Unvented Gas Research Articles

Indoor Exposure to Selected Air Pollutants in the Home Environment: A Systematic Review.

(1) Background: There is increasing awareness that the quality of the indoor environment affects our health and well-being. Indoor air quality (IAQ) in particular has an impact on multiple health outcomes, including respiratory and cardiovascular illness, allergic symptoms, cancers, and premature mortality. (2) Methods: We carried out a global systematic literature review on indoor exposure to selected air pollutants associated with adverse health effects, and related household characteristics, seasonal influences and occupancy patterns. We screened records from six bibliographic databases: ABI/INFORM, Environment s, Pollution s, PubMed, ProQuest Biological and Health Professional, and Scopus. (3) Results: Information on indoor exposure levels and determinants, emission sources, and associated health effects was extracted from 141 studies from 29 countries. The most-studied pollutants were particulate matter (PM2.5 and PM10); nitrogen dioxide (NO2); volatile organic compounds (VOCs) including benzene, toluene, xylenes and formaldehyde; and polycyclic aromatic hydrocarbons (PAHs) including naphthalene. Identified indoor PM2.5 sources include smoking, cooking, heating, use of incense, candles, and insecticides, while cleaning, housework, presence of pets and movement of people were the main sources of coarse particles. Outdoor air is a major PM2.5 source in rooms with natural ventilation in roadside households. Major sources of NO2 indoors are unvented gas heaters and cookers. Predictors of indoor NO2 are ventilation, season, and outdoor NO2 levels. VOCs are emitted from a wide range of indoor and outdoor sources, including smoking, solvent use, renovations, and household products. Formaldehyde levels are higher in newer houses and in the presence of new furniture, while PAH levels are higher in smoking households. High indoor particulate matter, NO2 and VOC levels were typically associated with respiratory symptoms, particularly asthma symptoms in children. (4) Conclusions: Household characteristics and occupant activities play a large role in indoor exposure, particularly cigarette smoking for PM2.5, gas appliances for NO2, and household products for VOCs and PAHs. Home location near high-traffic-density roads, redecoration, and small house size contribute to high indoor air pollution. In most studies, air exchange rates are negatively associated with indoor air pollution. These findings can inform interventions aiming to improve IAQ in residential properties in a variety of settings.

Keeping it Safe: Space Heaters

Each year, hundreds of people go to hospital emergency rooms because of injuries related to space heaters. When clothing comes in contact with a heating element or flame it can catch fire. Leaking gas can cause explosions. Inhaling carbon monoxide from a malfunctioning, poorly vented, or unvented gas heater can cause death. This document is FCS5233-02, one of a series of the Department of Family, Youth and Community Sciences, UF/IFAS Extension. Original publication date: May 2002. Revised: December 2005.

Probabilistic assessment of the potential indoor air impacts of vent-free gas heating appliances in energy-efficient homes in the United States

