Design of Workplace Dilution and Local Ventilation Systems

Chapter 6 - Commissioning, control, and maintenance of ventilation systems

In response to a request from the President of Simmons Industries, Inc. (SIC-2015), Siloam Springs, Arkansas, the ability of the local exhaust ventilation system in the hanging room of the poultry processing facility to protect chicken hangers from exposures to airborne organic dust was evaluated. Air quality analyses were conducted both at the Siloam Springs facility and at the similar facility of the same company located in Jay, Oklahoma. One of three 8 hour time weighted average (TWA) inhalable dust concentrations from the Siloam Springs facility exceeded the Threshold Limit Value of 10mg/cu m for particulates not otherwise classified. Three similar samples taken at the Jay facility exceeded the limit. The Jay facility did not have a local ventilation system in operation. Endotoxin concentrations in all six of the TWA inhalable samples exceeded the recommended limit of 10 nonagrams/cubic meter (ng/cu m) at both facilities. Of the six samples, five exceeded 100ng/cu m, a level associated with spirometric evidence of acute airways obstruction. The authors conclude that exposures in the hanging rooms of both poultry processing facilities represented a potential health risk. The authors recommend that the exhaust ventilation system and work practices be changed to reduce exposures. A respiratorymore » protection program should be implemented until dust exposures are controlled.« less

The allocation of intake air stream in pig premises is not evenly. The existence of engineer-ing networks and equipment, the breaching of montage technologies of air ventilation, incorrect maintenance of air ventilation system – all these factors bring to many breaches and problems. This problem such as air exchange violation in all premises, appearing zones of stasis (aero stasis), and others. As a result of which the differential of temperature and humidity has appeared. These also appear excess maximum per-mitted concentration of dust and gases. The all-exchanged ven-tilation system can’t solve all problems in local zones in pig premises. In this local air-ventilation system become more demand. For effective work of local air ventilation, the question of deter-mining installation sites for the air purification of pig premises local system elements should be solved. Keywords: LOCAL VENTILATION, AIR CLEANING FROM DUST, DUST RELEASE, HARMFUL GAS CLEANING

Acute and chronic exposure to xylene can result in a range of negative health effects. However, xylene is widely used and emitted in the air of workplaces. To evaluate xylene vapor concentrations to guide the design and evaluation of a local exhaust ventilation (LEV) system to reduce exposure in a pesticide production factory. A real time volatile organic compound (VOC) monitor was used to determine the workers' time-weighted average (TWA) exposure. A LEV system was designed, and then, workers' exposure to xylene vapor was evaluated. We found that worker's exposure to xylene (4·7±5·5 ppm) was lower than the standards recommended by the American Conference of Governmental Industrial Hygienists (ACGIH) and the Occupational safety and health administration (OSHA). Despite the low TWA exposures, the short-term exposures for some workers were higher than STEL levels. Three canopy hoods were designed and installed with capture velocities of 0·508 m second(-1) and duct velocity of 10·16 m second(-1). We found that an exhaust ventilation system had a significantly reduced occupational exposure to xylene vapor.

The design of tunnel ventilation system for a long vehicular tunnel

Research of the microclimate formed by the local DCV

The vortex ventilator (VV) is a new concept of a local exhaust ventilation system that uses a vortex flow to improve the directional capture ability and thus overcomes the critical defects of the general local exhaust ventilation (LEV) system. The LEV has a rapid decrease of the capture velocity with distance from the exhaust inlet, resulting in a very poor capture efficiency when contaminants are generated far away from the exhaust inlet. In this study, the capture characteristics of the VV are evaluated with respect to the capture efficiency as well as the capture velocity. Three-dimensional computational fluid dynamics simulations are performed together with experiments using the tracer gas method with SF6. Compared with simple suction, the VV gives more than nine times as large a capture velocity and thus has a capture efficiency of higher than 70%. The larger capture velocity and the higher capture efficiency of the VV guarantee a more flexible layout of the equipment in the working area.

