Human responses to high levels of carbon dioxide and air temperature

In this study, 30 subjects were exposed to different combinations of air temperature (T_a: 24, 27, and 30°C) and CO₂ level (8000, 10 000, and 12 000 ppm) in a high-humidity (RH: 85%) underground climate chamber. Subjective assessments, physiological responses, and cognitive performance were investigated. The results showed that as compared with exposure to T_a = 24°C, exposure to 30°C at all CO₂ levels caused subjects to feel uncomfortably warm and experience stronger odor intensity, while increased mental effort and greater intensity of acute health symptoms were reported. However, no significant effects of T_a on task performance or physiological responses were found. This indicated that subjects had to exert more effort to maintain their performance in an uncomfortably warm environment. Increasing CO₂ from 8000 to 12 000 ppm at all T_a caused subjects to report higher rates of headache, fatigue, agitation, and feeling depressed, although the results were statistically significant only at 24 and 27°C. The text typing performance and systolic blood pressure (SBP) decreased significantly at this exposure, whereas diastolic blood pressure (DBP) and thermal discomfort increased significantly. These effects suggest higher arousal/stress. No significant interaction effect of T_a and CO₂ concentration on human responses was identified.     

Physiological responses during exposure to carbon dioxide and bioeffluents at levels typically occurring indoors

Twenty‐five subjects were exposed to different levels of carbon dioxide (CO₂) and bioeffluents. The ventilation rate was set high enough to create a reference condition of 500 ppm CO₂ with subjects present; additional CO₂ was then added to supply air to reach levels of 1000 or 3000 ppm, or the ventilation rate was reduced to allow metabolically generated CO₂ to reach the same two levels (bioeffluents increased as well). Heart rate, blood pressure, end‐tidal CO₂ (ETCO₂), oxygen saturation of blood (SPO₂), respiration rate, nasal peak flow, and forced expiration were monitored, and the levels of salivary α‐amylase and cortisol were analyzed. The subjects performed a number of mental tasks during exposures and assessed their levels of comfort and the intensity of their acute health symptoms. During exposure to CO₂ at 3000 ppm, when CO₂ was added or ventilation was restricted, ETCO₂ increased more and heart rate decreased less than the changes that occurred in the reference condition. Exposure to bioeffluents, when metabolically generated CO₂ was at 3000 ppm, significantly increased diastolic blood pressure and salivary α‐amylase level compared with pre‐exposure levels, and reduced the performance of a cue‐utilization test: These effects may suggest higher arousal/stress. A model is proposed describing how mental performance is affected by exposure to bioeffluents.     

Effects of exposure to carbon dioxide and bioeffluents on perceived air quality,self‐assessed acute health symptoms,and cognitive performance

The purpose of this study was to examine the effects on humans of exposure to carbon dioxide (CO₂) and bioeffluents. In three of the five exposures, the outdoor air supply rate was high enough to remove bioeffluents, resulting in a CO₂ level of 500 ppm. Chemically pure CO₂ was added to this reference condition to create exposure conditions with CO₂ at 1000 or 3000 ppm. In two further conditions, the outdoor air supply rate was restricted so that the bioeffluent CO₂ reached 1000 or 3000 ppm. The same 25 subjects were exposed for 255 min to each condition. Subjective ratings, physiological responses, and cognitive performance were measured. No statistically significant effects on perceived air quality, acute health symptoms, or cognitive performance were seen during exposures when CO₂ was added. Exposures to bioeffluents with CO₂ at 3000 ppm reduced perceived air quality; increased the intensity of reported headache, fatigue, sleepiness, and difficulty in thinking clearly; and reduced speed of addition, the response time in a redirection task, and the number of correct links made in the cue‐utilization test. This suggests that moderate concentrations of bioeffluents, but not pure CO₂, will result in deleterious effects on occupants during typical indoor exposures.     

