Professor Arthur T. Johnson
Journal of the International Society for Respiratory Protection, 2013, vol 30(2): 1-12.
Prakash Chapain
Omar Bekdash
Arthur T. Johnson
ABSTRACT
Even though closed-circuit self-contained breathing apparatus (CC-SCBA) used in firefighting and other combustible atmospheres can possibly improve physical performance of the wearer and have increased service times by recycling the exhaled air, there exists a serious burn hazard to the wearer due to oxygen-enriched air leaking from the positive-pressure facepiece area of the CC-SCBA. NIOSH has imposed a long-standing advisement against the use of oxygen-based closed-circuit respirators in high radiant or open flame environments. The purpose of this study was to develop and employ a flow sensing system to be installed on a SCBA unit with a goal of minimum oxygen leak detection and quantification. Three flow sensors were placed and adapted at various locations of the oxygen flow loop, and the flow data, taken on a breathing machine and headform, were acquired to determine the magnitude of the various leaks induced on the facepiece area. Five different leak sizes were induced during normal breathing by installing different diameter tubes on the periphery of the face piece of the CC-SCBA allowing for air to escape at different rates that increased with increasing diameter of the tubes. Flow measurements were performed for seven different conditions: no leak, no leak repeated, and 5 different leak sizes. For each sensing unit, total flow and mean flow rates were calculated and the information was used to determine the magnitude of total leaks. Results indicated two major conclusions: i) Mean flow rates of inhalation and exhalation decreased with increasing leak sizes, ii) Calculated leaks increased with increasing induced leaks. Both of these analytical observations validated the theoretical assumption under which the experiments were performed. A less than 5 % difference was observed between two no leak conditions; and between no leak and the smallest leak conditions, a more than 20 % difference was observed indicating a sufficient sensitivity of the system necessary to differentiate a leak from a no leak scenario. There was a greater than 350 % difference calculated between the biggest induced leak and no leak condition. Results were limited by the reproducibility of the breathing waveform. However, given that restriction, the obtained positively indicate that a flow based sensor system for oxygen leak detection can be employed for developing safer CC-SCBA units to be used in combustible environments.
Journal of the International Society for Respiratory Protection, 2013, vol 30(1): 53-61.
Omar Bekdash
Prakash Chapain
Arthur T. Johnson
Abstract
The goal of this work was to develop and validate an oxygen leak detection system for use with a closed circuit self-contained breathing apparatus (CC-SCBA). CC-SCBAs operate under a positive pressure closed loop, where carbon dioxide is removed from exhaled air while oxygen and other gases are recovered and recycled. There has been a long standing NIOSH prohibition against the use of such oxygen based closed circuit systems in the presence of high radiant heat or open flame due to concerns over possible user burn injury as a result of leaks in the vicinity of the facepiece. Past studies performed according to the NFPA 1981 standard have revealed that facepiece fit poses the biggest risk for a closed circuit respirator and will most likely be the location for a leak to occur. The system developed here was intended to detect leaks emanating from the facepiece seal using a plenum with sampling ports at intervals located along the periphery of the facepiece to pull air to an oxygen analyzer. Leaks were located at the neck, temple, and cheek of the facepiece and the changes in percent oxygen in the surrounding air were recorded for leak and no leak conditions. With this approach the oxygen leaks can be sensed directly and independently of size or location. It was found that the proposed system is capable of sampling from the vicinity of the facepiece; however its sensitivity in detecting leaks was not found to be adequate enough to definitively state if a leak had occurred due to large fluctuations in oxygen detected as a result of a low sample rate and a high dilution factor.
