MINE VENTILATION AND AIR CONDITIONING

MINE VENTILATION AND AIR CONDITIONING

THIRD EDITION

Howard L. Hartman The University of Alabama (Emeritus)

Jan M. Mutmansky The Pennsylvania State University

Raja V. Ramani The Pennsylvania State University

Y. J. Wang West Virginia University

A WILEY-INTERSCIENCE PUBLICATION

JOHN WILEY & SONS, INC. Nevy York • Chichester • Weinheim • Brisbane • Singapore • Toronto

This book is printed on acid-free paper. @

Copyright © 1997 by John Wiley & Sons, Inc. All rights reserved.

Published simultaneously in Canada.

No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4470. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., Ill River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008.

Library of Congress Cataloging in Publication Data: Mine ventilation and air conditioning / Howard L. Hartman ... [et

al.].—3rd ed. p. cm.

Rev. ed. of: Mine ventilation and air conditioning / Howard L. Hartman. 2nd ed. 1991.

"A Wiley-Interscience publication." Includes bibliographical references and index. ISBN 0-471-11635-1 (cloth : alk. paper) 1. Mine ventilation. 2. Air conditioning. I. Hartman, Howard L.

TN301.M554 1997 622'.42—dc21 97-547

Printed in the United States of America

17 16 15 14

To our wives,

Bonnie, Diane, Geetha, and Janet

whose support, understanding, and patience on the home front enabled

us to write this book.

CONTENTS

Preface ix

Acknowledgments xi

List of Mathematical Symbols xiii

List of Map Symbols xvii

PART I INTRODUCTION 1

1. Environmental Control of the Mine Atmosphere 3

2. Properties and Behavior of Air 12

PART II MINE AIR-QUALITY CONTROL 27

3. Mine Gases 29

4. Dusts and Other Mine Aerosols 77

PART III MINE VENTILATION 133

5. Airflow through Mine Openings and Ducts 135

6. Ventilation Measurements and Surveys 178

7. Mine Ventilation Circuits and Networks 240

8. Natural Ventilation 293

9. Air-Moving Equipment 320

10. Fan Application to Mines 355

11. Auxiliary Ventilation and Controlled Recirculation 405

12. Economics of Airflow 431

13. Coal Mine Ventilation Systems 455

vii

VÜi CONTENTS

14. Metal Mine Ventilation Systems 524

15. Control of Mine Fires and Explosions 562

PART IV MINE AIR CONDITIONING 583

16. Heat Sources and Effects in Mines 585

17. Mine Air Conditioning Systems 619

APPENDIXES

A. Reference Tables and Figures 663

B. SI Units in Mine Ventilation 676

C. Laboratory Experiments 682

D. Computer Applications and Software 686

References 690 Answers to Selected Problems 713

INDEX 721

PREFACE

That this book has enjoyed a modicum of success and evolved into a third edition was hardly anticipated when the original work was published in 1961. The second edition, issued in 1982, was a group effort by 25 contributors and modernized and expanded the coverage. When it was decided to revise the book again, four of us agreed to undertake the task.

Our objectives in the third edition are largely the same as before: (1) to present an integrated engineering design approach to mine ventilation and air conditioning, (2) to advance an understanding of comprehensive environ-mental control of the mine atmosphere, and (3) to advocate total mine air conditioning through simultaneous control of the quality, quantity, and tem-perature-humidity of the underground atmospheric environment.

What may differ in this revision is the emphasis on an undergraduate treatment of the subject matter. We have intentionally restricted the scope and level of the coverage so that students can cover the material in one semester, assuming a background in the basic and engineering sciences and introductory mining engineering courses.

We have also directed the book to practitioners of mine ventilation in the field. It should provide adequate depth and breadth to those who design or operate mines, with responsibility for environmental engineering and espe-cially for the health and safety of miners who rely on the underground atmo-sphere for survival.

To be responsive to current trends, we have again made use of dual mathe-matical units (English and SI) throughout.

We are indebted to our colleagues who contributed to the second edition; with their permission, we have drawn liberally in this revision from their earlier work. Additionally, sources in the current literature, manufacturers, and practicing ventilation engineers have generously provided state-of-the-art knowledge for our efforts.

To my three coauthors in this endeavor—all Penn State associates or former students of mine—I give warm thanks. To them belongs any credit for the lasting contribution this volume may make to our profession. In ac-knowledgment of our common educational roots, we have assigned all royal-ties from this book (as we also did with the second edition) to endow a mining engineering scholarship at our alma mater.

