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BUREAU OF MINES 
 INFORMATION CIRCULAR/1989 
 
 w/7 
 
 A Personal Miner's Carbon 
 Monoxide Alarm 
 
 By J. E. Chilton and C. R. Carpenter 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
Mission: Asthe Nation's principal conservation 
 agency, the Department of the Interior has respon- 
 sibility for most of our nationally-owned public 
 lands and natural and cultural resources. This 
 includes fostering wise use of our land and water 
 resources, protecting our fish and wildlife, pre- 
 serving the environmental and cultural values of 
 our national parks and historical places, and pro- 
 viding for the enjoyment of life through outdoor 
 recreation. The Department assesses our energy 
 and mineral resources and works to assure that 
 their development is in the best interests of all 
 our people. The Department also promotes the 
 goals of the Take Pride in America campaign by 
 encouraging stewardship and citizen responsibil- 
 ity for the public lands and promoting citizen par- 
 ticipation in their care. The Department also has 
 a major responsibility for American Indian reser- 
 vation communities and for people who live in 
 Island Territories under U.S. Administration. 
 
Information Circular 9233 
 
 A Personal Miner's Carbon 
 Monoxide Alarm 
 
 By J. E. Chilton and C. R. Carpenter 
 
 
 "*""»-, 
 
 
 
 
 
 : 
 
 
 . 
 
 
 
 
 
 ' 
 
 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 Manuel Lujan, Jr., Secretary 
 
 BUREAU OF MINES 
 T S Ary, Director 
 

 Library of Congress Cataloging in Publication Data: 
 
 Chilton, J. E. 
 
 A personal miner's carbon monoxide alarm / by J.E. Chilton and C.R. Carpenter. 
 
 p. cm. - (Information circular / United States Department of the Interior, 
 Bureau of Mines) 
 
 Bibliography: p. 10 
 
 Supt. of Docs, no.: I 28.27:9233. 
 
 1. Mine gases-Analysis-Equipment and supplies-Testing. 2. Carbon monoxide- 
 Analysis-Equipment and supplies-Testing. 3. Gas-detectors-Testing. I. Carpenter, 
 C. R. (Clarence R.) II. Title. III. Series: Information circular (United States. 
 Bureau of Mines) 
 
 TN295.U4 [TN305] 622 s-dc20 [622'.82] 89-600201 CIP 
 
CONTENTS 
 
 Page 
 
 Abstract 1 
 
 Introduction 2 
 
 Exposure to carbon monoxide 2 
 
 Measurement of carbon monoxide 4 
 
 Prototype carbon monoxide alarm characteristics 4 
 
 Prototype personal miner's carbon monoxide alarm 5 
 
 Test method 6 
 
 Test results 6 
 
 Humidity effects 6 
 
 Gas interferents to disk reaction 6 
 
 Temperature effects 8 
 
 Variability 9 
 
 Conclusions 10 
 
 References 10 
 
 Appendix.-Electrical schematic and component list for PEMCOAL 2 11 
 
 ILLUSTRATIONS 
 
 1. Formation of carboxy-hemoglobin by carbon monoxide exposure 3 
 
 2. Effect on health by exposure to carbon monoxide . 3 
 
 3. PEMCOAL 2 electrical function diagram 5 
 
 4. PEMCOAL 2 5 
 
 5. Apparatus for test of carbon monoxide alarm 7 
 
 6. Effect of carbon monoxide concentration and humidity on PEMCOAL alarm times 7 
 
 7. Effect of hydrogen sulfide and carbon monoxide on PEMCOAL 1 alarm times 7 
 
 8. Effect of temperature on PEMCOAL alarm times 8 
 
 9. Proposed reaction sequences for palladium chloride with carbon monoxide and water 8 
 
 10. Effect of lot number on response of CO reactive disk 9 
 
 A-l. Electrical schematic for PEMCOAL 2 12 
 
 TABLE 
 
 A-l. Electrical components for PEMCOAL 2 11 
 

 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 
 
 A 
 
 ampere 
 
 MF 
 
 microfarad 
 
 °C 
 
 degree Celsius 
 
 mg/kg 
 
 milligram per kilogram 
 
 ft 
 
 foot 
 
 min 
 
 minute 
 
 ft 3 
 
 cubic foot 
 
 mL/min 
 
 milliliter per minute 
 
 g 
 
 gram 
 
 Mohm 
 
 megohm 
 
 h 
 
 hour 
 
 pet 
 
 percent 
 
 in 
 
 inch 
 
 ppm 
 
 part per million 
 
 kohm 
 
 kilohm 
 
 ppm/min 
 
 part per million per minute 
 
 lb 
 
 pound 
 
 s 
 
 second 
 
 mA 
 
 milliampere 
 
 V 
 
 volt 
 
 mA-h 
 
 milliampere-hour 
 
 
 
A PERSONAL MINER'S CARBON MONOXIDE ALARM 
 
 By J. E. Chilton 1 and C. R. Carpenter 2 
 
 ABSTRACT 
 
 Underground miners may be exposed to hazardous quantities of toxic gases, such as carbon monoxide 
 (CO), generated from mine fires or explosions. Every underground miner is required to carry a filter 
 self-rescuer (FSR), which when operated will remove CO from the miner's breathing air. In addition, 
 every underground miner must have a self-contained self-rescuer (SCSR) near the worksite that will 
 supply breathing oxygen. In many situations, miners do not know when to don either rescuer since 
 they do not know if there is a fire in the mine, nor do they carry instrumentation necessary for the 
 detection of the toxic, colorless, and odorless fire product CO. If each miner carried a personal CO 
 alarm, which would respond to high concentrations of CO, the miner would then be alerted when to don 
 either the FSR or SCSR and exit the mine. A prototype personal miner's CO alarm called PEMCOAL 
 was developed by the U.S. Bureau of Mines. The PEMCOAL unit is small enough to be carried on 
 a miner's belt, has a flash lamp visual alarm, requires no calibration for use, and uses a chemical sensor 
 that changes color by reaction with trace quantities of CO. The chemical sensor was tested at 
 concentrations of CO from 10 to 1,000 ppm, at temperatures from 5° to 40° C, and with several potential 
 mine gas interferents. The PEMCOAL alarm times were sufficiently fast to warn miners before they 
 are exposed to hazardous quantities of CO. 
 
 Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA. 
 
INTRODUCTION 
 
 Miners could be exposed to significant quantities of CO 
 during their work experience. Coal mines may contain 
 endogenous CO, which is produced by air oxidation of 
 pyrophoric coal. Fires in mines involving coal, wood, and 
 belting materials will produce CO as one of the principle 
 components in the initial fire stage. Diesel-powered 
 engines produce CO as one constituent of the exhaust, and 
 explosive fumes from blasting also contain substantial 
 quantities of CO. 
 
 This universality of potential exposure to CO was 
 recognized by the Mine Safety and Health Administration 
 (MSHA) in promulgating rules that require every under- 
 ground miner to carry a belt-mounted self-rescuer. This 
 FSR is intended to be used in case of a mine fire or 
 explosion to remove CO from breathing air. The FSR 
 catalytically oxidizes the CO to form relatively innocuous 
 carbon dioxide (C0 2 ). Thus, by timely use of the FSR, 
 the miner can breath air purified of CO while leaving the 
 mine. This use of the FSR tacitly assumes that the con- 
 taminated air still contains sufficient oxygen for the miner 
 to breathe. Recognizing that substantial amounts of 
 oxygen may be consumed in large mine fires, and that the 
 fire may produce large quantities of toxic products so that 
 the miner cannot breath the air filtered by the FSR, 
 MSHA now requires, in addition, that all miners have a 
 SCSR stored in close proximity to their workplaces. This 
 SCSR contains either a pressurized oxygen supply or an 
 oxygen-generating chemical to provide a 1-h supply of 
 breathing oxygen for the miner to use while leaving a 
 contaminated area in the mine. 
 
 Although a miner may have an FSR and an SCSR on 
 hand, the miner will not be protected from exposure to 
 CO unless the devices are actually used. Obviously, if 
 
 miners can see the active mine fire or survive a mine 
 explosion, they will be prompted to use the breathing units 
 and leave the area. If, however, the miners are not within 
 sight of the fire, they will have to rely on receiving that 
 information from others. Usually after a fire is discovered, 
 a fire alarm is actuated and the mine supervisor is notified. 
 The supervisor will verify that there is a fire and, based 
 on the size and intensity of the fire, will have the miners 
 exit the mine or stay and fight the fire. This decision will 
 be sent to the affected miners at various work locations. 
 This may be the first time that some miners are aware 
 that there is a fire and that breathing devices should be 
 donned. The problems inherent in this complicated super- 
 visory process and the likelihood of breaking this chain of 
 logical steps was, unfortunately and tragically, illustrated by 
 the Wilberg Mine fire near Orangeville, UT, in December 
 1984, when 27 miners and management observers died 
 when some of them failed to don their SCSR's in time or 
 could not activate them to escape from the mine fire. 
 
 As a direct result of this mine accident, MSHA has 
 issued rules requiring hands-on training of underground 
 coal miners in the use of SCSR's. Through this training 
 miners will know how to quickly don their SCSR's; how- 
 ever, in addition, they will still need to know when to use 
 them. One technique of insuring the timely use of the 
 FSR's or SCSR's is to have all miners carry a personal 
 CO alarm to inform them that they are exposed to high 
 concentrations of CO and thus, prompt the miners to don 
 their breathing apparatus. This U.S. Bureau of Mines 
 report will examine the characteristics of PEMCOAL, 
 which will help the miner to know when the FSR or SCSR 
 should be used. 
 
 EXPOSURE TO CARBON MONOXIDE 
 
 The concentrations of CO to which an underground 
 coal miner is normally exposed during the work-shift 
 ranges from 2 to 4 ppm for West Virginia and Pennsyl- 
 vania mines, to 8 to 10 ppm for Illinois and western 
 Colorado mines. The sources for this CO include air 
 oxidation of coal and CO in the mine ventilation intake 
 air from surface sources. Undiluted mine diesel engine 
 exhaust CO concentrations can range from 200 ppm for 
 well maintained equipment to an MSHA limit of 2,500 
 ppm (7). 3 The ventilation air-diluted CO concentrations 
 measured in several mines range up to 20 ppm; the MSHA 
 limit for diluted diesel exhaust gas is 100 ppm CO. Coal 
 mines using explosives may typically fire 30 lb of explosives 
 per round, which generate an average of 9 ft 3 of CO (2). 
 
 3 Italic numbers in parentheses refer to items in the list of references 
 preceding the appendix at the end of this report. 
 
 If this were mixed with air in a typical heading with dimen- 
 sions of 5 by 20 by 20 ft, a concentration of 4,500 ppm CO 
 would be formed. This CO must be diluted to a safe 
 working level by fresh air ventilation before the miners 
 reenter the section to remove the loose coal. CO 
 produced by coal fires may reach concentrations of up to 
 3.0 pet (30,000 ppm) or 4.0 pet (40,000 ppm) in mines 
 sealed to extinguish the fire. 
 
 Miners may not work in air containing harmful quanti- 
 ties of noxious gases, and the concentration of any gas 
 shall not exceed the current threshold limit value (TLV) 
 for the gas (3). For CO, the TLV is an average concen- 
 tration of 50 ppm taken over an 8-h work-shift for a 40-h 
 workweek. There is also a short-term exposure limit 
 (STEL) for excursions of CO concentrations, which is 
 400 ppm CO average concentration over a 15-min period. 
 These periods should not be repeated more than four 
 times per work-shift (4). The TLV of 50 ppm CO or 
 
STEL of 400 ppm CO are concentrations to which nearly 
 all miners may be repeatedly exposed without adverse 
 health effects (5). In addition, the Occupational Safety 
 and Health Administration (OSHA) lists an immediate 
 danger to life or health (IDLH) concentration which is a 
 maximum level from which one could escape within 30 min 
 without any escape-impairing symptoms. The IDLH limit 
 for CO is 1,500 ppm (<5). 
 