J. ISRP 29(1): 1-12 (2012)
Frank C. Koh
Arthur Johnson
ABSTRACT
Respiratory protection plays an important role in maintenance of wearer health and safety. Previous research has shown that the two loose-fitting PAPRs tested here have very low protection factors. These respirators do not offer the protection that they are supposed to, and the question is why they do not. This investigation was undertaken to determine if these low values could be explained by the flow pathways taken by contaminated air from the leakage points to the mouth. Two loose-fitting powered air-purifying respirators were challenged with a glycerol fog to determine flow pathways and amounts within the facepieces. Fog was drawn from the environment around the respirator by either a steady vacuum (to determine flow pathways) or a breathing machine (to determine inhaled amounts). Movement of the fog within the facepiece was captured by digital video and examined frame-by-frame. It was found that the loose-fitting PAPR without a scarf offered no protection against the fog (protection factor = 1), whereas the PAPR with a scarf allowed up to 1.4L of inhaled breath before the fog reached the mouth (protection factor > 1). Tilting the head affected the amount of protection given by the PAPR. It was concluded that the presence of the blower was no guarantee of protection and that this PAPR should be worn only in a situation not dangerous to life or health.
J. ISRP 28(1): 40-47 (2011)
Elizabeth Brokaw
Arthur Johnson
Richard McCuen
ABSTRACT
Starting with minute volume data and equations previously appearing in the paper by Caretti and Coyne (2006), a power transformation was made to improve the linearity of the fit. The resulting transformed data improved the agreement between measured and predicted values of minute volumes. The equation is:
VE = (0.00366 W - 0.392 Rin + 0.173 m - 7.586)1.382
where W is specific work rate in Watts/m2, Rin is inhalation resistance in cm H20•sec/L, and m is body mass in kg. Using this equation, values of minute volumes may be predicted for 95% of the population of data points by multiplying by 1.5. Peak flows can also be calculated based upon these minute volumes. These data could be useful for respirator mask design and testing.
Journal of Environmental and Public Health, 2011, Article ID 402148.
Arthur T. Johnson
Frank C. Koh
William H. Scott Jr.
Timothy E. Rehak
ABSTRACT
This experiment was conducted to determine how much contaminant could be expected to be inhaled when overbreathing several different types of respirators. These included several tight-fitting and loose-fitting powered air-purifying respirators (PAPRs) and one air-purifying respirator (APR). CO2 was used as a tracer gas in the ambient air, and several loose-and tight-fitting respirators were tested on the head form of a breathing machine. CO2 concentration in the exhaled breath was monitored as well as CO2 concentration in the ambient air. This concentration ratio was able to give a measurement of protection factor, not for the respirator necessarily, but for the wearer. Flow rates in the filter/blower inlet and breathing machine outlet were also monitored, so blower effectiveness (defined as the blower contribution to inhaled air) could also be determined. Wearer protection factors were found to range from 1.1 for the Racal AirMate loose-fitting PAPR to infinity for the 3M Hood, 3M Breath-Easy PAPR, and SE 400 breath-responsive PAPR. Inhaled contaminant volumes depended on tidal volume but ranged from 2.02 L to 0 L for the same respirators, respectively. Blower effectiveness was about 1.0 for tight-fitting APRs, 0.18 for the Racal, and greater than 1.0 for two of the loose-fitting PAPRs. With blower effectiveness greater than 1.0, some blower flow during the exhalation phase contributes to the subsequent inhalation. Results from this experiment point to different ways to measure respirator efficacy.
Journal of Environmental and Public Health, 2011, Article ID 473143.
Frank C. Koh
Arthur T. Johnson
Timothy E. Rehak
ABSTRACT
A combination of local flow measurement techniques and fog flow visualization was used to determine the inward leakage for two tight-fitting powered air-purifying respirators (PAPRs), the 3M Breathe-Easy PAPR and the SE 400 breathing demand PAPR. The PAPRs were mounted on a breathing machine head form, and flows were measured from the blower and into the breathing machine. Both respirators leaked a little at the beginning of inhalation, probably through their exhalation valves. In both cases, the leakage was not enough for fog to appear at the mouth of the head form.
Improved Prediction of Minute Volume Flow Rates
Journal of the International Society for Respiratory Protection 2011 28(1) 2011:40-47.