Experimental study of a local ventilation strategy to protect semi-exposed relics in a site museum

Industrial cleaning processes are a major source of emissions of chlorinated organic solvents in Japan. Solvent emission mechanisms from metal cleaning processes were analysed to support process improvement aimed at emission reductions. The amounts of solvents directly emitted from a washing machine and solvents taken out by metal parts to be cleaned were measured in laboratory experiments using an industrial washing machine. Direct emissions to a local ventilation system and to the workplace were analysed, while several process conditions were changed. The drying rate of solvents on surfaces was analysed for seven metal parts to clarify the effects of their materials and shape. The results for direct solvent emissions show that solvents emitted because of the movement of metal parts inside a washing machine can be mainly exhausted through a local ventilation system, while the operation of an ultrasonic device can increase solvent diffusion to the workplace. Lowering the cooling water temperature can be effective in avoiding such solvent diffusion to the workplace. The results also show that the heat capacity and shape complexity of metal parts can affect the drying rate of solvents on their surfaces. Analysis of the results shows the effectiveness of using a local ventilation system and cooling pipes in controlling solvent emissions for several work tasks. The minimum time required to dry all solvents on the surface of metal parts was also estimated. Analyses of the emission mechanisms in this study clarified the major factors in solvent emissions and the effectiveness of process modifications for emission reductions. The findings are applicable to practical process improvement aimed at emission reductions in cleaning sites.

The research objectives were:- 1.To review the literature to establish the factors which have traditionally been regarded as most crucial to the design of effectlve exhaust ventilation systems. 2. To design, construct, install and calibrate a wind tunnel. 3. To develop procedures for air velocity measurement followed by a comprehensive programme of aerodvnamic data collection and data analysis for a variety of conditions. The major research findings were:- a) The literature in the subject is inadequate. There is a particular need for a much greater understanding of the aerodynamics of the suction flow field. b) The discrepancies between the experimentally observed centre-line velocities and those predicted by conventional formulae are unacceptably large. c) There was little agreement between theoretically calculated and observed velocities in the suction zone of captor hoods. d) Improved empirical formulae for the prediction of centre-line velocity applicable to the classical geometrically shaped suction openings and the flanged condition could be (and were) derived. Further analysis of data revealed that: - i) Point velocity is directly proportional to the suction. flow rate and the ratio of the point velocity to the average face velocity is constant. ii) Both shape, and size of the suction opening are significant factors as the coordinates of their points govern the extent of the effect of the suction flow field. iii) The hypothetical ellipsoidal potential function and hyperbolic streamlines were found experimentally to be correct. iv) The effect of guide plates depends on the size, shape and the angle of fitting. The effect was to very approximately double the suction velocity but the exact effect is difficult to predict. v) The axially symmetric openings produce practically symmetric flow fields. Similarity of connection pieces between the suction opening and the main duct in each case is essential in order to induce a similar suction flow field. Additionally a pilot study was made in which an artificial extraneous air flow was created, measured and its interaction with the suction flow field measured and represented graphically.

ВПЛИВ ОБРОБІТКУ ҐРУНТУ

This paper presents the results of a series of recent studies to investigate the improved optimal design and planning of the main ventilation systems of complex multi-level mine networks using a genetic algorithm (GA) routine. It is concluded that the method may be successfully used to investigate the benefits offered by alternative ventilation configurations and to determine the most practical and cost-effective ventilation system during the various mine planning stages (short-, medium- and long-term). In particular, the optimum number, location and duties of booster fans, and size and location of regulators may be evaluated and selected. The objective of the final ventilation design is to identify the ventilation system that operates in both a safe and energy-efficient manner. The method has been refined to include the selection of practical fan units that match the optimal fan operating duties determined by the GA routine. The paper also reviews general optimisation strategies that may be employed to enhance and maintain the performance of mine ventilation systems.

Ventilation is used to control indoor air quality for maintaining the health and performance of human and ensuring healthy environment. It is known that the environmental criteria are dictated by temperature, humidity, and contamination. In a case study at XY company, questionnaires were distributed to the workers and interviews were conducted to find out the level of satisfaction on working conditions in certain areas. 70% respondents reported feeling uncomfortable because of heat, dust and hot environment. An analysis of indoor air quality was carried out to measure the temperature at pouring area. Based on the analysis, the range of temperatures is from 35°C to 43°C. A local exhaust ventilation (LEV) system was design for improve indoor air quality and reduce extreme heat. The LEV system was proposed for the pouring area to capture then discharged heat or contaminants through a series of strategically placed overhead ducts.

A new technique to measure the performance of local exhaust ventilation systems has been developed and tested in both the laboratory and the field. The technique involves the measurement of the capture efficiency of exterior hoods, defined to be the fraction of contaminants given off by a process captured by the exhaust system serving that process. Capture efficiency measurement can be a powerful tool in the evaluation of local exhaust systems, since it is a direct, quantitative measure of system performance; in contrast, indices of performance now in use are either qualitative or measure quantities which may not be related directly to system performance. A basic theory for capture efficiency has been developed, and a prototype system for measuring capture efficiency has been constructed and tested. Preliminary laboratory and field measurements using the system have demonstrated the power of the method, which should find widespread use in the design of new ventilation systems and the evaluation of existing ones.

