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If someone had told me a couple of years ago that I should read a book on operational and regulatory challenges, I would have rolled my eyes in disbelief. How four years working in an agency with operational and regulatory functions can change your perspective. A lot. While there is still a role for broad based preventive programmes to promote certain goods, they are not a substitute for tasks to tackle specific harms, each with their own specific characteristics and texture. For the regulatory agency that organizes itself itself around a specific harm, this is often seen as a radical departure from the status quo; agencies seldom organize themselves around problems — they organize themselves around functions and processes.
A thought provoking read for anyone who deals broadly with harms and risks. Mar 09, Nicholas rated it really liked it. Since this book is more recent it covers a greater expanse of relevant problems and material of the past decade. Malcolm Sparrow masterfully confronts the challenges produced by public administration as it proceeds to move problem solving to the forefront. Harm-reduction theory becomes more applicable and practical in the modern world as non-compliance continues to grow. Aug 21, Joseph E. Very technical discussion, but a very interesting perspective on the flip-side of risk management.
Graphs and examples were very helpful to those of us not familiar with this area of program evaluation. I saw many applications to areas in which I am involved beyond those mentioned in the book. I look forward to applying some of the techniques I learned from this reading. Nov 28, Shawn rated it really liked it. Excellent book for policy analysts and regulations-makers, with practical approaches and examples. One star off for a discursive style and a vocabulary over the heads of the people who need to "get" this.
Jan 31, Jules Arntz-Gray rated it it was amazing. A must read for public policy regulators. Apr 15, Dale rated it it was amazing. This book was handed out at the Harvard Senior Executive Fellowship and is really good. The immediate impact was indeed an increase in sales volume, but the increase was accomplished in ways that were inconsistent with long-term organizational goals. The employees competed among themselves for customers and neglected important but unmeasured and unrewarded activities such as stocking and merchandising. Data distortion is another dangerous potential side effect of results controls.
If the measurement methods are not objective, then the employees whose performances are being measured might falsify the data or change the measurement methods, and, in so doing, undermine the whole organization's information system. Many of the ramifications of these unintended effects of control systems are not well understood, and their costs are very difficult to quantify. However, consideration of these effects is an important control-system design factor: they cannot be ignored.
Because feedback does not appear prominently in the preceding discussion, it is useful for clarification purposes to consider where feedback fits in, Control is necessarily future-oriented, as past performance cannot be changed, but analysis of results and feedback of variances can often provide a particularly strong addition to a control system.
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A prerequisite, of course, is the ability to measure results, so feedback can only be useful in the situations presented in boxes 1 and 3 of Figure 1. There are three reasons why feedback of past results is an important part of many control systems. First, feedback is necessary as reinforcement for a results-accountability system. Even if the feedback is not used to make input adjustments, it signals that results are being monitored. This can heighten employee awareness of what is expected of them and should help stimulate better performance. Second, in repetitive situations, measurement of results can provide indications of failure in time to make useful interventions.
This is shown in the simple feedback control model presented in Figure 2. When the results achieved are not satisfactory, the inputs, which include the specific actions and types of persons involved, can be changed to provide different results. Obviously, these input adjustments are more likely to improve results when there is a good understanding of how inputs relate to results; otherwise, the interventions are essentially experiments.
Third, analysis of how the results vary with different combinations of inputs might improve understanding of how the inputs relate to results. This process is depicted in loop A of Figure 3, a slightly more complicated feedback control model. If managers discover that certain specific actions produce consistently superior results, then it might be beneficial to inform employees of the specific actions that are expected of them, for example, by publishing these desired actions in a procedures manual. The greater the knowledge about how actions bring about results, the greater the possibilities of using a tight, specific-action-oriented control system.
Note that these latter two reasons for analyzing feedback — for making interventions and for learning — are only useful in situations that at least partially repeat themselves. If a situation is truly a one-time occurrence, such as a major divestiture or a unique capital investment, management has little use for feedback information. In these cases, by the time the results are available, it is too late to intervene, and a greater understanding of how results are related to inputs is not immediately useful.
There are other circumstances where feedback need not, and perhaps should not, be a part of a good control system. In many cases, although feedback control systems are not really feasible, they are used anyway. Cost considerations also commonly lead to decisions not to include feedback in a control system. The design, implementation, and maintenance of results-tracking information systems can often be very expensive.