Elizabeth Brokaw
Arthur Johnson
Richard McCuen
ABSTRACT
The ability to predict respiratory minute volumes while wearing respirators can be important to the design, specification, testing, and use of respirators. Starting with minute volume data and equations previously appearing in the paper by Caretti and Coyne (2006), a power transformation was made to improve the linearity of the fit. The resulting transformed data improved the agreement between measured and predicted values of minute volumes. The equation is:
VE = (0.00366 W - 0.392 Rin + 0.173 m - 7.586)1.382
where VE is minute volume in L/min, W is specific work rate in Watts/m2, Rin is inhalation resistance in cm H20•sec/L, and m is body mass in kg. Using this equation, values of minute volumes may be predicted for 95% of the population of data points by multiplying by 1.5. Peak flows can also be calculated based upon these minute volumes.
J Occup Environ Hyg. 2008 May;5(5):325-9.
A.T. Johnson
F.C. Koh
S. Jamshidi
T.E. Rehak
ABSTRACT
Leakage from loose-fitting PAPRs (powered air-purifying respirators) can compromise the safety of wearers. The Martindale Centurion MAX multifunction PAPR is a loose-fitting PAPR that also incorporates head, eye, and ear protection. This respirator is used in mines where coal dust usually is controlled by ventilation systems. Should the respirator be depended on for significant respiratory protection? Ten human volunteers were asked to wear the Centurion MAX inside a fog-filled chamber. Their inhalation flow rates were measured with small pitot-tube flowmeters held inside their mouths. They were video imaged while they breathed deeply, and the points at which the fog reached their mouths were determined. Results showed that an average of 1.1 L could be inhaled before contaminated air reached the mouth. As long as the blower purges contamination from inside the face piece during exhalation, the 1.1 L acts as a buffer against contaminants leaked due to overbreathing of blower flow rate.
Keywords: dead volume, protection, protection factor, respiration
J Occup Environ Hyg. 2007 Jan;4(1):49-53.
A.T. Johnson AT
W.H. Scott
F.C. Koh
S.J. Phelps
E.B. Francis
E. Lopresti
ABSTRACT
Self-contained self rescuers (SCSRs) are used for emergency escapes in oxygen-deficit atmospheres. Certified by NIOSH to last 1 hour, SCSRs generate oxygen by chemical reaction and must meet a minimum oxygen generation time of 60 min when used according to instructions. Wearers must walk or crawl at a controlled rate to conform to the limits of the devices. The aim of the is study was intended to determine the distance that can be walked when using SCSRs as intended. Fourteen volunteer subjects walked on a treadmill at moderate rates that they controlled. They were instructed to walk as far as possible without using oxygen at a rate higher than the SCSR could produce. Distances walked ranged from 2.1 km to 9.2 km with an average distance of 6.0 km. SCSR operating times ranged from 30 min to 94 min. If the required walking distance is farther than this, multiple units will have to be available to allow safe escape.
Keywords: emergency response, miners, oxygen supply.
J Occup Environ Hyg. 2006 Sep; 3(9):490-500.
K. Coyne
D. Caretti
W. Scott
A. Johnson
F. Koh
ABSTRACT
There has been a long-standing debate regarding the adequacy of airflow rates used in respirator certification testing and whether these test flow rates underestimate actual values. This study investigated breath by breath inspiratory peak flow rate, minute ventilation, and instantaneous flow rates of eight young, healthy volunteers walking on a treadmill at 80-85% of maximal aerobic capacity until exhaustion while wearing an air-purifying respirator with one of eight combinations of inhalation and exhalation resistance. An analysis of variance was performed to identify differences among the eight conditions. Scheffe's post hoc analysis indicated which means differed. The group of conditions with the highest average value for each parameter was identified and considered to represent a worst-case scenario. Data was reported for these conditions. A Gaussian distribution was fit to the data and the 99.9% probability levels determined. The 99.9% probability level for the peak and instantaneous flow rates were 374 L/min and 336 L/min, respectively. The minute ventilation distribution was not Gaussian. Less than 1% of the recorded minute ventilations exceeded 135 L/min. Instantaneous flow rates exceeded the National Institute for Occupational Safety and Health's respirator test standards of 64, 85, and 100 L/min constant flow 91%, 87%, and 82% of the time, respectively. The recorded minute ventilations exceeded the 40 L/min minute ventilation test standard (for tests with a sinusoidal flow pattern) 100% of the time. This study showed that young, healthy respirator wearers generated peak flow rates, minute ventilations, and instantaneous flow rates that consistently exceeded current test standards. Their flow rates should be higher than those of a respirator wearer performing occupational work and could be considered upper limits. Testing respirators and respirator cartridges using a sinusoidal breathing pattern with a minute ventilation of 135 L/min (peak flow rate approximately 424 L/min) would encompass 99% of the recorded minute ventilations and 99.9% of the predicted peak and instantaneous flow rates from this study and would more accurately reflect human respiration during strenuous exercise.