ABSTRACTUse of vent-free gas heating appliances for supplemental heating in U.S. homes is increasing. However, there is currently a lack of information on the potential impact of these appliances on indoor air quality for homes constructed according to energy-efficient and green building standards. A probabilistic analysis was conducted to estimate the impact of vent-free gas heating appliances on indoor air concentrations of carbon monoxide (CO), nitrogen dioxide (NO2), carbon dioxide (CO2), water vapor, and oxygen in “tight” energy-efficient homes in the United States. A total of 20,000 simulations were conducted for each Department of Energy (DOE) heating region to capture a wide range of home sizes, appliance features, and conditions, by varying a number of parameters, e.g., room volume, house volume, outdoor humidity, air exchange rates, appliance input rates (Btu/hr), and house heat loss factors. Predicted airborne levels of CO were below the U.S. Environmental Protection Agency (EPA) standard of 9 ppm for all modeled cases. The airborne concentrations of NO2 were below the U.S. Consumer Product Safety Commission (CPSC) guideline of 0.3 ppm and the Health Canada benchmark of 0.25 ppm in all cases and were below the World Health Organization (WHO) standard of 0.11 ppm in 99–100% of all cases. Predicted levels of CO2 were below the Health Canada standard of 3500 ppm for all simulated cases. Oxygen levels in the room of vent-free heating appliance use were not significantly reduced. The great majority of cases in all DOE regions were associated with relative humidity (RH) levels from all indoor water vapor sources that were less than the EPA-recommended 70% RH maximum to avoid active mold and mildew growth. The conclusion of this investigation is that when installed in accordance with the manufacturer’s instructions, vent-free gas heating appliances maintain acceptable indoor air quality in tight energy-efficient homes, as defined by the standards referenced in this report.Implications: Probabilistic modeling of indoor air concentrations of carbon monoxide (CO), nitrogen dioxide (NO2), carbon dioxide (CO2), water vapor, and oxygen associated with use of vent-free gas heating appliances provides new data indicating that uses of these devices are consistent with acceptable indoor air quality in “tight” energy-efficient homes in the United States. This study will provide authoritative bodies such as the International Code Council with definitive information that will assist in the development of future versions of national building codes, and will provide evaluation of the performance of unvented gas heating products in energy conservation homes.

Lung Cancer Risk from Radon in Marcellus Shale Gas in Northeast U.S. Homes.

The amount of radon in natural gas varies with its source. Little has been published about the radon from shale gas to date, making estimates of its impact on radon-induced lung cancer speculative. We measured radon in natural gas pipelines carrying gas from the Marcellus Shale in Pennsylvania and West Virginia. Radon concentrations ranged from 1,520 to 2,750 Bq/m3 (41-74 pCi/L), and the throughput-weighted average was 1,983 Bq/m3 (54 pCi/L). Potential radon exposure due to the use of Marcellus Shale gas for cooking and space heating using vent-free heaters or gas ranges in northeastern U.S. homes and apartments was assessed. Though the measured radon concentrations are higher than what has been previously reported, it is unlikely that exposure from natural gas cooking would exceed 1.2 Bq/m3 (<1% of the U.S. Environmental Protection Agency's action level). Using worst-case assumptions, we estimate the excess lifetime (70 years) lung cancer risk associated with cooking to be 1.8×10-4 (interval spanning 95% of simulation results: 8.5×10-5 , 3.4×10-4 ). The risk profile for supplemental heating with unvented gas appliances is similar. Individuals using unvented gas appliances to provide primary heating may face lifetime risks as high as 3.9×10-3 . Under current housing stock and gas consumption assumptions, expected levels of residential radon exposure due to unvented combustion of Marcellus Shale natural gas in the Northeast United States do not result in a detectable change in the lung cancer death rates.

Forensic Engineering Analysis of Unvented Gas Appliances in High Altitudes

A family moves into a house about 4,000 feet above sea level. They use a refrigerator powered by LP gas. A short time after the refrigerator was installed, they notice and complain about smells and soot. They take their 9-month-old to a hospital in response to persistent crying. A short time later, they notify the refrigerator manufacturer, which examines and tests the refrigerator. They find the refrigerator’s burner venturi blocked, generating high levels of carbon monoxide. Twelve years later, the parents bring a lawsuit against the installers of the refrigerator. At that time, the appliance is not available, and the house has been remodeled. A forensic engineering study is assigned to determine the effect high altitude has on this particular appliance design.