Thus, it is not feasible to have feedback as part of every control system, nor is it necessarily desirable even when feasibility constraints are not present. As discussed at the beginning of this article, management control is a problem of human behavior. The challenge is to have each individual acting properly as often as possible. Thus, it seems logical to start the control-system design process by considering the personnel component of the organization by itself.
In some situations, well-trained, highly motivated personnel can be expected, with a high degree of certainty, to perform their jobs satisfactorily without any additional control steps being taken. A confident reliance on personnel controls is a very desirable situation because additional controls cost money and may have undesirable side effects.
If, however, management determines that personnel controls should be supplemented, the first step should be to examine the feasibility of the various control options. To do this, management must assess two factors: how much is known about which specific actions are desirable, and how well measurement can be accomplished in the important performance areas.
This feasibility test might immediately determine whether the controls that can be added should be oriented toward specific actions or results. Control can be made tighter by strengthening the controls in place, along the lines discussed earlier, or by implementing overlapping controls, such as controls over results and specific actions.
In most cases, management has some, but less than complete, knowledge of which specific actions are desirable and some, but not perfect, ability to measure the important result areas. This situation usually calls for implementation of both specific-action and results controls, with feedback loops to improve understanding of the relevant processes.
The above observations about control can be illustrated by describing how control of a sales force might work. Generally, personnel controls are some part of every sales force control system. Consider, for example, this statement by a sales and marketing consultant:. I think I can tell a good salesman just by being around him.
If the guy is experienced, confident, well-prepared, speaks well, maintains control of situations, and seems to have his time planned. I assume I have a good salesman. If a sales manager feels confident about all of the salespeople employed, he or she might wish to allow personnel controls to dominate the control system. This is likely, for example, in a small business with a sales force comprised solely of relatives and close friends. But most sales managers are not willing to rely exclusively on hiring and training good people. What controls should be added? The answer, of course, depends on the type of sales involved.
In a single-product, high-volume operation, the volume of sales generated is probably a good simple factor on which to base a results-oriented control system. It provides a reasonable, although not perfect, surrogate for long-range profitability, and the measurements are very inexpensive because the data are already gathered as a necessary input to the financial reporting system. The results-accountability system can then be completed by providing reinforcement in the form of sales commissions. This simple solution will also work where multiple products with varying profitabilities are involved, if the commission schedules are varied so that rewards are assigned in proportion to the profitability of the sales generated.
Consider, however, a situation where salespeople sell large-scale construction equipment and where sales come in very large but infrequent chunks.
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A commission-type, results-accountability system is still feasible. Measurement of results is not difficult and can be accurate to the penny. The amount of control provided, however, is not high because the measurements fail on the timeliness dimension. Because sales are infrequent, zero sales is not an unusual situation in any given month. Therefore, a salesperson could be drawing advances on hypothetical future commissions for many months without performing any of the desired promotional activities.
Two solutions are possible. One is to augment the commission system with some specific-action controls, such as activity reports. Some activities are probably known to be desirable, such as the number of hours worked and the quantity of calls made. If the product mix and market environment are fairly stable, then requiring and monitoring activity reports is not as costly as it might seem, because it could provide an important side benefit — an activity-oriented data base.
The patterns in this data base can be analyzed and compared with results over time to add to knowledge about which activities yield the best results. An alternate solution is to improve the results-accountability system. It might be possible to define some factors that are strong predictors of sales success, such as customer satisfaction with the salesperson or customer familiarity with the company's products. Measurement of these intangibles, of course, would have to be done by surveying customers.
Even though these measures do not directly assess the desired result area long-range profitability , and measurement is imprecise, they could provide a better focus for a results-oriented control system than a sales-generated measure because of the improvement in timeliness. Over time, it is likely that the choice of measures and measurement methodologies could be improved.
The advantage of this results-oriented solution over an action-oriented system is that it is more flexible and less constraining to the salespeople; they can continue to use styles best suited to their personalities. This article has taken a new look at the most basic organizational control problem — how to get employees to live up to the plans that have been established. In the course of discussion, the following major points were made:. An understanding of control can be an important input into many management decisions.
For example, control problems should be considered in making some types of investments. An investment in an operation in which control is very difficult — such as a highly specialized and technical area where control must depend heavily on personnel controls — is, by definition, risky. Thus, investments in such areas should promise high returns to compensate for this risk.