 To summarize, there can be potentially lethal amounts 
 of CO generated in mines by many sources, such as fires, 
 as well as ever-present small amounts of CO to which 
 miners may be exposed without adverse effects. The 
 mission of PEMCOAL is to alert the miner only when 
 potentially harmful amounts of CO are present so that the 
 miner can take appropriate action. This action should take 
 place before the miner has been exposed to a sufficient 
 amount of CO that would prevent escape. 
 
 CO is absorbed by hemoglobin in the blood to form a 
 carboxy-hemoglobin (COHb) compound, which is more 
 stable than the oxygen-hemoglobin complex. Thus, the 
 ability of the hemoglobin in the blood to supply oxygen to 
 vital parts of the body, such as the brain and heart, is 
 impaired. The symptoms or response of humans is depen- 
 dent on the amount of COHb in the blood as shown in 
 figure 1 (7). Generally, no symptoms appear in healthy 
 humans at concentrations of COHb less than 10 pet. 
 Slight to severe headaches, impairment of judgment, dizzi- 
 ness, and shortness of breath occur between 20 to 50 pet 
 COHb, unconsciousness from 50 to 60 pet COHb, and 
 
 eventually death at 80 pet COHb. The amounts of COHb 
 are correlated to the CO exposure in ppm CO-hours 
 where at exposure of 600 ppm-hours and below there are 
 no perceptible effects (8). Obviously the exact amount of 
 COHb formed in a human at a given concentration of CO 
 for a given exposure time is dependent on (1) the breath- 
 ing rate and thus the work being performed, (2) the size 
 of the human and thus the blood volume, (3) the oxygen 
 pressure in air and thus the altitude, and (4) the ambient 
 temperature. The differences in exposure conditions and 
 in human response account for some of the data variabil- 
 ity. Another way of showing the effects of CO on adult 
 health as a function of exposure time is given in figure 2 
 (9). The MSHA limits for the TLV average concentration 
 of 50 ppm CO over a 480 min duration is well below the 
 two areas showing adverse symptoms. At the upper range 
 of 10,000 ppm CO within 3 to 5 min of exposure, a miner 
 could collapse and be in danger of death. The CO alarm 
 should operate at a level below the point where any of the 
 symptoms of headache, impairment of judgment, dizziness, 
 or nausea occur and thus, give an alarm at a level that can 
 be located on this graph below and to the left of the curves 
 showing these effects. The alarm times determined exper- 
 imentally by this work using the prototype PEMCOAL 1 
 unit from early data are shown on figure 2. With 1,000 
 ppm CO concentration, the alarm occurred in an aver- 
 age time of 8 min. Thus, the PEMCOAL unit would 
 provide an alarm before onset of the first symptoms of 
 CO poisoning. 
 
 1,000 
 
 -Headache and nausea 
 Perceptible effect 
 
 500 
 
 6 20 ° 
 O 
 
 or 
 
 CO 
 
 o 
 a. 
 x 
 
 LU 
 
 100 
 
 50 
 
 20- 
 
 -No effect 
 
 •HHn 
 
 1 ; | ■ 
 
 J I I l i i I ll 
 
 20 
 
 50 
 
 I00 
 
 BLOOD COHb, pet 
 
 Figure 1. -Formation of carboxy-hemoglobin by carbon 
 monoxide exposure. 
 
 10,000 
 
 5,000 
 
 2,000 
 
 500 
 
 200 — 
 
 100 — 
 
 20 
 
 | 1 1 — I — | I I I I I 1 I I | I i IL 
 
 Collapse, danger 
 of death 
 
 OSHA IDLH value 
 
 PEMCOAL 
 alarm points 
 
 MSHA limits'] 
 -TLV .' 
 
 J i i I i i 1 1 1 I i i I i i 1 1 1 I i i_L 
 
 12 5 10 20 50 100 200 500 1,000 
 
 TIME, min 
 Figure 2. -Effect on health by exposure to carbon monoxide. 
 
MEASUREMENT OF CARBON MONOXIDE 
 
 Several techniques are available for measuring CO in 
 the concentration range of 10 to 1,000 ppm. These include 
 (1) chemical stain tubes and disks that change color upon 
 reaction with CO, (2) electrochemical sensors that mea- 
 sure the CO oxidation current, (3) solid-state semicon- 
 ductors, such as tin oxide, which change resistance when 
 reacted with CO, and (4) infrared (IR) detectors that 
 measure light absorption by the CO. The CO stain tubes 
 and disks normally rely upon visual examination to warn 
 of high levels of CO. However, an automatic alarm is 
 preferred to relying on haphazard visual detection of 
 the CO indication. Handheld electrochemical CO moni- 
 tors with audible and visual [usually light emitting diode 
 (LED)] alarms, which are certified by MSHA for intrinsic 
 safety, are available from seven manufacturers at an aver- 
 age price of $850. In addition to the initial purchase price, 
 each monitor will have an annual maintenance cost of $250 
 to $300 for the replacement CO sensor, battery, and 
 
 gas calibration supplies. Although these electrochemical 
 monitors may now be used for this application by the more 
 affluent mining companies, the CO alarm discussed in this 
 report will be much less expensive and will not require 
 continual calibration during use. Present IR gas monitors 
 require large electrical power for operation, are not readily 
 portable, and cost $1,500 or more. Semiconductor CO 
 detectors require high electrical current for operation, and 
 are very sensitive to humidity. To date, none of the elec- 
 trochemical, IR, or semiconductor sensors have proven 
 applicable to this personal monitor concept because of 
 cost or sensitivity. New developments now occurring in 
 microsized solid-state sensors may, however, have future 
 applications for this CO alarm type. 
 