To the Editor: Li et al1 evaluated workplace exposures to 1-bromopropane (CASRN 106-94-5) at three separate manufacturing facilities in China (ie, Yixing, Yancheng, and Weifang).1 The authors identified a number of statistically significant changes in various endpoints evaluated in female and male workers. Li et al1 reported that women were more susceptible than men and identified a lowest adverse effect level (LAEL) of 1.28 ppm in women on the basis of vibration sense in toes (as graded by different observers) and red blood cell (RBC) count. Herein, we discuss several issues regarding these workplaces and associated cohorts, the endpoints evaluated, and the conclusions drawn by Li et al.1 First, several manufacturers of 1-bromopropane have performed a number of mammalian toxicology studies under good laboratory practice standards and according to validated testing guidelines. The route of exposure in these good laboratory practice studies was primarily but not exclusively via inhalation. Toxicity studies included acute, prenatal developmental, 28-day repeated concentration, 90-day repeated concentration, and two-generation reproduction. The US National Toxicology Program's Center for the Evaluation of Risks to Human Reproduction summarized and critically evaluated the aforementioned studies, along with studies performed in academic laboratories.2 On the basis of the results of the foregoing studies, safety data sheets were developed and are provided to customers. For example, Albemarle Corporation's Asia Pacific safety data sheet for 1-bromopropane states the following under the “Hazard Statements” and “Exposure controls/personal protection”:3 “Hazard Statements May damage fertility or the unborn child May cause drowsiness and dizziness Harmful: danger of serious damage to health by prolonged exposure through inhalation” “Exposure controls/personal protection Ventilation controls Use with local exhaust ventilation. Use only in well ventilated areas. Hygiene measures Avoid contact with skin, eyes and clothing. Wash thoroughly after handling. Personal protective equipment Wear suitable protective clothing, gloves and eye/face protection. Respiratory protective equipment Full facepiece approved respirator fitted with an organic vapour canister. The Albemarle Workplace Exposure Guideline of the major substance of the preparation is 25 ppm TWA8.” These measures are communicated to customers in the native language of the region to ensure the safe handling and use of this substance. In contrast, Li et al1 stated: “[n]one of the workers wore masks or gloves during the operation.” The authors also noted that “[t]he factory windows and doors were wide open during working hours, and a few exhaust fans were installed in each factory.” For one of the factories (ie, Yixing), Li et al1 cited to their previous description of this workplace, where they observed: “[i]n each plant, a ventilating fan was ineffectively installed 6 m from the floor; no local ventilation fan was installed in the vicinity of the areas where workers might be exposed to [1-bromopropane].”4 Li et al1 observed the following exposure opportunities in each of the three factories: “” adding of the chemicals into the reaction pots; sitting close to the reaction pots to observe and record the temperature; taking out the crude product; adding hydrogen carbonate and stirring; or pouring the product into the 1000-L drums. “In the final step, the workers added the product with hand scoops to adjust the product volume in the drum.” The situation noted earlier is troubling because the known hazards of 1-bromopropane have been properly communicated in the public domain, along with the necessary mechanical measures and personal protective equipment to ensure safe use. On the basis of the unacceptable practices reported by Li et al,1 the workers may have received significant exposures via the inhalation and dermal routes (eg, splashing). Though not reported by the authors, oral exposures might have also occurred if the workers were drinking and eating at their workstations, or contacting their hands with their mouths. Therefore, because airborne exposure levels were used as a surrogate for internal dose, this study may have suffered from underestimation of actual exposures by not considering dermal and oral exposures to the participants. Second, Li et al1 used various sex-, age-, and region-matched controls against the three cohorts, including workers from a beer factory (2001, Yixing), a refrigeration equipment factory (2003, Yixing), a knitting workshop (2004, Yixing), and a steel operation factory (2005, Weifang). No exposure monitoring data were provided on the unique types of exposures that the worker controls may have encountered in their specific industries or locales (eg, blood lead or methyl mercury levels). Chemical exposure information was limited to worker recall. Third, the following biochemistry, endocrinology, and hematology endpoints were reported as being statistically significantly different in exposed female workers and the controls: lactate dehydrogenase, thyroid stimulating hormone, follicle stimulating hormone, estradiol, white blood cell count, RBC count, hemoglobin, and hematocrit. Because several of these measures experience temporal fluctuations related to the menstrual cycle, due to hydration state, etc, Li et al1 should have obtained and controlled for these variables. This is particularly important considering that Li et al1 based their LAEL of 1.28 ppm, in part on RBC count in female workers. Furthermore, these types of measures can be subject to interlaboratory variation; therefore, the authors should have included