Similarly, control considerations should affect the design of the other parts of the management system. Consider, for example, the organizational structure. If independent areas of responsibility cannot be carved out as part of the organizational structure, results-accountability control systems will not work well because employees will not feel that their individual actions have a notice able effect on results. If independent areas of authority are not established, specific-action-accountability control systems cannot work.
This article has attempted to provide a new look at this basic, but often overlooked, management problem. The control area is decidedly complex, and there is much that is not known about how controls work and how employees respond to different types of controls. For example, it would be worthwhile to know more about how controls can be designed to maximize the amount of control provided while minimizing the cost in the form of employee feelings of lost autonomy.
They serve primarily to assess whether existing or anticipated odours should be classified as significant. The first possibility combines emission measurement with modelling and, strictly speaking, cannot be classified under the term air quality monitoring. In the third method, the human nose is used as the detector with significantly reduced precision as compared to physical-chemical methods. Details of inspections, measurement plans and assessing the results are contained, for example, in the environmental protection regulations of some German states. Simplified measurement procedures are sometimes used for preparatory studies screening.
Examples include passive samplers, test tubes and biological procedures. With passive diffusive samplers, the material to be tested is collected with freely flowing processes such as diffusion, permeation or adsorption in simple forms of collectors tubes, plaques and enriched in impregnated filters, meshes or other adsorption media. So-called active sampling sucking the sample air through a pump thus does not occur.
The enriched quantity of material, analytically determined according to definite exposure time, is converted into concentration units on the basis of physical laws e. The methodology stems from the field of occupational health personal sampling and indoor air measurement, but it is increasingly being used for ambient air pollutant concentration measurements. An overview can be found in Brown Detector tubes are often used for sampling and quick preparatory analysis of gases.
A certain test air volume is sucked through a glass tube that is filled with an adsorptive reagent that corresponds with the test objective. The contents of the tube change colour depending on the concentration of the material to be determined that is present in the test air.
Small testing tubes are often used in the field of workplace monitoring or as a quick procedure in cases of accidents, such as fires. They are not used for routine ambient air pollutant concentration measurements due to the generally too high detection limits and too limited selectivity. Detector testing tubes are available for numerous materials in various concentration ranges. Among the biological procedures, two methods have become accepted in routine monitoring. With the standardized lichen exposure procedure, the mortality rate of the lichen is determined over the exposure time of days.
Then the amount of growth is determined. Both procedures serve as summary determinations of air pollutant concentration effects. Around the world, the most varied types of air quality networks are utilized. A distinction should be drawn between measurement networks, consisting of automatic, computer-controlled measuring stations measurement containers , and virtual measurement networks, which only define the measurement locations for various types of air pollutant concentration measurements in the form of a preset grid.
Tasks and conceptions of measurement networks were discussed above. Continuously operating measurement networks are based on automatic measuring stations, and serve primarily for air quality monitoring of urban areas. Measured are air pollutants such as sulphur dioxide SO 2 , dust, nitrogen monoxide NO , nitrogen dioxide NO 2 , carbon monoxide CO , ozone O 3 , and to an extent also the sum of the hydrocarbons free methane, C n H m or individual organic components e. In addition, depending on need, meteorological parameters such as wind direction, wind speed, air temperature, relative humidity, precipitation, global radiation or radiation balance are included.
The measuring equipment operated in measurement stations generally consists of an analyser, a calibration unit, and control and steering electronics, which monitors the whole measuring equipment and contains a standardized interface for data collection. In addition to the measurement values, the measuring equipment supplies so-called status signals on errors and the operating status. The calibration of the devices is automatically checked by computer at regular intervals. As a rule, the measurement stations are connected with fixed data lines, dial connections or other data transfer systems to a computer process computer, workstation or PC, depending on the scope of the system in which the measurement results are entered, processed and displayed.
The measurement network computers and, if necessary, specially trained personnel monitor continuously whether various threshold limits are exceeded. In this manner critical air quality situations can be recognized at any time. This is very important, especially for monitoring critical smog situations in winter and summer photo-oxidants and for current public information.