 The CO alarm discussed in this Bureau report will use 
 an optocoupler consisting of an IR LED and a photo- 
 sensitive silicon transistor to detect the change in color of 
 a chemical disk that reacts with CO. 
 
 PROTOTYPE CO ALARM CHARACTERISTICS 
 
 The PEMCOAL objective is to warn the miners of 
 exposure to potentially hazardous quantities of CO. 
 Therefore, the alarm must activate before the miner's 
 health or judgment is impaired. One goal for this alert 
 or alarm level is the OSHA IDLH standard: alarm at a 
 concentration of CO of 1,500 ppm before 30 min have 
 elapsed (6). Thus, the most critical objective can be met 
 if the alarm activates at concentrations of CO lower than 
 1,500 ppm of less than 30 min duration. The ability of the 
 disk to trigger an alarm at a given time and at a given 
 concentration of CO depends entirely upon the properties 
 of the chemical reaction of the solid compound with CO. 
 These properties include the speed of the overall reaction, 
 the arrangement of the reactive chemicals on the substrate 
 for rapid interaction of the gas phase CO with the solid 
 phase, and the ultimate reaction color change. The test 
 program, which is described below, was implemented to 
 see if this objective can be met with one type of a com- 
 mercially available palladium salt-silica gel system. 
 
 On the other hand, the alarm should not be too sensi- 
 tive, causing the miners to needlessly don their breathing 
 equipment. Tests were run at background concentrations 
 of CO, which are normally encountered in mines to verify 
 that false alarms will not be triggered. 
 
 Based on the premise that the PEMCOAL should be 
 carried by all miners, (attached to their belt or rescue 
 equipment) and that each unit should be inexpensive (cost 
 less than $50), the following criteria were used in the unit's 
 design: 
 
 S/ze-Smaller in size than a self-rescuer-5 by 3.5 by 2.5 
 in. 
 
 Weight-Less than 0.5 lb. 
 
 Calibration-Nol required if each disk is identical, con- 
 taining the same amount of the reactive chemical. This 
 requirement means that the disk manufacturer should 
 have the production system under good quality control. 
 
 Power-9-V low-current alkaline battery, available in 
 any mine locality, such as NEDA 4 1604-A. 
 
 Alarm Mode-Strobe light with pulsed operation, effec- 
 tive in dark, noisy mines. 
 
 SensingPrinciple-A chemically treated disk that changes 
 color by reaction with CO. The disk is obtained from 
 commercial, readily available sources. One type of disk 
 uses a palladium salt on a silica gel substrate, which is 
 initially a straw yellow color and reacts with CO to form 
 a gray color. 
 
 Electronic Design-Sense, the disk color change with a 
 reflective-type optocoupler containing an IR emitting 
 LED and a silicon photo detector. Minimize electrical 
 current drain by pulsing or intermittently operating 
 both the optocoupler sensor and the alarm light. 
 
 4 Reference to specific products does not imply endorsement by the 
 U.S. Bureau of Mines. 
 
PROTOTYPE PERSONAL MINER'S CO ALARM 
 
 The electronic circuitry and a CO sensing disk were 
 assembled into a plastic case suitable for wearing on a 
 miner's belt. The electrical function diagram is given in 
 figure 3 showing the relationship between the IR diode, 
 the CO sensitive disk, and the photosensitive transistor. 
 The complete electrical schematic for the most recent 
 prototype, PEMCOAL 2, is figure A-l in the appendix. In 
 this unit, a reflective optocoupler (TRW OPB 703A) is 
 positioned to view the disk during the color change caused 
 by reaction with CO. The measured voltage was 2.6 V for 
 unreacted disks, and the final voltage was 4.2 V for the 
 completely CO reacted disks (dark gray). An alarm 
 threshold voltage was chosen at 3.5 V for this application, 
 which is almost one-half of the total voltage change. The 
 703A reflective device is powered by a pulse generator 
 with periods of 0.1 s on and 1.5 s off. The voltage output 
 from the silicon phototransistor is compared with the 
 reference voltage (3.5 V), and when this voltage is exceed- 
 ed, the alarm is latched on until the next pulse sequence 
 starts. The prototype unit PEMCOAL 1 alarm is a visible 
 red LED and the PEMCOAL 2 alarm is a strobe light 
 with greater visual impact. The PEMCOAL 2 strobe light 
 and all of the high-voltage components were encapsulated 
 in a transparent flexible silicon polymer. This will render 
 flash components intrinsically safe for operation in poten- 
 tially flammable gas mixtures. The alarm is pulsed with a 
 time period of 0.05 s on and 0.5 s off, two flashes per 
 second, to conserve the battery power. The battery is a 9- 
 V transistor type with a useful capacity of 100 mA-h at 
 the 10 h rate of discharge. The average current drain is 
 3.1 mA, and it is recommended that a new battery be used 
 each week. A secondary Ni-Cd 7.2 V battery may be used 
 also with a projected service life over one year. 
 
 To check the operation of the alarm, a plastic holder 
 carrying the CO sensitive disk is inserted part of the way 
 into the unit until the closing of the spring-loaded turn-on 
 switch can be felt. The optical sensor will then view the 
 dark inner case wall. With the holder in this position, the 
 alarm lamp will flash, thus checking the operating status of 
 the electrical circuitry and the battery. The holder with 
 the disk is then pushed all of the way into the unit to posi- 
 tion the fresh unreacted disk in front of the optocoupler. 
 The alarm will then stop flashing as the sensor views a 
 fresh unreacted disk and the unit will then be ready for 
 use. The prototype unit in figure 4 shows the disk on the 
 holder before insertion into the unit. 
 
