Ventilation for Control of the Work Environment / Edition 2 available in Hardcover
Ventilation for Control of the Work Environment / Edition 2
- ISBN-10:
- 047109532X
- ISBN-13:
- 9780471095323
- Pub. Date:
- 06/11/2004
- Publisher:
- Wiley
Ventilation for Control of the Work Environment / Edition 2
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Overview
This revised text includes a large amount of material on HVAC systems, and has been updated to reflect the changes in the Ventilation Manual published by ACGIH. It uses both English and metric units, and each chapter concludes with a problem set.
Product Details
| ISBN-13: | 9780471095323 |
|---|---|
| Publisher: | Wiley |
| Publication date: | 06/11/2004 |
| Edition description: | REV |
| Pages: | 440 |
| Product dimensions: | 6.38(w) x 9.63(h) x 1.03(d) |
About the Author
MICHAEL J. ELLENBECKER is Professor of Industrial Hygiene in the Department of Work Environment at the University of Massachusetts Lowell and the Director of the Toxics Use Reduction Institute. A Certified Industrial Hygienist, Dr. Ellenbecker received his ScD in environmental health sciences from Harvard.
ROBERT D. TREITMAN, a graduate of Brown University and the Harvard School of Public Health, has done extensive research and consulting in industrial hygiene and indoor air pollution. He is currently Vice President and co-owner of Softpro, Inc., in Waltham, Massachusetts.
CONTRIBUTORS-Professor Michael Flynn, University of North Carolina at Chapel Hill, has contributed a chapter introducing the application of computational methods to the study of ventilation. Martin Horowitz, an industrial hygiene pr actitioner at Analog Devices, has presented an overview of the techniques for the identification and control of contaminant reentry.
Read an Excerpt
Ventilation for Control of the Work Environment
By William A. Burgess Michael J. Ellenbecker Robert D. Treitman
John Wiley & Sons
Copyright © 2004 John Wiley & Sons, Inc.All right reserved.
ISBN: 0-471-09532-X
Chapter One
VENTILATION FOR CONTROL
The provision of a safe and healthful working environment entails three primary components: (1) awareness of potential hazards (recognition); (2) assessment of these hazards (evaluation); and (3) abatement of these hazards (control). Although a great deal of attention has been given to awareness and assessment, including toxicological research, epidemiological studies, standards setting, and environmental monitoring, the single most crucial element in the program-the reduction or elimination of the problem-has curiously been ignored. In a survey of industrial hygiene literature, 40% of the papers published in one journal over a 3 1/2-year period addressed monitoring, 24% addressed physical effects and epidemiology, 8% covered personal protection, and less than 8% were devoted to environmental control (Hammond, 1980). As Hammond (1980) states:
One would hope in 10-20 yr time to be able to look back and find the monitoring and the environmental control rankings reversed, with the ongoing and necessary epidemiology holding its central position. This would place monitoring nearer its correct position as a back up to good environmentalcontrol.
A similar review of the industrial hygiene literature conducted more than a decade later (Burgess, 1993) demonstrated little improvement in the ranking of environmental control papers. To place the use of ventilation in perspective with other mechanisms for environmental control, an introduction to those mechanisms follows.
1.1 CONTROL OPTIONS
The methods used to control worker exposure to harmful materials or conditions in the occupational environment have been categorized in a number of ways as shown in Table 1.1. In nearly all cases, the most effective approach is the combination of controls into an integrated package. The elimination of an offending agent from the workplace, accompanied, if necessary, by its replacement with a safer material, should be considered first in any effort to control the environment. The substitution of less hazardous materials has become quite common in industry, as knowledge of dangers from certain materials becomes available. For example, hydrocarbon-solvent-based paints are being replaced by water-based paints. Purchasers of some organic solvents are specifying that these solvents contain only trace amounts of benzene contamination. The principle of elimination and substitution applies to equipment and processes as well as materials. Newer machinery is often designed to minimize dust generation and release, for example. Processes can be modified to incorporate contaminant reduction techniques. The introduction of a raw material in pellet form in rubber compounding is less likely to generate dust than the same material presented as a powder.