4種の拡散サンプラーを用いる札幌市における屋内外のガス状化学物質の実態調査

Gaseous chemical compounds such as carbonyls, volatile organic compounds (VOC), acid gases, basic gases, and ozone were measured in indoor and outdoor air of 40 houses throughout Sapporo city in the winter (January to March, 2012 and 2013) and summer (July to September, 2012) using four kinds of diffusive samplers. Almost all compounds in indoor air were present at higher levels in the summer than in the winter. The indoor concentrations of acetaldehyde and p-dichlorobenzene exceeded the Health, Labour and Welfare, Japan guideline in three and two houses, respectively. The mean concentrations of formaldehyde were 27 μg m−3 in the summer and 17 μg m−3 in the winter, and showed that the summer concentration was 1.6-fold higher than that in the winter. Nitrogen dioxide was present in extremely high concentrations in the winter, and it was suggested that the sources of nitrogen dioxide in indoor air are kerosene heaters, unvented gas stoves and heaters. Formic acid was generated by combustion because the nitrogen dioxide concentration in indoor air was well correlated with the formic acid concentration (correlation coefficient = 0.947). In outdoor air, the negative correlation between nitrogen dioxide and ozone was observed during the winter. It was suggested that the reaction of nitric oxide and ozone may influence the formation of nitrogen dioxide.

Home interventions are effective at decreasing indoor nitrogen dioxide concentrations

Nitrogen dioxide (NO2 ), a by-product of combustion produced by indoor gas appliances such as cooking stoves, is associated with respiratory symptoms in those with obstructive airways disease. We conducted a three-armed randomized trial to evaluate the efficacy of interventions aimed at reducing indoor NO2 concentrations in homes with unvented gas stoves: (i) replacement of existing gas stove with electric stove; (ii) installation of ventilation hood over existing gas stove; and (iii) placement of air purifiers with high-efficiency particulate air (HEPA) and carbon filters. Home inspection and NO2 monitoring were conducted at 1 week pre-intervention and at 1 week and 3 months post-intervention. Stove replacement resulted in a 51% and 42% decrease in median NO2 concentration at 3 months of follow-up in the kitchen and bedroom, respectively (P = 0.01, P = 0.01); air purifier placement resulted in an immediate decrease in median NO2 concentration in the kitchen (27%, P < 0.01) and bedroom (22%, P = 0.02), but at 3 months, a significant reduction was seen only in the kitchen (20%, P = 0.05). NO2 concentrations in the kitchen and bedroom did not significantly change following ventilation hood installation. Replacing unvented gas stoves with electric stoves or placement of air purifiers with HEPA and carbon filters can decrease indoor NO2 concentrations in urban homes. Several combustion sources unique to the residential indoor environment, including gas stoves, produce nitrogen dioxide (NO2), and higher NO2 concentrations, are associated with worse respiratory morbidity in people with obstructive lung disease. A handful of studies have modified the indoor environment by replacing unvented gas heaters; this study, to our knowledge, is the first randomized study to target unvented gas stoves. The results of this study show that simple home interventions, including replacement of an unvented gas stove with an electric stove or placement of HEPA air purifiers with carbon filters, can significantly decrease indoor NO2 concentrations.

Ultrafine particle concentrations and exposures in seven residences in northern California

Human exposures to ultrafine particles (UFP) are poorly characterized given the potential associated health risks. Residences are important sites of exposure. To characterize residential exposures to UFP in some circumstances and to investigate governing factors, seven single-family houses in California were studied during 2007-2009. During multiday periods, time-resolved particle number concentrations were monitored indoors and outdoors and information was acquired concerning occupancy, source-related activities, and building operation. On average, occupants were home for 70% of their time. The geometric mean time-average residential exposure concentration for 21 study subjects was 14,500 particles per cm(3) (GSD = 1.8; arithmetic mean ± standard deviation = 17,000 ± 10,300 particles per cm(3)). The average contribution to residential exposures from indoor episodic sources was 150% of the contribution from particles of outdoor origin. Unvented natural-gas pilot lights contributed up to 19% to exposure for the two households where present. Episodic indoor source activities, most notably cooking, caused the highest peak exposures and most of the variation in exposure among houses. Owing to the importance of indoor sources and variations in the infiltration factor, residential exposure to UFP cannot be characterized by ambient measurements alone. Indoor and outdoor sources each contribute to residential ultrafine particle (UFP) concentrations and exposures. Under the conditions investigated, peak exposure concentrations indoors were associated with cooking, using candles, or the use of a furnace. Active particle removal systems can mitigate exposure by reducing the persistence of particles indoors. Eliminating the use of unvented gas pilot lights on cooking appliances could also be beneficial. The study results indicate that characterization of human exposure to UFP, an air pollutant of emerging public health concern, cannot be accomplished without a good understanding of conditions inside residences.