Sacramento, California HOWARD L. HARTMAN

IX

ACKNOWLEDGMENTS

The following persons authored chapters that appeared in the Second Edition of this book (1982) and gave permission to the present authors to draw on that material as appropriate. Their contributions to the Third Edition are gratefully acknowledged.

James L. Banfield, Jr. (deceased) Formerly of the Mine Safety and Health Administration H. Douglas Dahl Eastern Associated Coal Company Rodolfo V. de la Cruz University of Wisconsin at Madison Ralph K. Foster Retired, Formerly of the Mine Safety and Health Administration Y. S. Kim Private Consultant Richard J. Kline Mine Safety and Health Administration Thomas Novak The University of Alabama Richard L. Sanford The University of Alabama Stanley C. Suboleski A. T. Massey Coal Company Peter M. Turcic Mine Safety and Health Administration

Floyd C. Bossard Floyd C. Bossard & Associates, Inc. Robert W. Dalzell Retired, Formerly of the Mine Safety and Health Administration C. Frederick Eben Retired, Formerly of Bethlehem Steel Corporation Bruce R. Johnson Zephyrus Mining Consultants Inc. John D. Kalasky (deceased) Formerly of Island Creek Coal Company Edward J. Miller Mine Safety and Health Administration Thomas J. O'Neil Cleveland Cliffs Inc. Madan M. Singh Engineers International, Inc. Pramod C. Thakur Consol Inc. Richard W. Walli Private Consultant Edwin B. Wilson Bethlehem Steel Corporation

The present authors also extend thanks to John E. Urosek, Chief, Ventila-tion Division, Mine Safety and Health Administration, and his colleagues who read and provided technical advice on Chapter 15, Control of Mine Fires and Explosions.

xi

LIST OF MATHEMATICAL SYMBOLS

Mathematical symbols associated with the literature and practice of mine ventilation have evolved with time. Originally, they were based on American National Standards Institute (ANSI) codes, but these standards have fallen into disuse over the years. The symbols employed in this book are represen-tative of the ones customarily employed in mine ventilation in the United States and have been adopted because of their clarity, consistency, and re-cognizability.

Symbol Letters

A Area, ft2 (m2) a Radius, ft (m) B Characteristic gas flow constant of coal seam, atm" ' Bg concentration of gas in air, % or fraction b Modified seam characteristic (dimensionless); width, ft (m) C Cost, $; concentration of tracer gas, %; concentration of methane

in coal, ft3/ft3 (m3/m3) CCI Anemometer correction factor, ft/min (fpm) (m/s) Cc Coefficient of contraction (dimensionless); Cunningham correction

factor (dimensionless) C, Thermal conductance of rock, Btu/hft2oF (Wm2oC) CF Altimeter correction factor (dimensionless) c Specific heat, Btu/Ib°F (kJ/kg°C); unit cost, $/ft3 ($/m3) D Diameter, ft (m); coefficient of diffusion or diffusivity, ft2/h (m2/s) DR Altimeter density ratio (dimensionless) d Depth (or height), ft (m) E Exposure concentration, mg/m3; excavation cost, $/ft ($/m) of ad-

vance Ec Effective combustible parameter, % £, Effective inert parameter, % F Sensible-heat factor (dimensionless); force, lb (N) / Coefficient of friction (dimensionless) G Weight flow rate, Ib/h (kg/s) G„, Liquid weight flow rate, lb/h (kg/s) g Acceleration due to gravity = 32.174 ft/s2 (9.807 m/s2)

xiii

XIV LIST OF MATHEMATICAL SYMBOLS

H Difference in head, inches (in.) water (mm or Pa) Hf Friction head loss, in. water (mm or Pa) H, Head loss, in. water (mm or Pa) H,„ Mechanical ventilation head, in. water (mm or Pa) H„ Natural ventilation head, in. water (mm or Pa) // , Static head, in. water (mm or Pa) H, Total head, in. water (mm or Pa) H„ Velocity head, in. water (mm or Pa) Hx Shock head loss, in. water (mm or Pa) Hz Elevation or potential head, in. water (mm or Pa) h Enthalpy, Btu/lb (kJ/kg) K Cooling power, Btu/hft2 (W/m2) hcorr Enthalpy correction, Btu/lb (kJ/kg) hscp Specific cooling power, Btu/hft2 (W/m2) / Internal energy, Btu/lb (kJ/kg); inhalation rate, m3/h ICO Index of carbon monoxide or Graham's ratio (dimensionless) i Sound intensity, dB K Friction factor, lbmin2/ft4 (kg/m3) K, Compression friction factor, lb2in.min2/ft7 (kg2/s2m4) k Conductivity, Btu/hft°F (W/m°C); constant of proportionality (di-