If it is not feasible to eliminate the contaminant from the workplace, another approach is to isolate it from the workers who frequent the area. Distance and physical barriers, preferably around the process, but possibly around the workers, can provide protection. In either case, this method of control is usually accompanied by a ventilation system. When the process is isolated, the emphasis is on exhausting the contaminated air from the process. In contrast, when the worker is isolated, the emphasis should be on supplying clean air to the worker's station.
Administrative controls such as worker rotation through hazardous areas can also be implemented. In the nuclear power industry, exposure to radiation is limited on a 3-month as well as an annual basis. Any worker achieving the maximum permissible exposure before the end of the pertinent period is transferred to a low-radiation work area for the balance of time. In hot environments, workers should be allowed to rest in a cool area on a frequent basis throughout the workshift to allow time for the body to recover from the thermal stress. Other administrative controls include biological monitoring, worker education, and equipment maintenance. In all cases, administrative controls should be combined with attempts to reduce the hazard through engineering controls.
The focus of this volume, the use of ventilation, is ubiquitous in the modern workplace. Virtually every industrial and commercial facility contains some form of ventilation system for environmental control. The intent may be comfort (temperature, humidity, odors), safety (flammable vapors), or health (toxic particles, gases and vapors, airborne contagions).
The last resort for preventing exposures to toxic chemicals is personal protection, in the form of respirators and protective garments. Respiratory protection is used when all other controls are inadequate or when the possible failure of those controls would produce a hazardous situation.
1.2 VENTILATION FOR CONTROL OF AIR CONTAMINANTS
A review of the literature reveals that there was a great deal of interest in the theoretical and engineering aspects of industrial ventilation in the late 1930s and the early 1940s. The pace of the activity increased with the onset of World War II, with many of the articles covering industrial processes with direct defense applications, such as shipyard welding, rubber life-raft manufacturing, and synthetic-rubber production. It was during this time that pioneering industrial hygienists and engineers such as Phillip Drinker, Theodore Hatch, Allen Brandt, Constantin Yaglou, Leslie Silverman, W. C. L. Hemeon, and J. M. DallaValle were all very active. Much of the information was eventually incorporated into the first edition of the Industrial Ventilation Manual, published by the American Conference of Governmental Industrial Hygienists (ACGIH) in 1951.
The New York State Department of Labor's Division of Industrial Hygiene and Safety Standards published a Monthly Review beginning in the 1920s. Articles appearing in the late 1940s and early 1950s presented several theoretical and practical guides for the use of ventilation for contaminant control. In the mid-1950s, the Division of Occupational Health of the Michigan Department of Health began publication of Michigan's Occupational Health, a newsletter by industrial hygienists and other occupational health professionals that contained numerous articles on practical applications of industrial ventilation. The Michigan Department of Health contributions by James Barrett, Bernie Bloomfield, and Marvin Schuman were joined by those of George Hama, Knowlton Caplan, and Ken Robinson and others to provide core material for the ACGIH's manual as it evolved in the 1950s.
Ventilation engineers categorize systems as being either general (dilution) or local exhaust ventilation systems. The most basic form of ventilation is general or dilution ventilation, consisting simply of an exhaust fan pulling air out of the workplace and exhausting it to the outdoors. A general ventilation system may include a replacement air system, replacement-air distribution ducting, and in rare situations, air-cleaning equipment on the exhaust stream. As shown in Table 1.2, general exhaust ventilation can be used if the contaminant(s) of interest is not highly toxic and if the rate of generation is predictable. It is not usually the system of first choice to the ventilation designer, but may be the most practical for a situation where there are many contaminant sources scattered throughout the workplace or where the sources are mobile (e.g., forklift trucks in a warehouse).