Measured concentrations of combustion gases from the use of unvented gas fireplaces

Measurements of combustion product concentrations were taken in 30 homes where unvented gas fireplaces were used. Measurements of CO, CO(2), NO(x), NO(2) , O(2) (depletion), and water vapor were taken at 1-min interval. The analyzers were calibrated with certified calibration gases for each placement and were in operation for 3-4 days at each home. Measured concentrations were compared to published health-based standards and guidelines. The two combustion gases that exceeded published values were NO(2) and CO. For NO(2) , the Health Canada guideline of 250 ppb (1-h average) was exceeded in about 43% of the sample and the World Health Organization (WHO) guideline of 110 ppb (1-h average) was exceeded in 80% of the sample. Carbon monoxide levels exceeded the U.S. EPA 8-h average standard of 9 ppm in 20% of the sample. Moisture problems were not evident in the test homes. An analysis of the distribution of CO showed that the CO is dispersed throughout the home almost immediately upon operation of the fireplace and that the concentrations throughout the home away from the immediate vicinity of the fireplace are 70-80% of the level near the fireplace. Decay analysis of the combustion gases showed that NO was similarly stable to CO and CO(2) in the indoor environment but that both NO(2) and water vapor were removed from the air at much greater rates. Previous studies on unvented gas fireplaces have made assumptions of how they are operated by users. This article presents the results of field monitoring of 30 unvented gas fireplaces under normal operation, regardless of whether users follow industry recommendations regarding installation, usage patterns, and maintenance. The monitoring found that health-based standards and guidelines were exceeded for CO in 20% of homes and for NO(2) in most homes. There were no identified moisture problems in these homes. Nearly, half of the fireplaces were used at least once for longer than 2 h, counter to manufacturers' intended usage as supplemental heating. This demonstrates that given actual usage patterns and compared to current health-based thresholds, these appliances can produce indoor air concentrations considered to be unhealthy to at least sensitive or at-risk individuals.

아파트 실내 환경에서 실시간 측정시스템을 활용한 HONO 농도 측정 및 생성기작 연구

Nitrous acid (HONO) can be produced by heterogenous reactions of nitrogen dioxide on surface materials and direct emission from combustion sources. However, a little is known of indoor HONO levels or the relationship between residential HONO, NO, and <TEX>$NO_2$</TEX> concentrations in occupied houses. Therefore, we measured simultaneously NO, <TEX>$NO_2$</TEX>, and HONO concentrations in living room of an apartment using continuous analyzers to study the production of HONO (June <TEX>$22{\sim}30$</TEX>, 2006). The 4-min average concentrations of indoor NO, <TEX>$NO_2$</TEX>, and HONO were 4.3 (range: <TEX>$0.4{\sim}214.3$</TEX>), 10.3 (<TEX>$2.0{\sim}87.3$</TEX>), and 1.8 ppb (<TEX>$0.3{\sim}7.7$</TEX>), respectively. Peak levels of HONO up to 7.7 ppb and 24-hr averages as high as 1.7 ppb were measured. In agreement with previous studies, indoor HONO concentrations increased during operation of an unvented gas range. Examination of the observed kinetics suggests that the secondary production of indoor HONO, possibly as a result of heterogeneous reactions involving <TEX>$NO_2$</TEX> and <TEX>$H_2O$</TEX> is associated with <TEX>$[NO_2]^2[H_2O]\;(r^2=0.88)$</TEX> rather than with <TEX>$[NO][NO_2][H_2O]\;(r^2=0.75)$</TEX>. Three combustion experiments at nighttime were also carried out to investigate the effects of vented combustion on the HONO, NO, and <TEX>$NO_2$</TEX> concentrations. It was found to release HONO for <TEX>$10{\sim}15$</TEX> minutes after NO and <TEX>$NO_2$</TEX> source was turned off, and peak values were finally attained. Compared to unvented combustion, peak <TEX>$NO_2$</TEX> and HONO concentrations were 3.2 and 2.0 times lower at weak vented combustion (air flow: <TEX>$340\;m^3/hr$</TEX>) and 4.9 and 2.4 times lower at strong vented combustion (air flow: <TEX>$540\;m^3/hr$</TEX>), respectively, emphasizing importance of operating ventilation hood fan during combustion to improve indoor air quality.