Keywords: respirators, physiology, protection, comfort, frequency components.
Journal of the International Society for Respiratory Protection, Vol. 23 (2006)
Arthur T. Johnson
ABSTRACT
Peak flow rates developed during inhalation may have little effect on filter testing, but may still directly affect protection by influencing whether or not an uncomfortable respirator is worn when it should be. Subjective comfort may have a physiological basis related to the rate of respiratory work, flow wave shape, developed muscle pressures, and others. Peak inhalation flow rate contributes to each of these. For this reason, peak inhalation flow rates cannot be easily dismissed. Needs of human wearers are important factors contributing to protection.
Keywords: Respirators, Physiology, Protection, Comfort, Frequency components.
Journal of the International Society for Respiratory Protection, Vol. 23 (2006)
Arthur T. Johnson
William H. Scott
Frank C. Koh
Erica B. Francis
Erika R. Lopresti
Stephanie J. Phelps
ABSTRACT
Powered Air Purifying Respirators (PAPR) sometimes locate weights of blower, batteries, and filter on the head. When recommending that more powerful equipment be used, the result is usually more mass carried on the head. To date, none have determined the performance time penalty caused by extra mass even though there are many reports to determine the metabolic effects of added weight on the head. This study was performed to evaluate possible work performance time using several helmet weights at 80-85% VO2 max. Nine subjects were tested with four weighted helmets of 0.54, 1.03, 1.85, and 3.36 kg. This study showed that performance time in minutes was linearly related to helmet mass: tperf = 20.25 – 2.552*kg. Each additional kilogram of mass resulted in 2.5 minutes less time. The comfort of the helmet also decreased as mass increased
Keywords: Respirator mask, ergonomics, Work capacity, load.
Journal of Occupational and Environmental Hygiene, 3: 214-224
David M. Caretti
Karen Coyne
Arthur Johnson
William Scott
Frank Koh
ABSTRACT
Respiratory inspiratory and expiratory breathing resistances impact ventilation and performance when studied independently. However, it is less clear as to how various combinations of inhalation and exhalation resistance affect user performance. The present study investigated the performance of 11 individuals during constant load, demanding work to exhaustion while wearing respirators with eight different combinations of inhalation and exhalation resistance. Exercise performance time, performance rating, minute volume, and peak inspiratory and expiratory airflow were recorded at the end of each test trial, and independent correlations with inhalation resistance and exhalation resistance were assessed. The combined impacts of respirator inhalation and exhalation resistances were quantified as the total external work of breathing (WOBtot) and correlations between the test variables and WOBtot were also examined. Significantly linear decreases in performance were found with increased inhalation resistances independent of exhalation resistance (R2 = 0.99; p<0.001) and with increased WOBtot (R2 = 0.92; p<0.001). Performance also decreased with increased exhalation resistance but no significant relationships were found. Minute volume decreased linearly with increased inhalation resistance independent of exhalation resistance (R2 = 0.99; p<0.001), but the linear decrease observed between minute volume and WOBtot was weak (R2 = 0.36; p<0.05). These findings suggest that WOBtot serves as a reliable estimate of the combined impacts of respirator inhalation and exhalation resistances on user performance during hard work, but that inhalation resistance alone serves as a better predictor of ventilation during respirator wear.