Beyond the telemetric measurement network, other measuring systems for monitoring air quality are used to varying extents. Examples include occasionally partially automated measurement networks to determine:. A series of substances measured in this manner have been classified as carcinogens, such as cadmium compounds, PAHs or benzene.
Monitoring them is therefore particularly important. To provide an example of a comprehensive programme, table The objective of a manager of an air pollution control system is to ensure that excessive concentrations of air pollutants do not reach a susceptible target. Targets could include people, plants, animals and materials. In all cases we should be concerned with the most sensitive of each of these groups.
Air pollutants could include gases, vapours, aerosols and, in some cases, biohazardous materials. A well designed system will prevent a target from receiving a harmful concentration of a pollutant. Most air pollution control systems involve a combination of several control techniques, usually a combination of technological controls and administrative controls, and in larger or more complex sources there may be more than one type of technological control. Ideally, the selection of the appropriate controls will be made in the context of the problem to be solved.
What is the most susceptible target? Step 1: Define emissions. The first part is to determine what will be released from the stack.
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All potentially harmful emissions must be listed. The second part is to estimate how much of each material will be released. Without this information, the manager cannot begin to design a control programme. Step 2: Define target groups. All susceptible targets should be identified. This includes people, animals, plants and materials. In each case, the most susceptible member of each group must be identified. For example, asthmatics near a plant that emits isocyanates. Step 3: Determine acceptable exposure levels. If the pollutant is a material that has cumulative effects, such as a carcinogen, then long-term exposure levels annual must be set.
If the pollutant has short-term effects, such as an irritant or a sensitizer, a short-term or perhaps peak exposure level must be set. Step 1 identifies the emissions, and Step 3 determines the acceptable level. In this step, each pollutant is checked to ensure that it does not exceed the acceptable level. If it exceeds the acceptable level, additional controls must be added, and the exposure levels checked again.
This process continues until all exposures are at or below the acceptable level. Dispersion modelling can be used to estimate exposures for new plants or to test alternative solutions for existing facilities. Once the acceptable level has been established, background levels, and contributions from other plants must be subtracted to determine the maximum amount that the plant can emit without exceeding the acceptable exposure level.
If this is not done, and three plants are allowed to emit at the maximum, the target groups will be exposed to three times the acceptable level. Therefore, as long as some of the material is allowed to escape to the environment, there will be some risk to the target populations. In this case a no effect level cannot be set other than zero. Instead, an acceptable level of risk must be established. Usually this is set in the range of 1 adverse outcome in , to 1,, exposed persons. Some jurisdictions have done some of the work by setting standards based on the maximum concentration of a contaminant that a susceptible target can receive.
With this type of standard, the manager does not have to carry out Steps 2 and 3, since the regulating agency has already done this. Under this system, the manager must establish only the uncontrolled emission standards for each pollutant Step 1 , and then determine what controls are necessary to meet the standard Step 4. By having air quality standards, regulators can measure individual exposures and thus determine whether anyone is exposed to potentially harmful levels.
It is assumed that the standards set under these conditions are low enough to protect the most susceptible target group. This is not always a safe assumption. As shown in table For less commonly regulated materials this variation can be even larger 1. This is not surprising given that economics can play as large a role in standard setting as does toxicology. If a standard is not set low enough to protect susceptible populations, no one is well served.
Exposed populations have a feeling of false confidence, and can unknowingly be put at risk. The emitter may at first feel that they have benefited from a lenient standard, but if effects in the community require the company to redesign their controls, or install new controls, costs could be higher than doing it correctly the first time. One such method is best available control technology BACT. It is assumed that by using the best combination of scrubbers, filters and good work practices on an emission source, a level of emissions low enough to protect the most susceptible target group would be achieved.
Frequently, the resulting emission level will be below the minimum required to protect the most susceptible targets. This way all unnecessary exposures should be eliminated. Examples of BACT are shown in table BACT by itself does not ensure adequate control levels. Although this is the best control system based on gas cleaning controls and good operating practices, BACT may not be good enough if the source is a large plant, or if it is located next to a sensitive target.
Best available control technology should be tested to ensure that it is indeed good enough. The resulting emission standards should be checked to determine whether or not they may still be harmful even with the best gas cleaning controls. If emission standards are still harmful, other basic controls, such as selecting safer processes or materials, or relocating in a less sensitive area, may have to be considered.