Local exhaust ventilation (LEV) implies an attempt to remove the contaminant at or near the point of release, thus minimizing the opportunity for the contaminant to enter the workplace air. The ability of a LEV system to accomplish this task is dependent on its proper design, construction, and operation. The nominal LEV system includes an exhaust hood, ducting, a fan, and an exhaust outlet. As with general exhaust ventilation, additional components, such as replacement air systems and air-cleaning devices, may (and should) be included. Local exhaust systems are used in a wide variety of settings, from research laboratory hoods to commercial kitchens to foundries. LEV systems can, and should, be used in the vast majority of situations in preference over general exhaust.
In addition to the nominal system described above, there are a number of special types of LEV systems, used for particular applications and types of equipment. A low-volume/high-velocity system involves the positioning of a small hood adjacent to, or surrounding, the point of contaminant generation. A relatively high capture velocity [10,000 fpm (50 m/s) to 15,000 fpm (76 m/s)] is attained at a low airflow [60 cfm (0.03 [m.sup.3]/s) to 150 cfm (0.07 [m.sup.3]/s)] by designing a small hood opening. These systems operate at much higher static pressures than traditional ventilation systems but have the distinct advantage of minimizing the total exhaust flow, thus reducing the need for expensive replacement air.
Push-pull hoods are used on wide, open-surface tanks where exhaust slots on either side would be inadequate to draw air from the center of the tank. Instead, one side of the tank is fitted with a source of supply air while the other remains as an exhaust. A jet of air from the supply side is blown across the tank surface and collected in the exhaust hood.
1.3 VENTILATION APPLICATIONS
The design goal of industrial ventilation is to protect the worker from airborne contamination in the workplace. To the newcomer this may suggest installing a system that will reduce exposure below the Permissible Exposure Guidelines or an appropriate action level. This is not the case. The professional will design the system to meet the goal of "as low as reasonably practical." Within this control approach the effectiveness of the major ventilation techniques is shown in Table 1.2. There is no agreement on the position of low-volume-high-velocity systems since its effectiveness varies greatly depending on the degree of integration with the tool.
Soule (1991) reviews the application of the two major ventilation control approaches, dilution and local exhaust ventilation (Table 1.3). In most industries dilution is not the primary ventilation control approach for toxic materials. It is accepted that local exhaust ventilation will not provide total capture of contaminant and dilution ventilation is frequently applied to collect losses from such systems. In addition, it is used for multiple, dispersed, low-toxicity releases.
The specific design methods for both general exhaust ventilation and local exhaust ventilation are available, however an important predesign phase identified by Burton (1997) as problem characterization is frequently given little attention (Table 1.4). This is a topic that can be best addressed by an industrial hygienist who can provide data on emissions, air patterns, and worker movement and actions.
If the process is new, a videotape of a similar operation with the same unit operations may be available. The best of all worlds would be the availability of a video-concentration tape. If the facility is a duplicate of one in the company the industrial hygienist should visit the operation with the ventilation designer. Frequently the designer is an outside contractor. In this case it is important that the problem characterization approach be followed and an information package be provided the designer.
The precautions that should be reflected in the design have been discussed in detail elsewhere, but should include worker interface, access for maintenance, and routine testing. Computer-aided manufacturing/design (CAM/CAD) technology now permits precise placement of equipment and ductwork so that ad hoc placement by the installer should be a thing of the past. As discussed earlier, it may be worthwhile to "mock up" a specific design solution prior to final design and construction. This is especially true when a large number of identical workstations are to be installed.
General cautions are appropriate on the use of available design data for control of industrial operations. The ACGIH Industrial Ventilation Manual provides the most comprehensive selection of design plates for general industry ACGIH (2001). Each of these plates provides four specific design elements: hood geometry, airflow rate, minimum duct velocity, and entry loss. The missing element is the performance of the hood in terms of percent containment or capture efficiency.
Although ventilation control designs on standard operations in the mature industries have been published, performance has rarely been reported. It is important to evaluate performance by diagnostic air sampling both to ensure that the worker is protected and to prevent overdesign. The latter was shown to be the case in the design for control of a push-pull system for open-surface tanks (Sciola, 1993). A mock-up of one tank demonstrated that satisfactory control could be achieved at minimal airflow. Operating at the reduced airflow rate saved $100,000 in installation costs and $263,000 in annual operating costs.