TRAFFIC-RELATED AIR POLLUTION AND THE DEVELOPMENT OF ASTHMA, ALLERGY AND RESPIRATORY INFECTIONS: EXTENDED FOLLOW-UP OF A BIRTH COHORT

ISEE-134 Introduction: We have previously examined the relationship between traffic-related air pollution and the development of asthmatic/allergic symptoms and respiratory infections in the first two years of life for a birth cohort (N∼ 4,000) study in The Netherlands. Here we present findings from analysis at age four. Methods: A validated model based on measurements and geographic modeling was used to assign outdoor concentrations of traffic-related air pollutants (NO2, PM2.5 and “soot”) at the home addresses of the cohort. Questionnaire-derived data on wheeze, dry nighttime cough, ear/nose/throat infections, skin rash and physician diagnoses of asthma, bronchitis, influenza and eczema at age four were analyzed in relation to air pollutants. Multiple logistic regression models controlled for gender, maternal age, parental education, parental allergy, maternal smoking, ETS exposure, other siblings, ethnicity, breastfeeding, mattress cover, and the presence of mold, pets and unvented gas appliances at home. Total IgE and specific IgE to Der p1 (house dust mite), Der f1 (house dust mite), Fel d1 (cat), Can f1 (dog), grass pollen, birch pollen, egg, milk and Alternaria was measured in a subset (n∼ 700) of the cohort. Results: Adjusted odds ratios for wheeze (e.g., OR=1.8, 95% CI = 1.1–2.7 for “soot”), doctor-diagnosed asthma (2.2, 1.1–4.7), ear/nose/throat infections (1.7, 1.1–2.5) and flu/serious colds (1.8, 1.1–3.0) indicated positive associations with air pollutants. No consistent positive associations were observed for eczema, skin rash, cough or bronchitis. In the subset of the cohort with objective measurements of allergic sensitization (specific IgE), we also observed positive associations between air pollution and sensitization to food allergens (e.g., 5.6, 1.0–15.8 for “soot”), but no indications of associations with sensitization to indoor or outdoor aeroallergens or with elevated total IgE. As sensitization to food allergens (28%) was more prevalent than sensitization to indoor (17%) or outdoor (9%) allergens, further follow-up is necessary to determine if this sensitization shifts towards aeroallergens at later ages. Conclusion: These findings at age four confirm earlier observations made at age 2 in the same cohort and indicate associations between exposure to traffic-related air pollution and asthma, allergy and respiratory infections in a birth cohort.

Environmental factors

Environmental factors

Indoor Air Quality in Bulgaria

High temperature combustion is the main source of nitric oxide (NO) and nitrogen dioxide (NO2) in the air. Unvented gas and kerosene cooking appliances and space heaters are found to be the major indoor emission sources. It is important to know the level of exposure to NO2 in order to study their effects on health, to establish dose-effect relationships and to de vise appropriate pollution control strategies. Recognising these problems prompted a project which aimed to study the exposure to NO 2 among children aged 10-12 years living in 4 settlements in Bulgaria. The group of children investigated, whose parents included both smokers and non-smokers, came from homes with different types of heating and cooking appliances. The study was based on questionnaires-diaries. Palmes tubes were used for monitoring both personal exposure to NO2 and the levels indoors (kitchen, living room) and outdoors. The data obtained from the study showed that the concentra tions of NO2 were highest in homes which had gas cooking stoves and in which the parents were smokers.

