between quantitative fit factors and workplace protection as found in this study may explain why their performance was significantly less than expected.

An evaluation of the efficacy of household air cleaning devices as a means to control radon decay products in existing buildings is presented. Previous research on air cleaning methods for airborne radon decay products has been directed primarily to the control of radon decay products in mines and has only limited application to control in residences where dust concentration, air change rate, and humidity are lower than in mines. Results show that room size air cleaners can achieve substantial reductions in working levels in residences. Reductions observed at air infiltration rates of 0.52 air changes per hour ranged from 58 to 89%. Although the two air cleaners tested produced the greatest reductions, the low cost, simplicity, and other benefits of air circulating fans, particularly the ceiling fan, appear to make them most suitable for residences. (JMT)