1.4 CASE STUDIES
One of the more clear examples of the effectiveness of ventilation as a prime factor in the reduction of an industrial disease problem is the case of the Vermont granite workers exposed to silica in the first half of the twentieth century. Around the beginning of the century, pneumatic tools were introduced into the granite-cutting industry. These tools were capable of generating large amounts of airborne dust, much more than had been produced with the hand tools used previously. The net result of this new technology was a dramatic rise in the death rate attributable to tuberculosis among granite cutters using these new tools, at a time when the national tuberculosis mortality rate was steadily declining (Fig. 1.1). The association of the mortality rate with dust level was quite dramatic (Fig. 1.2). The pneumatic tool users and cutters (group A) had the highest dust levels and the highest death rates. Lower concentrations and mortality rates were observed in group B (surface machine operators) and group C (those exposed to general plant dust). The lowest mortality rates were observed in group D, workers who were exposed to less-than-average dust concentrations, such as personnel associated with sandblasting, an operation that had always been done with local exhaust ventilation. These data led the state of Vermont to require workplace controls in the granite-cutting sheds to reduce the dust concentration to below 10 million particles per cubic foot (mppcf). In the late 1930s, local exhaust ventilation was installed as the primary workplace control. The immediate effect on the dust concentrations was a 10 to 80% reduction between 1937 and 1940 (Fig. 1.3).
Continues...
Excerpted from Ventilation for Control of the Work Environment by William A. Burgess Michael J. Ellenbecker Robert D. Treitman Copyright © 2004 by John Wiley & Sons, Inc.. Excerpted by permission.
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Table of Contents
List of Units xiiiPreface xv
1 Ventilation for Control 1
1.1 Control Options 2
1.2 Ventilation for Control of Air Contaminants 3
1.3 Ventilation Applications 5
1.4 Case Studies 7
1.5 Summary 9
References 11
2 Principles of Airflow 12
2.1 Airflow 13
2.2 Density 13
2.3 Continuity Relation 14
2.4 Pressure 16
2.4.1 Pressure Units 16
2.4.2 Types of Pressure 17
2.5 Head 18
2.6 Elevation 20
2.7 Pressure Relationships 22
2.7.1 Reynolds Number 24
2.8 Losses 26
2.8.1 Frictional Losses 26
2.8.2 Shock Losses 28
2.9 Losses in Fittings 30
2.9.1 Expansions 30
2.9.2 Contractions 32
2.9.3 Elbows 35
2.9.4 Branch Entries (Junctions) 36
2.10 Summary 38
List of Symbols 38
Problems 39
3 Airflow Measurement Techniques 43
3.1 Measurement of Velocity by Pitot–Static Tube 45
3.1.1 Pressure Measurements 47
3.1.2 Velocity Profile in a Duc 50
3.1.3 Pitot–Static Traverse 57
3.1.4 Application of the Pitot–Static Tube and Potential Errors 60
3.2 Mechanical Devices 61
3.2.1 Rotating Vane Anemometers 61
3.2.2 Deflecting Vane Anemometers (Velometer) 68
3.2.3 Bridled Vane Anemometers 71
3.3 Heated-Element Anemometers 72
3.4 Other Devices 75
3.4.1 Vortex Shedding Anemometers 75
3.4.2 Orifice Meters 76
3.4.3 Venturi Meters 76
3.5 Hood Static Pressure Method 77
3.6 Calibration of Instruments 79
3.7 Observation of Airflow Patterns with Visible Tracers 80
3.7.1 Tracer Design 81