Keywords: breathing resistance, performance, respirator, work of breathing
Journal of Occupational and Environmental Hygiene, 2: 368-373
Arthur T. Johnson
Kathryn R. Mackey
William H. Scott
Frank C. Koh
Ken Y. H. Chiou
Stephanie J. Phelps
ABSTRACT
Sixteen subjects exercised at 80-85% of maximal aerobic capacity on a treadmill while wearing a tight-fitting, FRM40-Turbo Powered Air Purifying Respirator (PAPR). The PAPR was powered by a DC power supply to give flow rates of 0%, 30%, 66%, 94%, and 100% of rated maximum blower capacity of 110 L/min. As flow rate was reduced, so was performance time. There was a 20% reduction in performance time as blower flow changed from 100% to 0% of maximum. Significant differences in breathing apparatus comfort and facial thermal comfort were found as flow rate varied. It was concluded that inadequate blower flow rate decreases performance time, facial cooling, and respirator comfort.
Keywords: PAPR, respiration, respiratory protection
Journal of the International Society for Respiratory Protection, Vol. 22 Fall/Winter 2005
A. T. Johnson
F. C. Koh
W. H. Scott, Jr.
K. M. Mackey
K. Y. S. Chen
T. Rehak
ABSTRACT
It would be helpful if peak inhalation flow rates were characterized for respiratory design, testing, and use. However, peak flow rates depend strongly on the wearer and the type of work being performed. Instantaneous inhalation rates for subjects exercising on a treadmill have been measured for the following conditions: 1) at 80-85% max without a respirator, 2) at 80-85% max while wearing a breath-responsive PAPR (blower flow rate) and 3) at 100% max without a respirator. Instantaneous inhalation flow rates were found to vary greatly among subjects and at different times for each subject. Depending upon the time that any given flow rate can be sustained, peak flow rates can vary considerably. Instantaneous flow rates were recorded and classified according to 20 L/min ranges so that the flow rate distribution could be obtained. If flow rates in the top one percentile are defined as peak flow rates, then a peak inhalation flow rate of up to 359 L/min (BTPS) was measured for condition 1. Peak instantaneous (less than 1% of flow rates) recorded flows were even higher, up to 442 L/min (BTPS). A peak blower flow rate of up to 679 L/min (BTPS) was measured for condition 2. Flow rates recorded at 100% max were generally higher than flow rates 80-85% max , although this varied somewhat among subjects. A linear relationship has been found between peak flow rate and average minute volume, which can then be used in a procedure to calculate peak flow rates expected at any given work rate.
Keywords: peak inhalation flow rates, oxygen consumption, and respirators
Journal of the International Society for Respiratory Protection, Vol. 22 Fall/Winter 2005
A. T. Johnson
S. J. Phelps
W. H. Scott, Jr.,
F. C. Koh
ABSTRACT
The CSE SR-100 Self-Contained Self-Rescuer (SCSR) is intended to supply oxygen to wearers in hazardous atmospheres during emergency situations. Used properly, the wearer should only move slowly and cautiously in order for the SCSR to deliver oxygen for at least 60 minutes. It is possible, however, that during a dire emergency some wearers may try to stretch the capabilities of the SCSR beyond its limits. To investigate the consequences of doing so, one subject walked on a treadmill at five different work rates corresponding to 65, 70, 75, 80, and 85% of maximal oxygen consumption. Attainable run times with the SCSR were much shorter than they would have been without the SCSR, being 45.7, 40.5, 28.4, 10.4, and 6.5 minutes for the five work rates. The amounts of oxygen delivered to the subject were 88, 84, 63, 25, and 16 L. Additional generated oxgyen was lost to the atmosphere. It was concluded that using the SCSR outside of its recommended range incurs severe penalties.