mensionless); permeability of coal, miilidarcies (m2) L Length (or distance), ft (m) Le Equivalent length due to shock loss, ft (m) Lp Sound pressure level, dB L„ Sound power level, dB M Metabolism rate, Btu/h Mf, Mass of tracer gas, lb (kg) M, Volume of gas desorbed in given time, ft3/h (m3/s) m Molecular weight (dimensionless); radius ratio = rib (dimen-

sionless) N Number or ratio (dimensionless) Na Number of airways in parallel Nh Number of branches in network (dimensionless) Nt Layering number (dimensionless) N„, Network degree or number of meshes in network (dimensionless) Nn Number of nodes in a network (dimensionless) NRe Reynolds number (dimensionless) NVE Natural ventilation energy, ft (m) NVP Natural ventilation pressure, in. water (Pa) n Rotational speed, r/min (rpm); process index (dimensionless) O Perimeter, ft (m) Oe Equivalent orifice, ft2 (m2) P Probability (dimensionless) Pa Air power, hp (kW) Pi Electrical input power, hp (kW)

LIST OF MATHEMATICAL SYMBOLS XV

P,„ Mechanical power , bhp (kW) P„ Sound power , W p Root-mean-square sound p ressure , microbar ; p ressure , in. Hg or

lb/in.2 (psi) (mm Hg or Pa) p a Partial pressure of dry air, in. Hg or psi (mm Hg or Pa) Pb Barometr ic pressure , in. Hg or psi (mm Hg or Pa) pr Reference sound pressure , microbar Ps Saturation vapor pressure , in. Hg or psi (mm Hg or Pa) p v Partial pressure of water vapor , in. Hg or psi (mm Hg or Pa) Q Quanti ty of flow, ft3/min (cfm) (m3/s) Qg Gas inflow, cfm (m3/s) (2„ Liquid volume flow ra te , gal/min (gpm) (m3/s or L/s) q Input of heat energy, Btu/lb (J/kg) q Rate of change in heat content , Btu/h (W) qL Rate of change in latent-heat content , Btu/h (W) qR Amount of refrigeration, tons qs Rate of change in sensible-heat content , Btu/h (W) qc Rate of heat transfer by convect ion , Btu/h (W) qe Rate of heat transfer by evapora t ion , Btu/h (W) qr Rate of heat transfer by radiation, Btu/h (W) qs Rate of heat transfer by storage, Btu/h (W) R Gas constant = 1545/molecular weight, ft lb/lb m a s s ° R (J/kg-K);

mine or airway res is tance, in .min 2 / f t 6 ( N s 2 / m 8 ) Ra Anemomete r reading, fpm (m/s) Z?eq Equivalent res is tance, in .min 2 / f t 6 ( N s 2 / m 8 ) R/, Hydraul ic radius = AIO, ft (m) Rmc Ratio of methane to total combust ible in a tmosphere (dimen-

sionless) RF Recirculation factor, % or fraction r Radius , ft (m) re Hydraul ic radius of mine opening modified for roughness , ft (m) 5 Rubbing surface area = OL, ft2 (m2) s Ent ropy , B t u / l b ° F (kJ /kg°C) ; specific gravity (dimensionless) T Absolute tempera ture , °R (K) TR Tr icket t ' s ratio (dimensionless) TLV Threshold limit value, %, ppm, mg/m3, e tc . / Tempera tu re , °F (°C) td Dry-bulb t empera ture , °F (°C) /dp Dew-point t empera ture , °F (°C) te Effective t empera ture , °F (°C) tg Globe the rmomete r reading, °F (°C) t0 Rock tempera ture at surface, °F (°C) tr Virgin-rock tempera ture , °F (°C) tw Wet-bulb tempera ture , °F (°C) tz Rock tempera ture at depth Z , °F (°C)

xvi LIST OF MATHEMATICAL SYMBOLS

U Relative velocity, ft/s (fps) (m/s) V Average velocity of flow, ft/min (fpm) (m/s) V, Critical velocity, fpm (m/s) V, Particle settling velocity, fpm (m/s) v Specific volume, ft3/lb (m3/kg) W Specific humidity, grains/lb or lb/lb (kg/kg) W Input of mechanical energy, ft lb/lb (J/kg) Wk Rate of doing work, Btu/h (W); air quantity flowing in chord k of

a network, cfm (m3/s) w Specific weight, lb/ft3 (kg/m3) X Shock-loss factor (dimensionless) x Constant of proportionality (dimensionless); concentration of con-

taminant, % or fraction; linear distance, ft (m) Y Volume, ft3 (m3) y Expansion factor (dimensionless) Z Elevation above datum, usually sea level, or potential energy, ft