The effects of warmth and CO2 concentration,with and without bioeffluents,on the emission of CO2 by occupants and physiological responses

The emission rate of carbon dioxide (CO₂) depends on many factors but mainly on the activity level (metabolic rate) of occupants. In this study, we examined two other factors that may influence the CO₂ emission rate, namely the background CO₂ concentration and the indoor temperature. Six male volunteers sat one by one in a 1.7 m³ chamber for 2.5 h and performed light office-type work under five different conditions with two temperature levels (23 vs. 28°C) and three background concentrations of CO₂ (800 vs. 1400 vs. 3000 ppm). Background CO₂ levels were increased either by dosing CO₂ from a cylinder or by reducing the outdoor air supply rate. Physiological responses to warmth, added CO₂, and bioeffluents were monitored. The rate of CO₂ emission was estimated using a mass-balance equation. The results indicate a higher CO₂ emission rate at the higher temperature, at which the subjects were warm, and a lower emission rate in all conditions in which the background CO₂ concentration increased. Physiological measurements partially explained the present results but more measurements are needed.     

Effect of trichloroethylene on the exploratory and locomotor activity of rats exposed during development

Trichloroethylene (TCE) is a common contaminant of underground water supplies. To examine the effect of TCE on the developing central nervous system, rats were exposed to TCE throughout gestation until 21 days postpartum via their dams' drinking water. TCE concentrations of 312 mg/l, 625 mg/l and 1250 mg/l were tested. Exploratory behavior was higher in 60- and 90-day old male rats which were exposed to any level of TCE. The effect of TCE-exposure on locomotor activity (running wheel) was also examined in 60-day old males (625 and 1250 ppm exposure groups). Locomotor activity was significantly higher in rats exposed to 1250 ppm TCE. These data suggest that TCE has long-term effects on behaviour.     

Comparative effectiveness of antifouling treatment regimes using chlorine or a slow-releasing bromine biocide

Five chlorine (Cl₂) and three slow-releasing bromine biocide [1-bromo-3-chloro-5,5-dimethylhydantoin (BCDMH)] treatment regimes were compared under laboratory conditions to determine their effectiveness in controlling the fouling of 304L stainless steel heat exchanger tubing. The most effective Cl₂ treatments were low level (0.1 ppm or less) continuous applications. Three intermittent Cl₂ treatments (1 h day⁻¹ at 1.0 ppm, 1 h day⁻¹ at 0.5 ppm, and 3 × 20 min day⁻¹ at 0.5 ppm) were about equally effective. However, all three intermittent regimes were significantly less effective than the low level continuous treatments. The effectiveness of BCDMH treatment was similar to Cl₂ when used intermittently at similar residual concentrations as Cl₂ for 1 h day⁻¹ and continuously at low levels. These experiments indicated that low level continuous treatment was more effective than intermittent treatment for controlling biofouling.     

Evaluation of a portable bare-electrode amperometric analyzer for determining free chlorine in potable and swimming-pool waters

Chlorine in the forms of HOCl or ClO⁻ was determined rapidly and precisely in the range from 0.10 to 3.0 ppm chlorine, without titration, using a bare-electrode portable amperometric analyzer. The instrument was calibrated with a 1.00 ppm chlorine standard solution or an equivalent permanganate solution which is stable for at least 6 months. The detection limit was 0.10 ppm chlorine, and relative standard deviations (N = 10) were <6.0% in potable or swimming-pool waters containing 0.25, 1.00 and 2.50 ppm or 0.35, 1.40 and 2.70 ppm chlorine respectively. Bromine-, triiodide ion-, and Mn (VII)-generated signals were stoichiometrically equivalent to that of hypochlorite, but MnO₂ suspensions (1.5, 5.0 or 15 ppm) did not produce detectable amperometric signals.Analysis of solutions of hypochlorite with ammonium chloride or selected organic nitrogen compounds indicated that various N-chloro compounds may interfere. In the presence of N-chloroglycine (2.70 ppm chlorine) the amperometric signal was about 5% of that for the equivalent concentration of hypochlorite, but higher relative responses were obtained with NH₂Cl, NHCl₂ or NCl₃ (19, 42 and 70% at 2.60, 1.20 or 1.00 ppm chlorine respectively). Chlorinated urea (2.2 ppm N, 2.90 ppm chlorine), chlorinated bovine albumin (10 ppm albumin, 2.00 ppm chlorine) or monochloroisocyanurate (1.30 ppm chlorine) produced amperometric signals (76, <5 and 50% respectively) which are lower than those obtained by the N,N-diethyl-p-phenylenediamine (DPD) method (100, 12 and 92%).Twenty potable water samples were analyzed for free chlorine by the DPD and amperometric procedures. Statistical analysis showed no significant differences between the two sets of results (P < 0.1). Swimming-pool-water samples were also analyzed by the two methods in the field (22 samples) and in the laboratory (24 samples). In each set of results the mean free-chlorine value by the DPD procedure was significantly higher than that obtained amperometrically (P > 0.005). This discrepancy was associated with the probable presence of chlorinated urea, whose signal by amperometry is lower than that by the DPD method.The advantages of this simple procedure must be weighed against possible inaccurate results in the presence of NH₂Cl, NHCl₂ or NCl₃.     