 IR-diode 
 light source 
 
 Phototransistor 
 detector 
 
 r^--i 
 
 Pulse 
 
 
 ;..Ol 
 
 generator 
 
 
 i j Reflective 
 1 i optocoupler 
 
 
 
 
 
 
 i 
 
 
 
 W 
 
 Amplifier 
 
 
 Comparator 
 
 
 Alarm 
 
 -1*! 
 
 lHj 
 
 
 
 
 
 
 
 
 
 Transparent plastic 
 encapsulation 
 
 Figure 3.-PEMCOAL 2 electrical function diagram. 
 
 Figure 4.-PEMCOAL 2. 
 
TEST METHOD 
 
 All of the following data were obtained by the PEM- 
 COAL 1 unit which was tested in the experimental setup 
 shown in figure 5. An environmental chamber was used 
 for ambient temperature control. The gas mixtures were 
 prepared using compressed cylinders of standard gases 
 diluted by air in a dynamic gas mixing system regulated 
 by mass flow controllers (10). The test gas mixture was 
 humidified using water in a gas washing bottle with a 
 fritted disk for bubble dispersion. For tests with water 
 
 soluble gas constituents, only the air diluent was humid- 
 ified. The test gas was fed into the CO alarm using a 
 plastic hood with gas flow set usually at 400 mL/min. 
 Times to alarm were measured with an electronic timer 
 containing an optical sensor that stopped the timing cycle 
 when the alarm LED was turned on. For all of this work, 
 commercially available CO sensitive chemical disks were 
 purchased from the American Gas & Chemical Co., 
 Northvale, NJ, as Leak-tec CO-50-R CO indicators. 
 
 TEST RESULTS 
 
 Initial experiments with the prototype CO alarm were 
 run at 24° C using fresh disks and immediately exposing 
 them to a CO test gas. Generally, three test gas concen- 
 trations were used: 250, 400, and 1,000 ppm CO mixtures 
 in air with 84 pet relative humidity. Alarm times mea- 
 sured with the fresh disks are shown in the lower curve in 
 
 figure 6. Average alarm times of 10.94 min were obtained 
 with standard deviation of 3.88 min for 250 ppm gas 
 challenge. At higher concentrations of CO, the disks 
 responded faster with an average alarm time of 2.58 min 
 and a standard deviation of 0.98 min for the 1,000 ppm 
 CO challenge. 
 
 HUMIDITY EFFECTS 
 
 The disks were found to have a slower response if they 
 were initially exposed to air containing water and then 
 challenged with CO, simulating their use in wet mines. 
 Tests were run for 2 h with humid air (84 pet RH), and 
 then the disks were challenged by test gases containing 
 CO. The results of these tests are plotted on the upper 
 curve in figure 6. The alarm times at 250 ppm CO were 
 an average of 49.5 min with a standard deviation of 12.03 
 min. At 1,000 ppm CO gas challenge, the alarm times 
 were an average of 8.4 min or over 3 times as long as the 
 alarm times obtained with the fresh disks. 
 
 Several tests were run with the initial CO test con- 
 centration at 10 ppm CO in humid air for 6-h duration, 
 simulating typical mine background levels of CO. The 
 
 PEMCOAL unit did not alarm at the 10 ppm CO concen- 
 tration level during the 6-h exposure. At the end of each 
 test, the unit was then challenged with a higher concen- 
 tration of CO. Alarm times of 12 and 16 min were mea- 
 sured at 1,000 ppm CO, alarm times of 30 and 36 min at 
 400 ppm CO, and alarm times of 78 min at 250 ppm CO 
 challenge gas. This test simulated the use of the CO 
 alarm by coal miners working in a mine with high humidity 
 (84 pet RH) with a background concentration of CO of 
 10 ppm, and having a fire occur after they had been work- 
 ing for 6 h. The units would still respond before the 
 miner was adversely affected by the ambient CO at con- 
 centration levels from 250 to 1,000 ppm CO. 
 
 GAS INTERFERENTS TO DISK REACTION 
 
 Several gas interferents to the reaction of CO with 
 the chemical disks were examined. The interferent gases 
 included hydrogen sulfide (H 2 S) formed in mines by 
 reaction of sulfide minerals with acid mine water, sulfur 
 dioxide (S0 2 ) generated in mine fires from burning of 
 sulfur-containing materials and present in diesel engine 
 exhaust from sulfur in the fuel, and nitric oxide (NO) and 
 nitrogen dioxide (N0 2 ) both formed in diesel engine 
 exhaust and in gas fumes from explosive blasting. 
 
 The PEMCOAL 1 unit was run in air with 50 ppm S0 2 
 for 3 h; no alarm was obtained. This exposed disk was 
 then challenged with 1,000 ppm CO and an alarm time of 
 7 min was measured. This alarm time for the 1,000 ppm 
 
 CO measured after the 3-h exposure to SO z was equivalent 
 to the average alarm time of 8 min previously found in 
 runs at 1,000 ppm CO after a 2 h exposure to moist air. 
 With additional tests at 25 ppm S0 2 and 243 ppm CO, 
 alarm time of 18 min was measured. With 5 ppm S0 2 and 
 255 ppm CO, alarm times of 7 min and 6.3 min were 
 measured. With tests at 255 ppm CO alone, alarm times 
 of 9.5 and 8.7 min were obtained. Thus, at a concentra- 
 tion of 5 ppm S0 2 there is very little effect on the CO disk 
 reaction. The TLV for S0 2 is 2 ppm, and if the mine is 
 operating under compliance for allowable toxic gases (3), 
 no effect of S0 2 is expected on the CO alarm. 
 
CO 
 
 
 
 
 Gas 
 
 mixing 
 system 
 
 
 
 A 
 
 
 
 Air 
 
 
 Plastic cap 
 
 Humidifier 
 
 Temperature-controlled 
 environmental chamber 
 
 Figure 5.-Apparatus for test of carbon monoxide alarm. 
 