(m) z Contraction factor (dimensionless)

Greek Letters

a (alpha) Thermal diffusivity, ft2/h (m2/s) 7 (gamma) Specific-heat ratio at constant pressure and volume = cp/c„

(dimensionless) e (epsilon) Thermal emissivity, Btu/hft2oF (W/m2oC); Goch-Patterson

heat-flow term (dimensionless) \ (lambda) Mean free path of gas molecules, m r\ (eta) Efficiency, % 9 (theta) Angle, degrees fji (mu) Absolute viscosity, lbs/ft2 (Pas); degree of saturation, % v (nu) Kinematic viscosity, ft2/s (m2/s) p (rho) Mass density, lbs2/ft4 (kg/m3) T (tau) Time; s, min, h, or year ()> (phi) Relative humidity, %; pseudoporosity, ratio of volume of gas

adsorbed on coal surface per atmosphere per volume of coal (dimensonless)

w (omega) Goch-Patterson heat-flow term (dimensionless); angular ve-locity, radians/s

LIST OF MAP SYMBOLS

The symbols listed here alphabetically are typical, but not standard, symbols for use on mine ventilation maps. Because standards do not exist, the reader should be careful in interpreting symbols on any given ventilation map. Variations in practice are common. First, many companies use color-coded maps to help in identifying ventilation airflows. For example, intake air can be denoted by blue arrows, return air by red arrows, escapeways by green arrows, and belt air by yellow arrows. The color scheme differs from mine to mine. Second, the style of the air directional arrows differs from mine to mine with different types of arrows used to denote intake and return airstreams.

Symbol Description

LTZZD (B)

Airflow (intake) Airflow (return) Airlock; a double-door system to allow equipment to pass through without disrupting the ventilation circuit Auxiliary fan and vent pipe or tubing (flow direction may be indicated by an arrow)

Brattice (also called a line brattice); a curtain of plastic or plastic-covered fabric hung from the roof to direct air to or from a working face Box check; a stopping with a hole in it to allow a conveyor or other equipment to pass through while limiting the airflow quantity

Check curtain; a barrier of plastic or plastic-covered fabric hung across an opening from the roof to block the flow of air Door

S

-d>-

Escapeway with direction of escape in the direction of airflow

Escapeway with the direction of escape in the direction opposite to the airflow direction

XVII

SYMBOLS

Fan (flow direction may be indicated by an arrow)

Fire door (normally open)

Main fan (the dotted lines show the location of the weak wall) Overcast or air crossing; an area where roof material is taken to allow one airflow to pass over another without mixing (the parallel lines indicate the airway that goes straight through the overcast); may also be constructed as an undercast or sidecast crossing

Overcast with a built-in regulator

Pipe overcast; a method of using pipes to pass a small quantity of return air through an intake airflow without mixing the two airflows; generally used for taking belt air directly to the return in a coal mine

Regulator

Seal

Self-contained self-rescuer cache location

Shaft with a downcast flow of air (alternately, this symbol may represent an undercast) Shaft with an upcast flow of air (note that this symbol could also represent a gas well or a borehole location on some mine maps)

Stopping (permanent); an impermeable stopping made of masonry, steel, or other flame-resistant material to block the flow of air through an opening

Stopping (temporary); a quickly erected and movable stopping normally made of brattice material to temporarily block the flow of air through an opening

Stopping with small door to allow the passage of personnel

MINE VENTILATION AND AIR CONDITIONING

PARTI

INTRODUCTION

CHAPTER 1

Environmental Control of the Mine Atmosphere

1.1 PURPOSE AND IMPORTANCE

In the vacuum of outer space, human astronauts rely on the artificial atmo-sphere of a spacecraft for their life support system. While differing in locale and mission, human miners are no less dependent on an artificial atmosphere to sustain them in underground mines where the air may be stagnant and contaminated.

It is evident that both miners and astronauts confront a hostile environ-ment, and that both groups must depend on a ventilation-air conditioning system to supply them adequate air for breathing.

Under even normal circumstances, excavation in the earth—like explora-tion in space—can be fraught with a variety of environmental problems and hazards. While ground support is an obvious and compelling need, the most vital aspect of the mine environment to control is the atmosphere of the workplace.