Study of emission characteristics of a diesel engine using cerium oxide nanoparticle blended pongamia methyl ester

In this work cerium oxide (CeO₂) nanoparticle was added to pongamia methyl ester (PME) to study its impact on emission characteristics in a diesel engine. It was found that CeO₂ nanoparticles act as an oxygen shelter owing to its high surface energy content due to its huge surface to volume ratio which expedites the process of combustion. Cerium oxide nanoparticles were mixed with neat PME at a different dose of 50?ppm and 100?ppm on a mass basis. CeO₂ nanoparticles are mixed to biodiesel by means of ultrasonicator and magnetic agitator to make sure homogenous. A diesel engine was used for the experimental analysis and fuelled with neat PME, diesel, PME dozed with CeO₂ nanoparticles at 50?ppm (PMEA50) and 100?ppm (PMEA100). Experimental results revealed that nanoparticle had an affirmative effect on emissions of PME as CeO₂ nanoparticles acted as a catalyst of oxidation. Amid the fuels containing CeO₂ nanoparticles, PMEA100 showed an improvement in various emissions as compared to conventional fuels. CeO₂ nanoparticles were to be the superior oxidising catalyst as it could effectively reduce CO and HC emissions. NO_x emission reduced appreciably owing to the catalytic activity of CeO₂ nanoparticles.     

Comparative effectiveness of chlorine and chlorine dioxide biocide regimes for biofouling control

The effectiveness of chlorine (Cl₂) and chlorine dioxide (ClO₂) in controlling biofouling of 304L stainless steel heat exchanger tubing was compared using an experimental trough system. Three combinations of dose and contact time were evaluated. Chlorination coupled with a dispersant was also tested. Three criteria were used to assess the degree of fouling; organic carbon and dry weight of the fouling material accumulated on metal specimens and the visual appearance of this material on the specimens. These parameters correlated well with one another and therefore, collectively provided an effective means of evaluating biocide efficacy.Metal specimens in all troughs receiving biocide treatment were much less fouled than those in the trough receiving no biocide. Continuous application of Cl₂ at about 0.15 ppm was more effective than four 15-min 1 ppm Cl₂ applications per day. Both of these treatment regimes were more effective than a dose of about 1 ppm for 1 h day⁻¹. Use of a dispersant in combination with Cl₂ showed no significant reduction in the amount of biofouling material accumulation, although a difference in the texture of this material was observed. Unlike the Cl₂ results, low-level continuous ClO₂ treatment at 0.15 ppm resulted in biofouling similar to that when 1 ppm of ClO₂ was used for 1 h day⁻¹. Overall, ClO₂ was significantly (P < 0.05) more effective in controlling biofouling than Cl₂.     

The effects of carbon dioxide exposure concentrations on human vigilance and sentiment in an enclosed workplace environment

In this study, fifteen participants were exposed to different carbon dioxide (CO₂) concentrations in an enclosed environmental chamber to investigate the potential effects of elevated CO₂ concentrations on human vigilance and sentiment. The psychomotor vigilance test (PVT), the Karolinska Sleepiness Scale (KSS), and the Positive and Negative Affect Schedule (PANAS) were measured before and after each 4-hour CO₂ exposure session. The statistical analyses of the PVT performance metrics showed that the human vigilance decreased significantly with the elevated CO₂ concentration from 1500 ppm to above 3500 ppm, but no significant change was observed in the KSS score. Moreover, although the participants reported less positive and more negative emotions as the CO₂ exposure concentration increased, the effect of CO₂ concentration on human sentiment was not potent. In sum, the findings suggested a detrimental effect of CO₂ exposure concentration on human vigilance at the CO₂ concentration of 3500 ppm, which is below the current occupational exposure limit of 5000 ppm. It is worth noting that the order of CO₂ exposures was not balanced among the participants, which remains a major limitation of this study.     