 IUU 
 
 - 
 
 1 
 
 1 
 
 1 1 
 
 - 
 
 
 _ 
 
 \ ° 
 
 
 
 
 
 50 
 
 — 
 
 V 
 
 
 
 — 
 
 
 - 
 
 o 
 
 o 
 \ ° 
 
 
 - 
 
 
 
 
 o 
 
 / Expose 2h, 
 / 84pctRH 
 C air before test 
 
 " 
 
 20 
 
 — 
 
 
 
 
 — 
 
 c 
 
 
 X 
 
 
 
 
 ALARM TIME, m 
 
 o 
 
 - 
 
 \ : 
 
 X 
 
 X \ 
 
 X ^ 
 X 
 
 \ X 
 
 \ X 
 
 ^~- Immediate test 
 
 ~o 
 
 5 
 
 
 
 X 
 
 
 — 
 
 
 
 
 X 
 
 
 
 
 
 
 
 
 X 
 
 2 
 1 
 
 
 1 
 
 1 
 
 1 1 
 
 X 
 
 H 
 
 1! 
 
 200 400 600 
 
 CO CONC, ppm 
 
 800 1,000 
 
 The PEMCOAL 1 unit was run in 7 ppm NO for 3 h 
 and no alarm was obtained. This unit was then challenged 
 with 7 ppm NO and 250 ppm CO, and an alarm time of 
 10.5 min was obtained. When a fresh disk was run in a 
 mixture of 7 ppm NO and 242 ppm CO, an alarm time of 
 6.2 min was measured. For comparison, a run in 241 ppm 
 CO alone had an alarm time of 8.7 min. Thus, the pres- 
 ence of NO did not significantly effect the response of the 
 CO chemical disk. The TLV for NO is 25 ppm and typical 
 concentrations measured in several coal mines with diesel- 
 powered equipment are less than 8 ppm NO. 
 
 The PEMCOAL 1 unit was run in 8.9 ppm N0 2 with 
 254 ppm CO, and an alarm time of 90 min was measured. 
 With 3.6 ppm N0 2 in 248 ppm CO, an alarm time of 29.7 
 min was measured. The alarm time for the unit exposed 
 to 276 ppm CO alone was 7 min. Thus, N0 2 in these tests 
 is an interferent to the reaction of the CO chemical disk. 
 The PEMCOAL 2 unit has a dust filter composed of open 
 cell porous polyurethane placed over the gas inlet ports. 
 This unit had alarm times of 2.9 and 5.7 min when tested 
 in 3.6 ppm N0 2 with 248 ppm CO, and when tested with 
 3.6 ppm N0 2 with 908 ppm CO had an alarm time of 2.3 
 min. Thus, no effect was found on the PEMCOAL 2 unit 
 from the N0 2 . In these tests, the foamed plastic filter 
 adequately removed the N0 2 from the CO mixture. The 
 TLV for N0 2 is 3 ppm and measurements in mines with 
 diesel-powered equipment have found concentrations of 
 1 ppm or less. 
 
 Tests of the PEMCOAL 1 unit with H 2 S showed a 
 strong positive interference to the CO chemical reaction 
 (fig. 7), which shows the alarm times obtained at various 
 gas concentrations. CO reacts with the sensor disk to 
 
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 10 100 
 
 ALARM TIME, min 
 
 1,000 
 
 Figure 6.-Effect of CO concentration and humidity on the 
 PEMCOAL alarm time. 
 
 Figure 7.-Effect of hydrogen sulfide and carbon monoxide on 
 PEMCOAL 1 alarm times. 
 
H 2 S reacts with the sensor 
 
 form gray palladium metal 
 
 disk to form black colored palladium sulfide 
 
 more sensitive to H 2 S by a factor of 2 over the CO. If a 
 
 mine atmosphere contained H 2 S, a chemical filter contain- 
 ing zinc, lead, or mercury salts would be added to the unit 
 to remove the interferent. The TLV for H 2 S is 10 ppm 
 and at this concentration an alarm time of 55 min would 
 be obtained with the CO reactive disk. 
 
 To summarize the effect of gaseous interferents on 
 
 The disk is the CO disk reaction, significant quantities of N0 2 would 
 
 increase the alarm times and H 2 S would shorten the alarm 
 
 times for the CO detection, while both S0 2 and NO would 
 give minimal effects at the low concentrations expected 
 in mines. 
 
 TEMPERATURE EFFECTS 
 
 The effect of ambient temperature on the alarm times 
 was measured from 5° to 40° C as presented in figure 8. 
 
 100 
 
 10 20 30 
 
 TEMPERATURE, °C 
 
 Figure 8. -Effect of temperature on PEMCOAL alarm times. 
 
 The alarm times were quicker at the higher temperatures 
 for all three gas concentrations. At 5° C and with 250 ppm 
 CO challenge gas, several of the tests did not alarm in 100 
 min. When the disks were removed from the test fixture, 
 the disks were still the original light straw yellow color, but 
 turned dark gray as the disks were, warmed in air. This 
 observation leads to the conclusion that the disks adsorb 
 the CO at the low temperature, but the subsequent reac- 
 tion of the adsorbed CO with palladium ion to produce the 
 metallic palladium is slow at low temperatures. 
 