Many jurisdictions establish emission standards that cannot be exceeded. Emission standards are based on emissions at the source. Usually this works well, but like BACT they can be unreliable. The levels should be low enough to maintain the maximum emissions low enough to protect susceptible target populations from typical emissions. However, as with best available control technology, this may not be good enough to protect everyone where there are large emission sources or nearby susceptible populations.
If this is the case, other procedures must be used to ensure the safety of all target groups. Both BACT and emission standards have a basic fault. They assume that if certain criteria are met at the plant, the target groups will be automatically protected. This is not necessarily so, but once such a system is passed into law, effects on the target become secondary to compliance with the law. BACT and source emission standards or design criteria should be used as minimum criteria for controls. If BACT or emission criteria will protect the susceptible targets, then they can be used as intended, otherwise other administrative controls must be used.
Controls can be divided into two basic types of controls - technological and administrative. Technological controls are defined here as the hardware put on an emission source to reduce contaminants in the gas stream to a level that is acceptable to the community and that will protect the most sensitive target.
Administrative controls are defined here as other control measures. Gas cleaning systems are placed at the source, before the stack, to remove contaminants from the gas stream before releasing it to the environment. The vapour is cooled and condensed to a liquid. Particle-laden gases are forced to change direction. A porous fabric removes particulates from the gas stream. The porous dust cake that forms on the fabric then actually does the filtration. The gas cleaner is part of a complex system consisting of hoods, ductwork, fans, cleaners and stacks.
The design, performance and maintenance of each part affects the performance of all other parts, and the system as a whole.
It should be noted that system efficiency varies widely for each type of cleaner, depending on its design, energy input and the characteristics of the gas stream and the contaminant. As a result, the sample efficiencies in table The variation in efficiencies is demonstrated with wet scrubbers in table Wet scrubber collection efficiency goes from As a result, gas cleaners must be matched to the specific gas stream in question. The use of generic devices is not recommended. When selecting and designing gas cleaning systems, careful consideration must be given to the safe disposal of the collected material.
If most of the contaminants are collected by the gas cleaning equipment there can be a hazardous waste disposal problem. In some cases the wastes may contain valuable products that can be recycled, such as heavy metals from a smelter, or solvent from a painting line. The wastes can be used as a raw material for another industrial process - for example, sulphur dioxide collected as sulphuric acid can be used in the manufacture of fertilizers.
Where the wastes cannot be recycled or reused, disposal may not be simple. Not only can the volume be a problem, but they may be hazardous themselves. For example, if the sulphuric acid captured from a boiler or smelter cannot be reused, it will have to be further treated to neutralize it before disposal. Dispersion can reduce the concentration of a pollutant at a target. However, it must be remembered that dispersion does not reduce the total amount of material leaving a plant.
A tall stack only allows the plume to spread out and be diluted before it reaches ground level, where susceptible targets are likely to exist. If the pollutant is primarily a nuisance, such as an odour, dispersion may be acceptable. However if the material is persistent or cumulative, such as heavy metals, dilution may not be an answer to an air pollution problem.
Dispersion should be used with caution. Local meteorological and ground surface conditions must be taken into consideration. For example, in colder climates, particularly with snow cover, there can be frequent temperature inversions that can trap pollutants close to the ground, resulting in unexpectedly high exposures.
Similarly, if a plant is located in a valley, the plumes may move up and down the valley, or be blocked by surrounding hills so that they do not spread out and disperse as expected. In addition to the technological systems, there is another group of controls that must be considered in the overall design of an air pollution control system.
For the large part, they come from the basic tools of industrial hygiene. One of the preferred occupational hygiene methods for controlling environmental hazards in the workplace is to substitute a safer material or process. If a safer process or material can be used, and harmful emissions avoided, the type or efficacy of controls becomes academic. It is better to avoid the problem than it is to try to correct a bad first decision. Examples of substitution include the use of cleaner fuels, covers for bulk storage and reduced temperatures in dryers.
This applies to minor purchases as well as the major design criteria for the plant. If only environmentally safe products or processes are purchased, there will be no risk to the environment, indoors or out.
If the wrong purchase is made, the remainder of the programme consists of trying to compensate for that first decision. If a low-cost but hazardous product or process is purchased it may need special handling procedures and equipment, and special disposal methods. As a result, the low-cost item may have only a low purchase price, but a high price to use and dispose of it.
