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1.
In this study, 30 subjects were exposed to different combinations of air temperature (Ta: 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 Ta = 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 Ta 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 Ta 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 Ta and CO2 concentration on human responses was identified. 相似文献
2.
Physiological responses during exposure to carbon dioxide and bioeffluents at levels typically occurring indoors
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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. 相似文献
3.
Effects of exposure to carbon dioxide and bioeffluents on perceived air quality,self‐assessed acute health symptoms,and cognitive performance
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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. 相似文献
4.
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. 相似文献
5.
Douglas H. Taylor Kirk E. Lagory Daniel J. Zaccaro Ronald J. Pfohl R.Dana Laurie 《The Science of the total environment》1985
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. 相似文献
6.
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. 相似文献
7.
Edmondo Canelli 《Water research》1980,14(10):1533-1540
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. 相似文献
8.
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. NOx emission reduced appreciably owing to the catalytic activity of CeO2 nanoparticles. 相似文献
9.
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. 相似文献
10.
Liping Pang Jie Zhang Xiaodong Cao Xin Wang Jin Liang Liang Zhang Liang Guo 《Indoor air》2021,31(2):467-479
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. 相似文献
11.
Window/door opening‐mediated bedroom ventilation and its impact on sleep quality of healthy,young adults
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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. 相似文献
12.
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. 相似文献
13.
Health risk assessment on dietary exposure to polycyclic aromatic hydrocarbons (PAHs) in Taiyuan, China 总被引:5,自引:0,他引:5
Zhonghuan Xia Xiaoli Duan Di Liu Shu Tao Bin Lu Xinxin Hu 《The Science of the total environment》2010,408(22):5331-10242
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]Peq) 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. 相似文献
14.
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.]. 相似文献
15.
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. 相似文献
16.
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. 相似文献
17.
Chun-Ru Du Shun-Chih Wang Ming-Chih Yu Ting-Fang Chiu Jann-Yuan Wang Pei-Chun Chuang Ruwen Jou Pei-Chun Chan Chi-Tai Fang 《Indoor air》2020,30(3):422-432
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. 相似文献
18.
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 (Top) during non-heating seasons and more correlated to Top than CO2 levels during heating seasons. The impact of Top on ASVs decreases with an increase in CO2 levels, and the effect of CO2 levels on ASVs decreases with increase in Top. The most favorable ASVs are given when children feel “cool” and have “as it is” preference. By keeping CO2 < 1000 ppm and Top 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. 相似文献
19.
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. 相似文献
20.
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. 相似文献