Keywords: emergencies, hazardous atmospheres, oxygen consumptio
Journal of the International Society for Respiratory Protection, Vol. 22 Spring/Summer 2005
Katherine R. M. Mackey
Arthur T. Johnson
William H. Scott
Frank C. Koh
ABSTRACT
Loose fitting powered air purifying respirators (PAPRs) utilize a motorized fan to draw air through the respirator's air purifying elements, delivering clean air to the wearer through a face piece that does not form an airtight seal with the wearer's face. Potential for wearer exposure to contaminants may exist if the breathing rate of the wearer exceeds the airflow rate supplied by the PAPR fan. In such an instance, ambient air could bypass the filters and enter the mask, potentially exposing the wearer to contamination. This investigation assessed the extent to which over breathing occurred in the Centurion MAX loose fitting PAPR. Sixteen subjects exercised at 80-85% max on a treadmill while wearing the PAPR inside a Portable Breathing Chamber (PBC). All subjects inhaled more air than was supplied by the PAPR blower, and 17% of the breathing volumes exceed the 1.4 L dead volume of the PAPR face piece.
Keywords: respiration, flow rates, exercise, dead volume
Journal of the International Society for Respiratory Protection, Vol. 22 Spring/Summer 2005
Arthur T. Johnson
William H. Scott
Stephanie J. Phelps
David M. Caretti
Frank C. Koh
ABSTRACT
Comfort of respirators is an important determinant for their use in contaminated atmospheres. This study was intended to demonstrate the relationship between subjective comfort and resistance to inhalation air flow in the respiratory system (conventionally called "respiratory resistance"). Respiratory resistance was measured with the Airflow Perturbation Device, which is described briefly. Subjects sat quietly in a respirator with one of six resistance inserts, ranging from 0.2 to 33.3 cm H2O · sec/L, and breathed either through through their noses or mouths. In all instances but one, respirator comfort decreased as respiratory resistance increased, and for the one remaining instance, the trend was very slight. It was concluded that respirator comfort is affected by the respiratory resistance of the wearer.
Keywords: respirator comfort, respiratory resistance, airflow perturbation device
Journal of Occupational and Environmental Hygiene, 1:343-348
Joyce E. Rebar
Arthur T. Johnson
Estelle Russek-Cohen
David M. Caretti
William H. Scott
ABSTRACT
A group of subjects with a large range of facial characteristics was asked to breathe deeply while wearing a full facepiece respirator. The facial characteristics noted were head length, head depth, bizygomatic breadth, lip length, and Menton-Sellion length. External resistances to inhalation or exhalation were varied in each of the trials. The data collected were analyzed for possible correlation between facial characteristics and breathing resistance. Although respirator resistances were found to vary, no statistically significant correlation was found with anthropometric measurements.
Keywords: breathing resistance, facial measurements, respirator mask
AIHAJ 62:685-688 (2001)
Arthur T. Johnson
William H. Scott
Karen M. Coyne
Frank C.S. Koh
Joyce E. Rebar
ABSTRACT
Previous work showed that telephone communications while wearing military respirators degraded both word comprehension and recognition speed. In addition, electronic amplification of the speech diaphragm signal had shown no advantage to the extra hardware. This experiment was performed to test effects of different configurations of commercially available respirators on telephone communications accuracy and speed. Twelve pairs of subjects were separated into different rooms and communicated by telephone. Modified rhyme-test words were presented by computer to the speaker, who transmitted the word by telephone to the listener. During the first replication, subjects were given no instruction about telephone communications procedure. During the second replication subjects followed a communications protocol that instructed them when to move the telephone handset from their ears to their mouths. Results showed that the protocol uniformly improved communications accuracy without incurring any extra time penalty. Word comprehension was still twice as fast without a respirator as with a respirator. Accuracy with the protocol nearly equaled the no respirator control value for most respirators tested.