Perhaps a safer but more expensive material or process would have been less costly in the long run. Controls are required for all the identified problems that cannot be avoided by substituting safer materials or methods. Emissions start at the individual worksite, not the stack. A ventilation system that captures and controls emissions at the source will help protect the community if it is properly designed. The hoods and ducts of the ventilation system are part of the total air pollution control system. A local ventilation system is preferred. It does not dilute the contaminants, and provides a concentrated gas stream that is easier to clean before release to the environment.
Gas cleaning equipment is more efficient when cleaning air with higher concentrations of contaminants. For example, a capture hood over the pouring spout of a metal furnace will prevent contaminants from getting into the environment, and deliver the fumes to the gas cleaning system. In table If pollutants are not caught at the source and are allowed to escape through windows and ventilation openings, they become uncontrolled fugitive emissions.
In some cases, these uncontrolled fugitive emissions can have a significant impact on the immediate neighbourhood. Isolation - locating the plant away from susceptible targets - can be a major control method when engineering controls are inadequate by themselves. This may be the only means of achieving an acceptable level of control when best available control technology BACT must be relied on. If, after applying the best available controls, a target group is still at risk, consideration must be given to finding an alternate site where sensitive populations are not present.
Isolation, as presented above, is a means of separating an individual plant from susceptible targets. Another isolation system is where local authorities use zoning to separate classes of industries from susceptible targets. Once industries have been separated from target populations, the population should not be allowed to relocate next to the facility.
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Work procedures must be developed to ensure that equipment is used properly and safely, without risk to workers or the environment. Complex air pollution systems must be properly maintained and operated if they are to do their job as intended. An important factor in this is staff training. Staff must be trained in how to use and maintain the equipment to reduce or eliminate the amount of hazardous materials emitted to the workplace or the community.
In some cases BACT relies on good practice to ensure acceptable results. A system based on real time monitoring is not popular, and is not commonly used. In this case, continuous emission and meteorological monitoring can be combined with dispersion modelling to predict downwind exposures. When the predicted exposures approach the acceptable levels, the information is used to reduce production rates and emissions.
This is an inefficient method, but may be an acceptable interim control method for an existing facility. The converse of this to announce warnings to the public when conditions are such that excessive concentrations of contaminants may exist, so that the public can take appropriate action. For example, if a warning is sent out that atmospheric conditions are such that sulphur dioxide levels downwind of a smelter are excessive, susceptible populations such as asthmatics would know not to go outside. Again, this may be an acceptable interim control until permanent controls are installed.
Real time atmospheric and meteorological monitoring is sometimes used to avoid or reduce major air pollution events where multiple sources may exist. When it becomes evident that excessive air pollution levels are likely, the personal use of cars may be restricted and major emitting industries shut down.
In all cases the effectiveness of the controls depends on proper maintenance; the equipment has to operate as intended. Not only must the air pollution controls be maintained and used as intended, but the processes generating potential emissions must be maintained and operated properly. An example of an industrial process is a wood chip dryer with a failing temperature controller; if the dryer is operated at too high a temperature, it will emit more materials, and perhaps a different type of material, from the drying wood.
An example of gas cleaner maintenance affecting emissions would be a poorly maintained baghouse with broken bags, which would allow particulates to pass through the filter. Housekeeping also plays an important part in controlling total emissions. Dusts that are not quickly cleaned up inside the plant can become re-entrained and present a hazard to staff.
If the dusts are carried outside of the plant, they are a community hazard. Poor housekeeping in the plant yard could present a significant risk to the community. Uncovered bulk materials, plant wastes or vehicle-raised dusts can result in pollutants being carried on the winds into the community. Keeping the yard clean, using proper containers or storage sites, is important in reducing total emissions.
A system must be not only designed properly, but used properly as well if the community is to be protected. A worst case example of poor maintenance and housekeeping would be the lead recovery plant with a broken lead dust conveyor. The dust was allowed to escape from the conveyor until the pile was so high the dust could slide down the pile and out a broken window. Local winds then carried the dust around the neighbourhood.