Window/door opening‐mediated bedroom ventilation and its impact on sleep quality of healthy,young adults

This work examined window/door opening as means of bedroom ventilation and the consequent effect upon occupants’ sleep, using data from 17 healthy volunteers. Bedroom CO₂ level, temperature, and relative humidity were measured over 5 days, for two cases: open window or door (internal, bedroom door), and closed window and door. Participant filled questionnaires and sleep diary provided subjective measure of sleep quality. Actigraphy objectively monitored the participants during sleep. Additionally, a FlexSensor, placed under pillows of participants, detected movement during sleep. Average CO₂ level for the Open conditions was 717 ppm (SD = 197 ppm) and for Closed conditions was 1150 ppm (SD = 463 ppm). Absolute humidity levels were similar for both conditions, while Open conditions were slightly cooler (mean = 19.7°C, SD = 1.8°C) than Closed (mean = 20.1°C, SD = 1.5°C). Results showed significant correlations (P < .001) between actigraphy data and questionnaire responses for: sleep latency (r = .45), sleep length (r = .87), and number of awakenings (r = .28). Of all analyzed sleep parameters, questionnaire‐based depth of sleep (P = .002) and actigraphy‐based sleep phase (P = .003) were significantly different between Open and Closed conditions.     

Cardiovascular and respiratory changes in rainbow trout, Salmo gairdneri, exposed intermittently to chlorine

Heart rate, ventilation frequency, coughing rate, arterial blood Po₂, pH, lactate, methemoglobin, and hematocrit were monitored serially in trout exposed to free chlorine thrice daily of 0.4 or 0.5 mg l⁻¹ peak residual concentration. A simultaneous bradycardia and hyperventilation occurred with each pulse of chlorine. Coughing rate rose 15-fold during each chlorination. All three parameters tended to return toward normal rates between pulses with recovery being noticeably better in 0.4 ppm chlorine pulses.Arterial Po₂ dropped to 40% of the control value during the peak of the first pulse and pH declined 0.25 units. Subsequent chlorine pulses caused more severe declines and progressively less interpulse recovery of these parameters. Blood lactate and hematocrit values were significantly elevated. Methemoglobin rose in concentration but not to a physiologically significant level. It is concluded that free chlorine kills fish by internal hypoxia induced by damage to the gills.     

Health risk assessment on dietary exposure to polycyclic aromatic hydrocarbons (PAHs) in Taiyuan, China

Twenty-five kinds of seven categories of foods were sampled in December 2008 and the concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) were determined. The highest level of total PAHs was detected in pork (195.30 ng/g) whereas the lowest concentration was found in milk (8.73 ng/g). The median values of B[a]P equivalent (B[a]P_eq) daily exposure doses for children, adolescents, adults and seniors of male were estimated to be 392.42, 511.01, 571.56 and 532.56 ng/d, respectively, whereas those for the above population groups of female were found to be 355.16, 440.51, 487.64 and 444.85 ng/d, respectively. The incremental lifetime cancer risk (ILCR) values at the 22.1th, 26.1th, 12.7th, 24.9th, 22.7th, 27.0th, 12.9th, and 25.5th percentiles for male children, male adolescents, male adults, male seniors, female children, female adolescents, female adults and female seniors, respectively, were larger than 10^− 6, indicating high potential carcinogenic risk, and were larger than 10^− 4 at the 74.5th, 78.7th, 60.6th, 77.4th, 75.3th, 79.5th, 60.8th and 77.9th percentiles for the above groups, respectively, which implied significant cancer risk. Sensitivity analysis found that the two variables of oral cancer slope factor of benzo(a) pyrene (SF) and the daily dietary PAH exposure level (ED) had the greater impact than that of body weight (BW) on the ILCR.     