Association of respiratory symptoms and lung function in young adults with use of domestic gas appliances

SummaryBackground There is evidence from some studies that people living in homes with gas stoves and other unvented gas appliances experience more respiratory symptoms than those who use other fuels for cooking and heating, but other studies have found no such association. We have investigated whether the use of gas appliances is associated with an increased risk of respiratory symptoms and whether sensitisation to common environmental allergens modifies any such association.Methods A stratified random sample of 15 000 adults aged 20-44 years, living in three towns in East Anglia, UK, were sent a questionnaire on asthma and hayfever. From those who responded, a random sample of 1864 were invited to complete an extended questionnaire that included questions on use of gas appliances, to give blood samples for measurements of total IgE and specific IgE to common allergens, and to undergo tests of respiratory function. 659 women and 500 men agreed to an interview. The association of the use of gas appliances with respiratory symptoms, total IgE, specific IgE, and respiratory function was assessed by logistic and multiple regression models.Findings Women who reported they mainly used gas for cooking had an increased risk of several asthma-like symptoms during the past 12 months including wheeze (odds ratio 2·07 [95% Cl 1·41-3·05]), waking with shortness of breath (2·32 [1·25-4·34]), and asthma attacks (2·60 [1·20-5·65]). Gas cooking increased the risk of symptoms more in women who were atopic than in non-atopic women but the difference did not reach significance (p>0·05). Women who used a gas stove or had an open gas fire had reduced lung function (forced expiratory volume in 1 s [FEV1]) and increased airways obstruction (FEV1 as a percentage of forced vital capacity) compared with women who did not. These associations were not observed in men.Interpretation In East Anglia, the use of gas cooking is significantly associated with subjective and objective markers of respiratory morbidity in women but not in men. Women may be more susceptible than men to the products of gas combustion or they may have greater exposure to high concentrations of these products because they cook more frequently than men.

Nitrogen Dioxide and Respiratory Illnesses in Infants

Nitrogen dioxide is an oxidant gas that contaminates outdoor air and indoor air in homes with unvented gas appliances. A prospective cohort study was carried out to test the hypothesis that residential exposure to NO2 increases incidence and severity of respiratory illnesses during the first 18 months of life. A cohort of 1,205 healthy infants from homes without smokers was enrolled. The daily occurrence of respiratory symptoms and illnesses was reported by the mothers every 2 wk. Illnesses with wheezing or wet cough were classified as lower respiratory tract. Indoor NO2 concentrations were serially measured with passive samplers place in the subjects' bedrooms. In stratified analyses, illness incidence rates did not consistently increase with exposure to NO2 or stove type. In multivariate analyses that adjusted for potential confounding factors, odds ratios were not significantly elevated for current or lagged NO2 exposures, or stove type. Illness duration, a measure of illness severity, was not associated with NO2 exposure. The findings can be extended to homes with gas stoves in regions of the United States where the outdoor air is not heavily polluted by NO2.

Buoyantly-driven two-phase countercurrent flow in liquid discharge from a vessel with an unvented gas space

This paper details experiments and analyses regarding the phenomenon of liquid discharge into a gaseous atmosphere from the bottom of a vessel with an unvented, upper gas space. The primary goal is the development of a simple model that predicts the rate of liquid discharge under the prevailing unvented condition. A literature survey of previous work on this phenomenon yielded only simple experiments and analyses that were limited in scope. Experiments were subsequently undertaken with an air-water system, using a larger volume and a wide range of drain line diameters. In addition to flowrate data, visual information was acquired regarding the physical mechanism possibly governing the prevalent flow regimes. The governing physical mechanism is identified as the stability of a gas-liquid interface, perturbed by buoyancy, at the drain line entrance. G.I. Taylor's fundamental analysis of interfacial stability lead to the determination of criteria for flow regime transition among the three prevalent flow regimes, corresponding to so-called small, medium, and large diameters. Also, analysis of the growth of interfacial instabilities lead to the application of flooding models for drainage rates within each regime. The models for moderate and large diameters were then compared against data, which confirmed their success in predicting discharge rates under the unvented condition. The motivation for this effort, besides the basic scientific significance of studying such a fundamental phenomenon, was its numerous applications, one of which is commercial nuclear reactor systems. Specifically, the phenomenon prevails in liquid coolant discharge from a PWR pressurizer, with an unvented steam volume, into a steam atmosphere existing in the adjoining hot coolant leg. Such a phenomenon could occur as part of a transient, or severe accident, scenario, entailing saturated conditions and steam production in the normally subcooled primary heat transport loop. The developed model was implemented in the Modular Accident Analysis Program (MAAP), a computer code designed to predict reactor system behavior in response to postulated off-normal conditions, including severe accident scenarios.