 The slow reaction of CO with palladium salts at low 
 temperature, and the slow reaction in the presence of 
 excess water may be explained by the hypothesized reac- 
 tion sequences presented in figure 9. The interaction of a 
 palladium chloride coordinated complex with water and 
 CO is indicated. The equilibrium constant for the forma- 
 tion of the palladium-water complex is probably greater 
 than the equilibrium constant for the palladium CO-water 
 
 H 
 
 I 
 H — 0. CI. CI 
 
 ^Pd Pd 
 
 CI *CI * — H 
 
 I 
 
 H 
 
 I + 2H0H z^: 2 
 
 Initial 
 
 palladium 
 I 
 
 salt 
 
 (straw yellow) 
 
 
 H 
 
 1 
 
 
 
 1 
 H-0 
 
 CI' 
 
 Pd 
 
 -H 
 
 1 + 2 CO 
 
 n 
 
 CO. CI 
 
 •pdf 
 
 Cl^ *0 — H 
 
 IE 
 
 H 
 
 hi 
 
 Pd°+ C0 2 + 2 HCI 
 
 (gray- 
 black ) 
 
 Figure 9. -Proposed reaction sequences for palladium chloride 
 with carbon monoxide and water. 
 
mixed complex because of the loss of reactivity of the 
 palladium complex in the presence of excess water. By 
 storing unreacted disks over concentrated sulfuric acid the 
 water was removed from the disks and the disks changed 
 
 color from the pale straw yellow color to a darker orange 
 color. The dried disks did not react with dry 1,000 ppm 
 CO during tests for an hour. Thus, some water is neces- 
 sary for the reaction of the palladium compound with CO. 
 
 VARIABILITY 
 
 The CO reactive disks were purchased in lots contain- 
 ing 10 plastic sealed disks. To determine the alarm time 
 variance for the disks within a lot and the alarm time 
 variance from lot to lot, data were collected from tests of 
 disks with 250 and 1,000 ppm CO exposure. A plot of the 
 disk lot numbers versus the products of the CO test con- 
 centration with the measured alarm time is given in fig- 
 ure 10. If the reaction rate for the formation of palladium 
 metal is a function of the CO concentration, the amount 
 of palladium formed is proportional to the product of the 
 CO concentration and the alarm time. If the palladium 
 metal is uniformly spread over the disk, a given amount of 
 palladium will form a fixed optical density change on the 
 disk. Since the disk color density for alarm is a constant 
 determined by the optocoupler characteristics and by 
 the alarm set voltage, the products of the gas concen- 
 tration and the alarm time should be a constant. The 
 average value for the products measured at 250 ppm CO 
 is 2,087 ppm min with a standard deviation of 540 ppm 
 min or a relative standard deviation of 25.9 pet. The 
 average value for the products measured with 1,000 ppm 
 CO is 2,278 ppm min with a standard deviation of 498 ppm 
 min or a relative standard deviation of 21.9 pet. These lot- 
 to-lot relative standard deviations (coefficient of variances) 
 are of the same magnitude as the within-lot relative stan- 
 dard deviations for lot 27 of 22.6 and 15.5 pet. An analysis 
 of variance test was run on the data from the different lots, 
 and there was no significant difference between the lot-to- 
 lot variances and the within-lot variances. The product 
 values for lot 27 seem to fall below the lot average values 
 indicating that these disks may be more sensitive to CO; 
 however, the values are within the three sigma range for 
 normal scatter of data. 
 
 The range of data in figure 10 shows that at 1,000 ppm 
 CO exposure the alarm times varied from 1.6 to 3.2 min. 
 Some of the disk alarm time variation may be due to 
 different amounts of palladium material on the disks. 
 Chemical analysis for palladium by inductively coupled 
 plasma emission was performed on extracts from four 
 
 disks, two from lot 17 with high sensitivity and two from 
 lot 22 with lower sensitivity (longer alarm times). The 
 weight of palladium plus silica material on each disk is 
 approximately 0.1 g. For lot 17, the average amount of 
 palladium was 1,530 mg/kg of material with a standard 
 deviation of 99 mg/kg and for lot 22 the average was 
 1,385 mg/kg of material with a standard deviation of 
 21 mg/kg. Since the difference between these analyses 
 are not statistically significant, other factors than total 
 palladium content may affect the disk response times, 
 such as the type and amount of silica gel binder and the 
 uniformity of the metal deposits on the disk surface. 
 Good quality control measures must be taken by the 
 manufacturer to assure a consistent and uniform response 
 to CO for each of the disks. 
 
 35 
 
 30 
 
 f 25 
 
 E 
 
 Q. 
 
 ^ 20 
 
 o 
 
 Q 
 O 
 
 cr 
 
 Q- 
 
 15 
 
 o o oo 
 .. o 
 
 x o 
 
 o 
 
 KEY 
 x 1 ,000 ppm CO 
 o 250 ppm CO 
 
 10 15 20 
 
 LOT NUMBER 
 
 25 
 
 30 
 
 disk. 
 
 Figure 10.-Effect of lot number on response of CO reactive 
 
10 
 
 CONCLUSIONS 
 
 A prototype personal miner's CO alarm has been de- 
 signed and fabricated using a commercial solid chemical 
 disk, which changes color in the presence of CO. This 
 prototype alarm is designed to warn a miner of exposure 
 to potentially harmful amounts of CO before the miner 
 can experience adverse health effects. Operation of two 
 models, PEMCOAL 1 and 2, have been tested at CO 
 concentrations to 1,000 ppm where the alarm times range 
 from 2 to 3 min for tests at room temperature. The cost 
 of parts purchased singly for the unit are under $40, and 
 if the primary transistor battery and the disk were changed 
 each week, the unit would incur an additional maintenance 
 charge of $1.75 weekly. In the event of a mine disaster 
 generating a large amount of CO, the use of this unit to 
 warn a miner to don protective breathing equipment and 
 exit the mine would substantially improve the miner's 
 chance of survival. 
 
 Successful operation of the CO alarm in mines depends 
 critically upon a reliable source of reproducible disks. 
 Thus, it is necessary to obtain data on the disk quality 
 control, or alternately, to find a separate source of high- 
 quality CO reactive disks. The present CO alarm uses a 
 palladium salt to react with the CO. The chemistry of 
 other potentially CO reactive compounds should be exam- 
 ined to find alternate color-changing reactions which may 
 be more sensitive and more reversible. Gaseous inter- 
 ferents to the operation of the CO reactive disks such as 
 H 2 S were verified and techniques can be devised to remove 
 these interferences for in-mine use. Ultimately, in-mine 
 tests need to be conducted for testing of durability and for 
 identifying potential problems caused by operation in the 
 presence of water aerosol and coal dust. 
 