Hydrogen sulfide (H2S) and sour gas effects on the eye. A historical perspective

The toxicology of hydrogen sulfide (H₂S) and sour gas on the eye has a long history beginning at least with Ramazzini's observations [Ramazzini B. Diseases of Workers—De Morbis Artificum Diatriba—1713. Wright WC (trans). New York, C. Hafner Publishing Co Inc.; 1964. 98-99 pp.]. In contrast, a recent review by Alberta Health and Wellness (AHW Report) concluded that there is little evidence of eye irritation following short-term exposures to H₂S at concentrations up to 100 ppm and that the H₂S literature on the eye is a series of unsubstantiated claims reproduced in review articles dating back to the 1930s [Alberta Health and Wellness (AHW report). Health effects associated with short-term exposure to low levels of hydrogen sulfide: a technical review, Alberta Health and Wellness, October 2002, 81pp.]. In this paper, we evaluated this claim through a historical review of the toxicology of the eye. Ramazzini noted the effects of sewer gas on the eye [Ramazzini B. Diseases of Workers—De Morbis Artificum Diatriba—1713. Wright WC (trans). New York, C. Hafner Publishing Co Inc. 1964. 98-99 pp.]. Lehmann experimentally showed eye effects in men at 70-90 ppm H₂S and also in animals [Lehmann K. Experimentalle Studien uber den Einfluss technisch und hygienisch wichtiger Gase und Dampfe auf den Organismus. Arch Hyg 1892;14:135-189]. In 1923, Sayers, Mitchell and Yant reported eye effects in animals and men at 50 ppm H₂S. Barthelemy showed eye effects in animals and men at 20 ppm H₂S [Barthelemy HL. Ten years' experience with industrial hygiene in connection with the manufacture of viscose rayon. J Ind Hyg Toxicol 1939;21:141-51]. Masure experimentally showed that H₂S is the causative agent of eye impacts in animals and men [Masure R. La Keratoconjunctivite des filatures de viscose; etude clinique and experiementale. Rev Belge Pathol 1950;20:297-341]. Michal upon microscopic examination of the rat's cornea, found nuclear pyknosis, edema and separation of cells in the eye following exposures for 3 h at 36 ppm H₂S [Michal FV. Eye lesions caused by hydrogen sulfide. Cesk Ophthalmol 1950;6;5-8]. In 1975, in Alberta, irreversible eye damage and photophobia were experimentally produced in calves exposed to 20 ppm H₂S for 1 week [Nordstrom GA. A study of calf response of ammonia and hydrogen sulfide gases. Thesis, University of Alberta, Department of Agricultural Engineering, Edmonton Alberta; 1975, 218 pp.]. Alberta Environmental Centre documented clinical irritation of the eye at 40 ppm H₂S in 6 hours in rats [Alberta Environmental Centre. Morphological observations in rats exposed for six hours to an atmosphere of 0, 56, or 420 mg/m³ hydrogen sulfide. AECV86-A1. Alberta Environmental Centre, Vegreville, Alberta; 1986b. 28 pp.]. In two sour gas blow-outs in Alberta, in the early 1980s, eye injury was documented in humans and animals at 0.5 ppm H₂S. Community studies in the United States, Europe and New Zealand suggest that acute exposure to 25 ppb H₂S is the lowest concentration to irritate the eyes; with chronic exposure, serious eye effects are suggested. In contrast to the conclusion, all of the studies, except one, cited in the AHW Report indicate toxic effects on the eye below 100 ppm H₂S [Alberta Health and Wellness (AHW report). Health effects associated with short-term exposure to low levels of hydrogen sulfide (H₂S): a technical review, Alberta Health and Wellness, October 2002, 81pp.]. In addition, the AHW Report (2002) mis-presented two studies as ‘clinical studies’, claiming they reported no evidence of eye effects in humans from 2 and 30 ppm H₂S for 30-40 minutes [Alberta Health and Wellness (AHW report). Health effects associated with short-term exposure to low levels of hydrogen sulfide (H₂S): a technical review, Alberta Health and Wellness, October 2002, 81pp.].     