3.7.2 Application of Visible Tracers 84
List of Symbols 85
References 86
Manufacturers of Airflow Measuring Instruments 87
Manufacturers of Smoke Tubes 87
Problems 87
4 General Exhaust Ventilation 90
4.1 Limitations of Application 91
4.2 Equations for General Exhaust Ventilation 93
4.3 Variations in Generation Rate 99
4.4 Mixing 100
4.5 Inlet Outlet Locations 101
4.6 Other Factors 102
4.7 Comparison of General and Local Exhaust 105
List of Symbols 106
References 106
Problems 107
5 Hood Design 108
5.1 Classification of Hood Types 109
5.1.1 Enclosures 109
5.1.2 Exterior Hoods 110
5.1.3 Receiving Hoods 115
5.1.4 Summary 116
5.2 Design of Enclosing Hoods 116
5.3 Design of Exterior Hoods 120
5.3.1 Determination of Capture Velocity 120
5.3.2 Determination of Hood Airflow 125
5.3.3 Exterior Hood Shape and Location 135
5.4 Design of Receiving Hoods 135
5.4.1 Canopy Hoods for Heated Processes 135
5.4.2 Hoods for Grinding Operations 138
5.5 Evaluation of Hood Performance 141
List of Symbols 142
References 142
Appendix: Exterior Hood Centerline Velocity Models 144
Problems 148
6 Hood Designs for Specific Applications 151
6.1 Electroplating 152
6.1.1 Hood Design 152
6.1.2 Airflow 155
6.2 Spray Painting 159
6.2.1 Hood Design 159
6.2.2 Airflow 163
6.3 Processing and Transfer of Granular Material 165
6.4 Welding, Soldering, and Brazing 169
6.5 Chemical Processing 177
6.5.1 Chemical Processing Operations 178
6.6 Semiconductor Gas Cabinets 187
6.6.1 Entry Loss 190
6.6.2 Optimum Exhaust Rate 191
6.7 Low-Volume High-Velocity Systems for Portable Tools 192
Example 6.1 Calculation of Exhaust Rate for Open-Surface Tanks 199
Example 6.2 Design of a Low-Volume High-Velocity Exhaust System 200
List of Symbols 201
References 202
7 Chemical Laboratory Ventilation 204
7.1 Design of Chemical Laboratory Hoods 205
7.1.1 Vertical Sliding Sash Hoods 205
7.1.2 Horizontal Sliding Sash Hoods 209
7.1.3 Auxiliary Air Supply Hoods 212
7.2 Face Velocity for Laboratory Hoods 214
7.3 Special Laboratory Hoods 216
7.4 Laboratory Exhaust System Features 217
7.4.1 System Configuration 217
7.4.2 Construction 218
7.5 Factors Influencing Hood Performance 220
7.5.1 Layout of Laboratory 220
7.5.2 Work Practices 222
7.6 Energy Conservation 224
7.6.1 Reduce Operating Time 224
7.6.2 Limit Airflow 225
7.6.3 Design for Diversity 227
7.6.4 Heat Recovery 227
7.6.5 Ductless Laboratory Hoods 227
7.7 Performance of Laboratory Hoods 228
7.8 General Laboratory Ventilation 229
References 229
Problems 230
8 Design of Single-Hood Systems 232
8.1 Design Approach 233
8.2 Design of a Simple One-Hood System (Banbury Mixer Hood) 234
8.3 Design of a Slot Hood System for a Degreasing Tank 241
8.3.1 Loss Elements in a Complex Hood 241
8.3.2 Degreaser Hood Design Using Velocity Pressure Calculation Sheet (Example 8.2) 245
8.4 Pressure Plot for Single-Hood System 247
List of Symbols 247
Example 8.1 Banbury Mixer System Designed by the Velocity Pressure Method 248
Example 8.2 Degreaser System Designed by the Velocity Pressure Method 250
References 251
Appendix: Metric Version of Example 8.1 252
Problems 252
9 Design of Multiple-Hood Systems 254
9.1 Applications of Multiple-Hood Systems 254
9.2 Balanced Design Approach 256
9.3 Static Pressure Balance Method 260
9.3.1 Foundry Cleaning Room System (Example 9.1) 260
9.3.2 Electroplating Shop (Example 9.2) 262