Keywords: respirators, telephone communication
AIHAJ 62:411-415(2001)
David M. Caretti
William H. Scott
Arthur T. Johnson
Karen M. Coyne
Frank Koh
ABSTRACT
This study evaluated performance of individuals exercising at a fixed workload and wearing full-facepiece respirators modified to provide expiratory resistances of 0.27, 0.47, 1.81, 4.43, and 12.27 cmH2O · s · L-1. On five separate occasions, 15 volunteers exercised to voluntary endpoint on a treadmill at fixed speeds and grades chosen to elicit 85% of maximal aerobic capacity for an unencumbered condition. Exercise performance time was recorded at the cessation of each test. Results showed that performance time decreased linearly (R2 = 0.79; p<0.001) with increased resistances, and no threshold value below which expiratory resistance has no impact on performance was found. Average oxygen consumption rates and minute ventilation also decreased linearly with increased expiratory resistances, indicating that increases in expiratory resistance result in a considerable level of hypoventilation. From the perspective of respirator design, the results of this study suggest that the only practical expiratory resistance level limitation is the reduction in performance that will be acceptable to the end users.
Keywords: respirator, exhalation resistance, work
Journal of the International Society for Respiratory Protection, Spring 2000
Arthur T. Johnson
William H. Scott
David M. Caretti
ABSTRACT
Recent experiments relating performance to respirator resistances and dead volumes have been reviewed. Effects of each of these were most pronounced at very high work rates, where there were linear relationships between performance times and resistance or dead volume levels. There did not appear to be any threshold levels of resistances or dead volumes below which there were no performance effects. Thus, no optimum target values could be identified.
Journal of the International Society for Respiratory Protection, Spring 2000
Arthur T. Johnson
William H. Scott
David M. Caretti
ABSTRACT
Several recent experiments meant to quantify effects of respirators on speech transmission accuracy and speed have been reviewed. Results show that word comprehension was much better when a meaningful context is supplied with the word than if the word was used by itself. Speech comprehension decreased rapidly with distance between speaker and listener for single spoken words, and use of hand signals should be considered. During face-to-face communications, the speech diaphragm improves accuracy by about 3%. When a telephone was used as the speech transmission medium, the respirator speech diaphragm was found to improve accuracy by about 5%. There was no advantage to electronic amplification of speech. Using a communications protocol to signal movement of the handset from the mouth to the ear improved accuracy to nearly the level of the no-respirator control, but did not change recognition time.
AIHAJ 61:264-267 (2000)
Arthur T. Johnson
William H. Scott
Christopher G. Lausted
Karen M. Coyne
Manjit S. Sahota
Monique M. Johnson
Grace Yeni-Komshian
David M. Caretti
ABSTRACT
Respirators have been found to degrade communication effectiveness when wearers speak face-to-face. However, little is known about communication effectiveness when using the telephone and wearing a respirator. Eleven pairs of subjects were asked to pronounce and identify words chosen from Modified Rhyme Test lists. Each word appeared on a computer screen in one room and the speaker said the word into the telephone. The listener in another room identified the word and typed it into a computer linked with the first. Subjects wore U.S. Army M40 full-facepiece air-purifying respirators with hoods. Three different speech diaphragm arrangements and two hood materials were tested. Results show that accuracy suffered by about 10% when respirators and hoods were worn compared with the control condition. Word identification speed was one-third to one-half of the control (no respirator or hood) condition depending on specific equipment worn.
Journal of the International Society for Respiratory Protection, Spring 1999
Arthur T. Johnson
William H. Scott
Christopher G. Lausted
Karen M. Coyne
ABSTRACT
It was shown in a previous paper that treadmill performance times of subjects wearing respirators decreased linearly with increasing inhalation resistance. To see if loose-fitting respirators with their ultra-low inspiratory resistances would, indeed give longer performance times, an experiment was performed using a Racal Air-Mate 3 Respirator. To contrast these results, a North #76008A, a U.S. Army M17 respirator, and a control condition were included. Average performance times with these respirators were found to be longer for the lower resistances, but standard deviations for the data were too large to allow statistical significance. It was also found that an educational videotape shown during treadmill walking did not statistically significantly affect performance time, as anticipated.