 REFERENCES 
 
 1. U.S. Code of Federal Regulations. Title 30-Mineral Resources; 
 Chapter I-Mine Safety and Health Administration, Department of 
 Labor; Subchapter E-Mechanical Equipment for Mines; Part 32 Mobile 
 Diesel-Powered Equipment, sec. 32.4 (f) (1); July 1, 1987, p. 204 
 
 2. Garcia, M. M., E. P. Jucevic, and W. C. Kjttrell. Monitoring of 
 Gases From Explosives Detonated in an Underground Mine (contract 
 HO395098, Univ. AZ). BuMines OFR 72-83, June 1982, 81 pp.; NTIS 
 PB 83-191718. 
 
 3. U.S. Code of Federal Regulations. Title 30-Mineral Resources; 
 Chapter I-Mine Safety and Health Administration, Department of 
 Labor. Subchapter O-Coal Mine Health and Safety-Part 56-Subpart 
 Coal Mine Safety and Health, Part 75 Manditory Safety Standards- 
 Underground Coal Mines, Subpart D, sec. 75.301-2, July 1, 1985, p. 444. 
 
 4. American Conference of Governmental Industrial Hygienists 
 (Cincinnati, OH). Threshold Limit Values and Biological Exposure 
 Indices for 1988-1989. 1988, 116 pp. 
 
 5. American Conference of Governmental Industrial Hygienists 
 (Cincinnati, OH). Documentation of the Threshold Limit Values for 
 Substances in Work Room Air. 1971, pp. 41-43. 
 
 6. National Institute for Occupational Safety and Health. NIOSH 
 Pocket Guide to Chemical Hazards. DHEW publ. 78-210, Sept. 1985, 
 p. 72. 
 
 7. Sax, N. I. Dangerous Properties of Industrial Materials. Van 
 Nostrand Reinhold, 4th ed., 1975, p. 520. 
 
 8. National Institute for Occupational Safety and Health (Cincinnati, 
 OH). Criteria for a Recommended Standard Occupational Exposure 
 to Carbon Monoxide. 1972, 110 pp. 
 
 9. Slusher, G. R. An Evaluation of Low Cost Carbon Monoxide 
 Indicators. FAA Tech. Rep. ADS-80, 1966, p. 14. 
 
 10. Carpenter, C. R., J. E. Chilton, and G. H. Schnakenberg, Jr. A 
 Dynamic Gas-Mixing System. BuMines IC 8934, 1983, 30 pp. 
 
11 
 
 APPENDIX.-ELECTRICAL SCHEMATIC AND COMPONENT LIST FOR PEMCOAL 2 
 
 Table A-l is a listing of the electrical components and figure A-l is the electrical schematic for the PEMCOAL 2. 
 
 B 
 
 CI, C2 
 
 C3 
 
 C4, C5 
 
 Dl, D2, D3 
 
 D4 
 
 D5 
 
 F 
 
 J 
 
 N 
 
 Rl 
 
 R2 
 
 R3 
 
 R4 
 
 R5 
 
 R6 
 
 R7 
 
 R8, R9 
 
 RIO 
 
 Rll 
 
 R12 
 
 R13 
 
 R14, R15 
 
 R16 
 
 R17 
 
 R18 
 
 R19 
 
 R20 
 
 R21 
 
 R22 
 
 R23 
 
 R24 
 
 S 
 
 Tl 
 
 T2 
 
 T3, T4 
 
 T5 
 
 Ul, U2 
 
 Z 
 
 'See figure A-l. 
 
 2 Kit C 35655, Edmond Scientific. 
 
 Battery, 
 
 9-V, NEDA 1604 A. 
 
 Capacitor, 1-^F. 
 
 Capacitor, 4-/zF. 
 
 Capacitor, 0.01-/iF. 
 
 Diode, 1N645. 
 
 Diode, 1N4002. 
 
 Diode, 1N4007. 
 
 Flash tube. 2 
 
 Optocoupler, OPB 702A (TRW). 
 
 Neon bulb, NE. 
 
 Resistor 
 
 10-kohm. 
 
 Resistor 
 
 2.2-kohm. 
 
 Resistor 
 
 270-kohm. 
 
 Resistor 
 
 10-kohm. 
 
 Resistor 
 
 1-kohm. 
 
 Resistor 
 
 390-kohm. 
 
 Resistor 
 
 30-kohm. 
 
 Resistor 
 
 4.7-kohm. 
 
 Resistor 
 
 2.2-kohm. 
 
 Resistor 
 
 1-Mohm. 
 
 Resistor 
 
 1-kohm. 
 
 Resistor 
 
 100-kohm. 
 
 Resistor 
 
 1-kohm. 
 
 Resistor 
 
 100-kohm. 
 
 Resistor 
 
 1.47-kohm. 
 
 Resistor 
 
 15-kohm. 
 
 Resistor 
 
 10.5-kohm. 
 
 Resistor 
 
 22- to 47-ohm, adjustable. 
 
 Resistor 
 
 3-kohm. 
 
 Resistor 
 
 100-kohm. 
 
 Resistor 
 
 3.9-Mohm. 
 
 Resistor 
 
 1-Mohm. 
 
 Switch, ] 
 
 L-SM-1. 
 
 Transisti 
 
 K. 2N2222. 
 
 Transisti 
 
 3r. 2N2707. 
 
 Transistor. 2N2222. 
 
 Transistor, SCR, 24 NEC. 
 
 Transformer. 2 
 
 Transparent silicone elastomer, Sylgard 182 (Dow Corning). 
 
12 
 
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 Figure A-1. -Electrical schematic for PEMCOAL 2. See table A-1 for a description of components. 
 
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