To the mining engineer, ventilation is the most versatile atmospheric con-trol tool. It is the process relied on to accomplish most environmental control underground. Mine ventilation is essentially the application of the principles of fluid dynamics to the flow of air in mine openings. As the primary means of quantity control, ventilation is responsible for the circulation of air, in both amount and direction, throughout the mine. It is one of the constituent processes of total mine air conditioning, the simultaneous control within prescribed limits of the quality, quantity, and temperature-humidity of mine air (Anon., 1993).

Increasingly, in underground mining, environmental objectives require that we condition air to meet quality and temperature-humidity standards as well as quantity criteria. In recent years, these standards have been raised substantially. Although threshold limits are based on human safety and toler-ance, increasing concern is being expressed for standards of human comfort as well. The provision of a comfortable work environment is both cost-effec-tive and humanitarian. Worker productivity and job satisfaction correlate closely with environmental quality. Further, excessive accident rates and workers' compensation rates are a consequence of unsatisfactory as well as

3

4 ENVIRONMENTAL CONTROL OF THE MINE ATMOSPHERE

unsafe environmental conditions. No mining company today can afford to be lax in its environmental and air-control practices.

Historical Perspectives and Natural Constraints

The importance of mine ventilation and air conditioning has not just newly been recognized. From the onset of underground mining in Paleolithic times, perhaps as early as 40,000 BCE (B.C.) (Gregory, 1980, p. 50), miners con-fronted oxygen deficiency, toxic gases, harmful dusts, and debilitating heat. As miners became more skilled, by the first millennium BCE, they learned to course the air through multiple openings or circuits to provide fresh air to the working face (Lacy and Lacy, 1992, p. 5) and to use fire-induced air currents (McPherson, 1993, p. 2).

By the Middle Ages, mine ventilation enjoyed the status of a mining art. In the most celebrated early mining treatise, Georgius Agricola (1556, p. 200), a respected German scholar and scientist, decried the evils of the foul atmospheric environments in which miners had to work and pictured their still-primitive efforts to combat these conditions:

I will now speak of ventilating machines. If a shaft is very deep and no tunnel reaches to it, or no drift from another shaft connects with it, or when a tunnel is of great length and no shaft reaches to it, then the air does not replenish itself. In such a case it weighs heavily on the miners, causing them to breathe with difficulty, and sometimes they are even suffocated, and burning lamps are also extinguished. There is, therefore, a necessity for machines which the Greeks call irvevficmKoa and the Latins, spirit ales—although they do not give forth any sound—which enable the miners to breathe easily and carry on their work.*

Figures l . l a -c , taken from Agricola's book, portray some of these early "ventilating machines." A contemporary history of mine ventilation is pre-sented by McPherson (1993, pp. 1-7).

Technology has vastly improved mine ventilation, although environmental challenges underground still abound. Depth, the most serious natural con-straint, sets the ultimate limit, specifically through rock pressure and rock temperature. Not only do rock pressures rise inexorably with depth but tem-peratures do also, with subsequent deterioration of the atmosphere. Accord-ing to Spalding (1949, p. 238):

Of all the factors which affect mining operations, high rock temperature is the one most often likely to limit the depth to which those operations can be ex-tended. The science of ventilation is therefore rapidly becoming the most im-portant branch of deep mining.

* By permission from Dover Publications, Inc.

1.2 CONTROL PROCESSES 5

At great depths, ventilation requirements and costs eventually climb to un-sustainable levels. To preserve mine atmospheric quality under these intense heat conditions, ventilation at great depths must be supplemented by air conditioning.

Although heat generated by depth imposes the ultimate limit, the mine and its atmosphere have other detrimental conditions to withstand. These consist usually of airborne contaminants such as gases and dusts. As mines expand in size, complexity, manpower, and mechanization, demands on the ventilation-air conditioning system to maintain more stringent standards of environmental quality likewise rise. Fortunately, advances in mining science and technology tend to keep pace with worsening hazards underground. The struggle, however, is a continuous one reflected in both human safety and operating costs.

1.2 CONTROL PROCESSES

Lest confusion arise in the mind of the reader, it is well to clarify some of the terms related to environmental control of the mine atmosphere. Used alone, in mining parlance, air conditioning denotes only the function of tem-perature-humidity control, generally cooling or heating. To signify total mine air conditioning and all the functions of environmental control it entails, the qualifier term "total" should be used.