To design an air pollution control system, one must know what is being emitted. Not only the volume of gas, but the amount, identity and, in the case of particulates, size distribution of the material being emitted must be known. The same information is necessary to catalogue total emissions in a neighbourhood. After an air pollution control system has been purchased, it should be tested to ensure that it is doing the intended job. When emissions are continuously monitored, the data can be used to fine tune the air pollution control system, or the plant operation itself.
When regulatory standards include emission limits, emission sampling can be used to determine compliance or non-compliance with the standards. The type of sampling system used will depend on the reason for taking the samples, costs, availability of technology, and training of staff. Where there is a desire to reduce the soiling power of the air, improve visibility or prevent the introduction of aerosols into the atmosphere, standards may be based on visible emissions.
Visible emissions are composed of small particles or coloured gases. The more opaque a plume is, the more material is being emitted. This characteristic is evident to the sight, and trained observers can be used to assess emission levels. There are several advantages to using this method of assessing emission standards:. A much more rigorous sampling method calls for a sample of the gas stream to be removed from the stack and analysed.
Although this sounds simple, it does not translate into a simple sampling method. The sample should be collected isokinetically, especially when particulates are being collected. Isokinetic sampling is defined as sampling by drawing the sample into the sampling probe at the same velocity that the material is moving in the stack or duct.
This is done by measuring the velocity of the gas stream with a pitot tube and then adjusting the sampling rate so that the sample enters the probe at the same velocity. This is essential when sampling for particulates, since larger, heavier particles will not follow a change in direction or velocity. As a result the concentration of larger particles in the sample will not be representative of the gas stream and the sample will be inaccurate. A sample train for sulphur dioxide is shown in figure It is not simple, and a trained operator is required to ensure that a sample is collected properly.
If something other than sulphur dioxide is to be sampled, the impingers and ice bath can be removed and the appropriate collection device inserted. Extractive sampling, particularly isokinetic sampling, can be very accurate and versatile, and has several uses:. A simplified and automated sampling system can be connected to a continuous gas electrochemical, ultraviolet-photometric or flame ionization sensors or particulate nephelometer analyzer to continuously monitor emissions.
This can provide documentation of the emissions, and instantaneous operating status of the air pollution control system. Emissions can also be sampled in the stack. In this example, a beam of light is projected across the stack to a photcell. The particulates or coloured gas will absorb or block some of the light. The more material, the less light will get to the photocell. See figure By using different light sources and detectors such as ultraviolet light UV , gases transparent to visible light can be detected. These devices can be tuned to specific gases, and thus can measure gas concentration in the waste stream.
An in situ monitoring system has an advantage over an extractive system in that it can measure the concentration across the entire stack or duct, whereas the extractive method measures concentrations only at the point from which the sample was extracted. This can result in significant error if the sample gas stream is not well mixed. However, the extractive method offers more methods of analysis, and thus perhaps can be used in more applications. Since the in situ system provides a continuous readout, it can be used to document emissions, or to fine tune the operating system.
This article is intended to provide the reader with an understanding of currently available technology for approaching water pollution control, building on the discussion of trends and occurrence provided by Hespanhol and Helmer in the chapter Environmental Health Hazards. Water pollution refers to the qualitative state of impurity or uncleanliness in hydrologic waters of a certain region, such as a watershed.
The pollution process stresses the loss of purity through contamination, which further implies intrusion by or contact with an outside source as the cause. The term tainted is applied to extremely low levels of water pollution, as in their initial corruption and decay. Defilement is the result of pollution and suggests violation or desecration. As a reference for water quality, distilled waters H 2 O represent the highest state of purity. Waters in the hydrologic cycle may be viewed as natural, but are not pure.
They become polluted from both natural and human activities. Natural degradation effects may result from a myriad of sources - from fauna, flora, volcano eruptions, lightning strikes causing fires and so on, which on a long-term basis are considered to be prevailing background levels for scientific purposes. Human-made pollution disrupts the natural balance by superimposing waste materials discharged from various sources. Pollutants may be introduced into the waters of the hydrologic cycle at any point. For example: atmospheric precipitation rainfall may become contaminated by air pollutants; surface waters may become polluted in the runoff process from watersheds; sewage may be discharged into streams and rivers; and groundwaters may become polluted through infiltration and underground contamination.
Pollution is then superimposed on these waters and may therefore be viewed as an unnatural or unbalanced environmental condition. However groundwater pollution is also of major environmental impact and is discussed following the section on surface water pollution.