Pollutant Emission Rates from a Radiant Fiber-Matrix Gas Burner

Previous studies have quantified the emissions of trace constituents from unvented gas and kerosene space heaters, including CO, NO, NO[sub 2], formaldehyde, and respirable particles. The emission rates of these vary with heater technology such as burner design and operating conditions. Recent advances in infrared radiant gas burner technology have led to the development of a radiant fiber-matrix gas burner that exhibits lower emissions of some of these constituents. The development of a suitable configuration may result in a heater which can be used in residential and commercial gas appliances where reduced CO and NO[sub 2] are desired. This report presents laboratory measurements of pollutant emission rates from a prototype radiant fiber-matrix gas burner under several different operating conditions. Emission rates were quantified for CO, NO, NO[sub 2] and oxides of nitrogen (NO[sub x] = NO + NO[sub 2]) reported as nitrogen [N(of NO[sub x])]. 7 refs., 1 fig., 2 tabs.

Turbulent unvented gas explosions under dynamic mixture injection conditions

The paper addresses the question of the effect of turbulence on the development of gas explosions by discussing experimental results obtained in a 1.35-m3 spherical vessel. The turbulence is introduced by flow injection into the test volume from a high-pressure source. The evolution of the transient turbulence field is characterized through time-resolved velocity measurements made with a bi-directional probe specifically developed for the application. Data are presented for one (9.5%) methane-air and two (4.0 and 4.8%) propane-air mixtures for turbulence intensities up to 13 m/s, corresponding to an estimated turbulence Reynolds number of 41,900 based on the integral length scale. Values of equivalent turbulent burning velocity calculated from the initial rise of the pressure traces are similar for the three tested mixtures. Maximum rate of pressure rise data, on the other hand, show increasing reactivities of the mixtures in the order 9.5% CH4 to 4.0% and 4.8% C3H8. Furthermore, for each mixture, the maximum rate of pressure rise increases linearly with turbulence intensity. No evidence of quenching is apparent in the data, even though estimated values for the Karlovitz stretch factor indicate, that quenching conditions should have been approached at the high end of the range of turbulence tested.

Measurements of nitrous acid inside two research houses

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Indoor Nitrogen Dioxide Exposure and Children’s Pulmonary Function

Elevated concentrations of nitrogen dioxide (NO2) are produced in the home by the use of unvented gas appliances. In studies on potential health effects of indoor exposure to NO2, exposure has mostly been estimated from the presence or absence of sources like gas cookers in the home. This leads to misclassification of exposure, as NO2 concentrations in the home depend also on source use, ventilation habits, time budgets, etc. The availability of cheap, passive monitoring devices has made it possible to measure indoor concentrations of NO2 directly in health effects studies, albeit with averaging times of one to several days. So far, it has not been evaluated whether this increases the sensitivity of a study to detect health effects of NO2. In this paper, a comparison is made between NO2 sources and weekly average indoor NO2 measurements, as predictors of pulmonary function in a study among children aged 6-12 years. The relationship between exposure and lung functions was found to be generally non-significant in this study. The results further suggested that in this study, measuring indoor NO2 concentrations with passive monitors offered no advantage over the simple use of source presence as exposure variable.