information on the laboratory control specimens, along with the mean, standard deviation, and coefficient of variation, that were evaluated with each batch of worker samples. Providing normal clinical ranges for measures would have aided with further evaluating these types of data. The authors should also have considered data clustering associated with the plant and the laboratory. Ignoring data dependency generally inflates the significance level. Given the availability of exposure estimates for individual workers, the regression model should have been fit with respect to individual exposure of 1-bromopropane instead of the group median, and the benchmark dose then applied. The impact of grouping workers into low, medium, and high exposure on the LAEL is less unclear but masks the uncertainty of the LAEL. The lack of uniform linear dose–response trend in many of the health parameters (see Li et al's Tables 3 and 6) with respect to group median exposure raises the question of how well the linear regression model fit each health outcome with median exposure. Fourth, Li et al1 reported that tibial motor distal latency and sural nerve conduction velocity were statistically significantly increased or decreased, respectively, in female workers. As with the endpoints discussed previously, providing normal clinical ranges (eg, tibial motor distal latency, normal range = 2.1 to 6.0 ms; sural nerve conduction velocity, normal range = 47.48 to 58.84 m/s)5,6 for these values would have been helpful with evaluating the clinical significance of the reported statistically significant changes. Furthermore, the other endpoint from which Li et al1 based their LAEL of 1.28 ppm, that is, vibration sense in the toe of female workers, was statistically significantly associated with the examining, unblinded, neurologist. Fifth, the authors reported that fatigue on the profile of mood states scale was statistically significantly different in exposed female workers compared with controls. They also reported that vigor and confusion were statistically significantly different when the workers were categorized on the basis of cumulative exposure. Li et al1 also reported statistically significant differences in male workers for the Santa Ana test (nonpreferred hand). Because reference values for individuals from China have been published,7 providing normal reference ranges would have aided readers discriminating between clinically significant versus statistically significant differences. Furthermore, it is noteworthy that the World Health Organization's neurobehavioral core test battery (NCTB), which includes the profile of mood states and the Santa Ana tests, are confounded by education. Anger et al8 reported that “[t]he NCTB is effective in testing adults with more than 12 years of education, it is less effective in some populations with 8-10 years of formal education, but it can not reliably test persons with less education.”8 In their previous description of the Yixing workers, Ichihara et al4 identified four controls with an elementary school–level education and 19 with a junior high school–level education. In the 1-bromopropane–exposed workers, four had an elementary school–level education, 12 had a junior high school–level education, six had a high school–level education, and 1 had university-level education. Li et al1 did not report the level of education of the respective workers. Because the NCTB may be susceptible to floor effects, utilizing matched controls with limited education will not alleviate this source of bias.8 Finally, Li et al1 stated: “[t]he authors have no financial interest related to this research.” However, the corresponding author (Dr Gaku Ichihara) served as an expert witness in a plaintiffs' suit against a furniture manufacturer that used 1-bromopropane as an adhesive.9 This disclosure might have suggested a particular viewpoint to the readership of the Journal of Occupational and Environmental Medicine. In conclusion, Li et al1 evaluated 1-bromopropane exposures in three workplaces, where the mechanical controls were inadequate, and where personal protective equipments were either not used or fell woefully short of accepted practices, resulting in potentially higher levels of exposure than reported. The study evaluated a number of metrics subject to interobserver variability, but neither the researchers nor the research subjects were blinded, which calls into question the validity of the observer-graded and self-reported measures. The authors identified statistically significant changes in a number of endpoints, which they attributed to 1-bromopropane. However, no reference ranges were provided. This is particularly important in studies of this type, where it is difficult to obtain true controls. Notwithstanding the foregoing issues, we feel that the true value of Li et al's1 contribution is the importance of emphasizing compliance with occupational safety standards to optimize worker safety. Carr J. Smith, PhD Health, Safety and Environment Division, Albemarle Corporation, Baton Rouge, La Giffe T. Johnson, PhD Raymond D. Harbison, PhD Center for Environmental and Occupational Risk Analysis and Management, College of Public Health University of South Florida, Tampa, Fla Yiliang Zhu, PhD Department of Epidemiology and Biostatistics, College of Public Health University of South Florida, Tampa, Fla Richard V. Lee, MD Department of Medicine and Obstetrics State University of New York, Buffalo, NY Marek Banasik, MD, PhD Institute of Public Health and Environmental Protection, Warsaw, Poland Todd Stedeford, PhD, JD Health, Safety and Environment Division Albemarle Corporation, Baton Rouge, La