The effects of bedroom air quality on sleep and next‐day performance

The effects of bedroom air quality on sleep and next‐day performance were examined in two field‐intervention experiments in single‐occupancy student dormitory rooms. The occupants, half of them women, could adjust an electric heater to maintain thermal comfort but they experienced two bedroom ventilation conditions, each maintained for 1 week, in balanced order. In the initial pilot experiment (N = 14), bedroom ventilation was changed by opening a window (the resulting average CO₂ level was 2585 or 660 ppm). In the second experiment (N = 16), an inaudible fan in the air intake vent was either disabled or operated whenever CO₂ levels exceeded 900 ppm (the resulting average CO₂ level was 2395 or 835 ppm). Bedroom air temperatures varied over a wide range but did not differ between ventilation conditions. Sleep was assessed from movement data recorded on wristwatch‐type actigraphs and subjects reported their perceptions and their well‐being each morning using online questionnaires. Two tests of next‐day mental performance were applied. Objectively measured sleep quality and the perceived freshness of bedroom air improved significantly when the CO₂ level was lower, as did next‐day reported sleepiness and ability to concentrate and the subjects' performance of a test of logical thinking.     

Effects of mercury accumulation on the electrophoretic patterns of the serum, haemoglobin and eye lens proteins of Tilapia mossambica (Peters)

Two test concentrations of mercury (0.01 and 0.04 ppm) were used for studies on the uptake of mercury by the tissues and alteration in the electrophoretic patterns of blood serum, haemoglobin and eye lens proteins. Haemoglobin showed an increase in protein in the faster moving band. Significant changes were seen in the patterns of serum protein with respect to number, mobility and intensity of the protein fractions in the fish exposed to higher concentration of mercury (0.04 ppm). The patterns of eye lens protein were quite constant throughout the period of exposure.Short-term experiments on the fish serum electrophoresis were carried out using higher concentrations of mercury in the medium (0.4, 0.6 and 0.8 ppm). These were just below the lethal level. Sampling was done at 3, 24, 48 and 72 h intervals. From 24 h onwards there was a significant increase in the intensity of the lower mobility bands and there was a decrease in the higher mobility bands. After 48 and 72 h, a distinct extra band was seen between the first two fast-moving bands at all the three high concentrations of mercury used. These patterns were very similar to the pattern observed with the lower concentration of mercury in the medium (0.04 ppm) after the 11th week exposure period, which was found to affect the survival or growth potential of the fish. This study shows that exposure to a large amount of mercury over a short period has an effect similar to small amounts over a long period. The serum electrophoretic patterns obtained after 48 and 72 h exposures to sublethal concentrations of mercury, and which were similar to the one obtained in 0.04 ppm mercury concentration after the 11th week exposure period, can be regarded as the “stress pattern” of T. mossambica serum. The use of fish blood morphology as a biological index of water quality has been indicated.     

Effect of ventilation improvement during a tuberculosis outbreak in underventilated university buildings

The role of ventilation in preventing tuberculosis (TB) transmission has been widely proposed in infection control guidance. However, conclusive evidence is lacking. Modeling suggested the threshold of ventilation rate to reduce effective reproductive ratio (ratio between new secondary infectious cases and source cases) of TB to below 1 is corresponding to a carbon dioxide (CO₂) level of 1000 parts per million (ppm). Here, we measured the effect of improving ventilation rate on a TB outbreak involving 27 TB cases and 1665 contacts in underventilated university buildings. Ventilation engineering decreased the maximum CO₂ levels from 3204 ± 50 ppm to 591-603 ppm. Thereafter, the secondary attack rate of new contacts in university dropped to zero (mean follow-up duration: 5.9 years). Exposure to source TB cases under CO₂ >1000 ppm indoor environment was a significant risk factor for contacts to become new infectious TB cases (P < .001). After adjusting for effects of contact investigation and latent TB infection treatment, improving ventilation rate to levels with CO₂ <1000 ppm was independently associated with a 97% decrease (95% CI: 50%-99.9%) in the incidence of TB among contacts. These results show that maintaining adequate indoor ventilation could be a highly effective strategy for controlling TB outbreaks.     