To reiterate, the functions encompassed by total air conditioning are (1) quality control, (2) quantity control, and (3) temperature-humidity control of the atmosphere. To accomplish these objectives, individual conditioning processes are employed; in mining, they consist of the following:

1. Quality control (purifying air and removing contaminants) a. Gas control—vapors and gaseous matter, including radiation b. Dust control—particulate matter

2. Quantity control (regulating magnitude and direction of airflow) a. Ventilation b. Auxiliary or face ventilation c. Local exhaust

3. Temperature-humidity control (controlling latent and sensible heat) a. Cooling b. Heating c. Humidification d. Dehumidification

Control processes may be applied individually or jointly. If the objective is total air conditioning of the mine, then all three goals must be met, and multiple processes may be applied simultaneously. Several processes can serve more than one function; for example, ventilation, the most common

6 ENVIRONMENTAL CONTROL OF THE MINE ATMOSPHERE

WP m

K É L T ^ S K S T I r̂ t̂ aC

ffl&mp? ,,t| W^i^bi-^~hi, \~~AJtS' ùf J\V

fWS?35*

S^P? ST" H ? E^!&..;/

Is^i *§ ilv «»̂ ~ Wj-4^.^.

A—SILLS. B—POINTED STAKES. C—CROSS-BEAMS. D—UPRIGHT PLANKS. E—HOLLOWS. F— WINDS. G—COVERING DISC. H—SHAFTS I—MACHINE

WITHOUT A COVERINC.

(a)

A — T U N N E L . B — P I P E . C—-NOZZLE OF DOUBLE BELLOWS.

(b)

1.2 CONTROL PROCESSES 7

A-DltUM. It —HOX SHAPED CASING. C — H L O W - H O L E . I > — *>E»;o».n HHLÏ E - C O N D U I T . F — A X L E C - 1 . C V E K OK AXLF H — R O L - S .

<c) FIGURE 1.1 Mine ventilation machines of Agricola's day: (a) deflectors; (b) bel-lows; (c) fans. [Parts (a)-(c) from Agricola, 1556. By permission from Dover Publica-tions, Inc., copyright 1950.]

one in mining, performs mainly quantity control but may serve also for qual-ity control and temperature-humidity control.

In coping with atmospheric environmental hazards in mining, certain engi-neering principles are fundamental and applicable to control of any contami-nant. These contaminants consist mainly of gases and dusts but include heat and humidity as well. In order of preference of their application, engineering control principles consist of the following (Hartman, 1968):

8 ENVIRONMENTAL CONTROL OF THE MINE ATMOSPHERE

1. Prevention or avoidance 2. Removal or elimination 3. Suppression or absorption 4. Containment or isolation 5. Dilution or reduction

For example, if quality control of a dust hazard is the objective, then these five steps should be evaluated and, as appropriate, applied in the order given. Ventilation, a dilution measure, may be the ultimate solution, but it should be employed in conjunction with prevention, removal, suppression (by water), and containment (by suitable enclosure of the source).

In addition to engineering control, there are other measures at the disposal of mine officials responsible for safety, ventilation, and air conditioning. Medical control principles consist of education, physical examinations, lung x-rays, personal protective devices, prophylaxis, and therapy. Last are legal control principles, which consist of statutory and regulatory provisions and workers' compensation laws. All are resources to employ in combating envi-ronmental hazards.

Up to this point, the stated or implied reason for air conditioning or other environmental control processes is the preservation or enhancement of human life. Conditioning that controls the atmosphere that human beings breathe is termed comfort air conditioning. Nearly all mine air conditioning systems are of this type. On occasion, however, product air conditioning is employed when the objective is preservation of the plant or quality of the product. Examples are air temperature or moisture reduction to prevent slaking of coal mine roofs, absorption of water by drying to preserve deli-quescent minerals, heating of water lines in downcast shafts during winter, and dehumidification of air in wet upcast shafts.

1.3 COORDINATION OF MINING AND VENTILATION SYSTEMS

Notwithstanding its criticality to the life support process, environmental con-trol in mines poses a paradox. It does in all industry. On the one hand, environmental control is essential to the preservation of human life and nec-essary for the conduct of underground operations. On the other hand, it is ancillary to the primary objective of mining: the production of ore, rock, or coal from a mineral deposit. The paradox is that environmental control contributes nothing to production directly and yet makes the production cycle possible.

As stated previously, the two most vital environmental control measures in mining are (1) ventilation and air conditioning and (2) roof support and ground control. Ideally, they should be performed with minimum interfer-