9.4 Blast Gate Balance Method 265
9.5 Other Computational Methods 265
List of Symbols 266
Example 9.1 Foundry Cleaning Room Designed by Static Pressure Balance Method 267
Example 9.2 Electroplating Shop System Designed by Static Pressure Balance Method 272
References 278
Additional Reading 279
Appendix: Metric Version of Example 9.1 280
10 Fans and Blowers 282
10.1 Types of Air Movers 283
10.1.1 Axial Flow Fans 283
10.1.2 Centrifugal Fans 285
10.1.3 Air Ejectors 287
10.2 Fan Curves 288
10.2.1 Static Pressure Curve 289
10.2.2 Power Curve 291
10.2.3 Mechanical Efficiency Curve 293
10.2.4 Fan Laws 295
10.2.5 Relationship between Fan Curves and Fan Tables 297
10.3 Using Fans in Ventilation Systems 298
10.3.1 General Exhaust Ventilation Systems 298
10.3.2 Local Exhaust Ventilation Systems 300
10.4 Fan Selection Procedure 305
List of Symbols 308
References 309
Problems 309
11 Air-Cleaning Devices 311
11.1 Categories of Air-Cleaning Devices 312
11.1.1 Particle Removers 312
11.1.2 Gas and Vapor Removers 322
11.2 Matching the Air-Cleaning Device to the Contaminant 325
11.2.1 Introduction 325
11.2.2 Device Selection 326
11.3 Integrating the Air Cleaner and the Ventilation System 326
11.3.1 Gravity Settling Devices 330
11.3.2 Centrifugal Collectors 330
11.3.3 Filters 331
11.3.4 Electrostatic Precipitators 334
11.3.5 Scrubbers 334
11.3.6 Gas and Vapor Removers 335
List of Symbols 336
References 337
Problems 337
12 Replacement-Air Systems 338
12.1 Types of Replacement-Air Units 340
12.2 Need for Replacement Air 341
12.3 Quantity of Replacement Air 342
12.4 Delivery of Replacement Air 344
12.4.1 Replacement-Air System 1 (RAS-1), Melting Furnaces 349
12.4.2 Replacement-Air System 2 (RAS-2), Floor Casting 349
12.4.3 Replacement-Air System 3 (RAS-3), Sand Handling 350
12.4.4 Replacement-Air System 4 (RAS-4), Shakeout 351
12.5 Replacement Air for Heating 352
12.6 Energy Conservation and Replacement Air 353
12.7 Summary 356
References 356
13 Quantification of Hood Performance 358
13.1 Hood Airflow Measurements 359
13.2 Hood Capture Efficiency 360
13.2.1 Influence of Cross-Drafts on Hood Performance 361
13.2.2 Relationship between Airflow Patterns and Capture Efficiency 363
13.2.3 Shortcomings of the Centerline Velocity Approach 370
13.3 Use of Capture Efficiency in Hood Design 372
List of Symbols 372
References 373
14 Application of Computational Fluid Dynamics to Ventilation System Design 374
14.1 Introduction 374
14.2 Methods 376
14.2.1 Grid-Based Methods 377
14.2.2 Grid-Free Methods 378
14.3 Applications 379
14.3.1 Historical Perspectives 379
14.3.2 Current Progress 380
14.4 Issues on the Use of Computational Fluid Dynamics 386
14.5 Commercial Codes: Public-Domain Information 387
References 387
Appendix 389
15 Reentry 391
15.1 Airflow around Buildings 393
15.2 Measurement of Reentry 396
15.3 Calculation of Exhaust Dilution 401
15.4 Scale Model Measurement 404
15.5 Design to Prevent Reentry 406
15.5.1 Stack Height Determination 407
15.5.2 Good Engineering Practices for Stack Design 408
List of Symbols 412
References 413
Problems 415
Index 417
What People are Saying About This
"…clearly a definitive first class publication on industrial ventilation…if your goal is to expand your knowledge of ventilation this a great place to start." (Chemical Health and Safety, January-February 2005)