Perceived indoor air quality in naturally ventilated primary schools in the UK: Impact of environmental variables and thermal sensation

Indoor air quality (IAQ) in classrooms has a significant impact on children's academic performance, health, and well-being; therefore, understanding children's perception of IAQ is vital. This study investigates how children's perception of IAQ is affected by environmental variables and thermal sensation. In total, 29 naturally ventilated classrooms in eight UK primary schools were selected and 805 children were surveyed during non-heating and heating seasons. Results show that air sensation votes (ASVs) are more correlated to CO₂ levels than to operative temperatures (T_op) during non-heating seasons and more correlated to T_op than CO₂ levels during heating seasons. The impact of T_op on ASVs decreases with an increase in CO₂ levels, and the effect of CO₂ levels on ASVs decreases with increase in T_op. The most favorable ASVs are given when children feel “cool” and have “as it is” preference. By keeping CO₂ < 1000 ppm and T_op within children's thermal comfort band, ASVs are improved by 43%. The study recommends that standards should consider the impact of both temperature and CO₂ levels on perceived IAQ. Perception of IAQ also affects children's overall comfort and tiredness levels; however, this influence is more significant on tiredness level than that on overall comfort level.     

Preserving Shipboard AFFF Fire Protection System Performance While Preventing Hydrogen Sulfide Formation

There is a very serious problem aboard US Navy ships from generation of toxic hydrogen sulfide (H₂S) in Aqueous Film-Forming Foam (AFFF) solutions used for shipboard fire protection. This is the result of the action of sulfate reducing bacteria (SRB) in mixtures of seawater and AFFF, which remain stagnant for significant time periods in shipboard fire protection system piping. Similar to microbial generation of H₂S in sewage, over time microbes present in seawater consume organic materials in the AFFF mixture and can deplete the dissolved oxygen. If the reduction-oxidation potential falls low enough, anaerobic action of the SRB on the sulfate present in seawater can then result in H₂S generation, reaching dangerous levels. The recommended ceiling for exposure to H₂S is only 10 ppm. If the microbes causing oxygen depletion and/or the SRB can be eliminated (or sufficiently minimized), the dangerous generation of H₂S would not occur. The Navy Technology Center for Safety and Survivability is participating in a research project for the Naval Sea Systems Command (NAVSEA) to evaluate several treatment modalities for their ability to inhibit H₂S formation in AFFF/seawater mixtures and for possible deleterious effects on AFFF performance. Various approaches have been considered employing laboratory evaluations (dynamic surface tension and Ross-Miles foamability), and 28 ft² (2.6 m²) pool fire extinguishment and burnback protection field tests (Military Standard MIL-F-24385F). The protocol selected for NAVSEA shipboard H₂S generation mitigation testing is a combination of a commercial broad-spectrum biocide with a molybdenum compound which is a specific inhibitor of SRB.     

Surface neutralization and H₂S oxidation at early stages of sewer corrosion: influence of temperature, relative humidity and H₂S concentration

While the involvement of a range of environmental factors in sewer corrosion is known, a comprehensive understanding of the processes involved and the exact role of individual environmental factors in sewer corrosion is still lacking. The corrosion of concrete in sewer systems is reported to be initiated through chemical reactions (involving H₂S and CO₂) that lower the surface pH to a level then conducive for biological activity. However, the specific influence of environmental variables, such as H₂S level, temperature, and relative humidity etc. remains unclear; although, they are expected to control these initial surface reactions of the concrete sewer pipe. We examined changes in the surface chemistry of concrete during the early stages of corrosion by exposing concrete coupons to thirty-six independent conditions in well-controlled laboratory chambers that simulated conditions typically found in various sewer environments across Australia. The conditions employed were combinations of six H₂S levels, three gas-phase temperatures and two relative humidity levels. Our results indicate that the role of CO₂ on initial surface pH reduction is insignificant when compared to the influence of H₂S. Within the first 12 months, a decrease in surface pH by 4.8 units was observed for coupons exposed to 30 °C and 50 ppm H₂S, while significantly lower pH reductions of 3.5 and 1.8 units were detected for coupons exposed to 25 °C and 18 °C respectively, and 50 ppm H₂S. Elemental sulphur was found to be the major oxidation product of H₂S and elevated concentrations were detected at the higher levels of H₂S, temperature and relative humidity. More significantly, the data obtained from the controlled chamber experiments correlated with those obtained from the field-exposed coupons. Hence, these findings can be extended to real sewer corrosion processes.