American Industrial Hygiene Association Journal 60:474-479 (1999)
Arthur T. Johnson
William H. Scott
Christopher G. Lausted
M. Benhur Benjamin
Karen M. Coyne
Manjit S. Sahota
Monique M. Johnson
ABSTRACT
Respirator inspiratory resistance can affect performance times, especially when the experiment is optimized to elicit respiratory stress. Twelve subjects performed on a treadmill at constant speeds and grades chosen to result in performance times of 5-15 min. Six levels of inspiratory resistance were used, ranging from 0.78 to 7.64 cm H2O·sec/L. The results showed that performance times decrease linearly with resistance level, and no threshold resistance value is apparent. Inspiratory resistance also induces hypoventilation, with lower minute volumes and lower oxygen consumption values at higher resistances. These trends are also linear. From these results, there is no value for inspiratory resistance that can be given as a design goal. Other parameters such as weight and space may dictate filter resistance values, and these, in turn, will lead to determined performance degradations.
American Industrial Hygiene Association Journal 59:257-260 (1998)
Karen M. Coyne
Arthur T. Johnson
Grace H. Yeni-Komshian
Cathryn R. Dooly
ABSTRACT
A respirator degrades speech intelligibility and thus interferes with the ability of the wearer to communicate. The magnitude of this degradation is not well-studied and can vary as a function of numerous parameters. This study investigated the performance degradation of speech intelligibility in low-level noise for different speaker-listener distances and message sets (single words or predictable sentences) that occurred while wearing a respirator compared with not wearing a respirator. Thirteen speaker-listener pairs with normal hearing and speech were used. Speaker-listener separation distances were 0.61, 1.22, 1.83, 2.44, 3.05, and 3.66 m (2, 4, 6, 8, 10, and 12 ft) for the respirator condition and 1.22, 2.44, 3.05, 6.1, 9.15, and 12.2 m (4, 8, 10, 20, 30, and 40 ft) for the no-respirator condition. The means of the scores were used to determine the speech performance rating for both the single-word and sentence comprehension tests. The performance rating expresses the percentage of performance that can be expected while wearing a respirator compared with not wearing a respirator. Scores were interpolated linearly at distances at which no data were obtained. As expected, the speech performance rating was higher for the sentence comprehension test than for the single-word comprehension test at each distance. At a distance of 12.2m, the speech performance rating for the sentence comprehension was 70%. For the single-word comprehension test, the speech performance rating was zero for distances greater than 9.1m.
Keywords: respirators, speech and hearing, speech intelligibility
American Industrial Hygiene Association Journal, 58:881-884 (1997)
Arthur T. Johnson
William H. Scott
Karen M. Coyne
Manjit S. Sahota
M. Benhur Benjamin
Patricia L. Rhea
Gregory F. Martel
Cathryn R. Dooly
ABSTRACT
The accumulation of sweat inside a full-facepiece respirator mask and the rise in facial skin temperature can be important factors for acceptability of respirators worn in the heat. This study questioned how much sweat would have to be removed from a respirator (if a design to remove accumulated sweat were possible). Results from 20 subjects sitting in a warm, humid environment (35oC and 90% relative humidity) for 90 minutes indicated that the average value was about 0.203 g sweat/min from the face, head, and neck, with most of that coming from the neck region. Men were found to have higher sweating rates than women. The results indicate that a large amount of sweat could accumulate inside the mask over a typical 8-hour day. Average facial skin temperature was found to rise about 20oC over the 90-minute test, and this rise could likely be the cause of the very uncomfortable rating given to the respirator.
Keywords: heat stress, personal protective equipment, perspiration, respirators
Journal of the International Society for Respiratory Protection, Volume 15(1) Spring 1997
Arthur T Johnson
Cathryn R. Dooly
Karen M. Coyne
Manjit S. Sahota
M. Benhur Benjamin
ABSTRACT
Exhaling through the inspiratory filters of an air-purifying respirator mask could potentially increase the capacity of the filter to remove 5-10 times the amount of airborne contaminant compared to a filter with unidirectional flow. To test whether humans can tolerate exhaling through a high resistance, ten subjects were tested walking on a treadmill at a constant work rate designed to elicit 75-80% of their maximum heart rates. They wore no mask, a standard M17 full-facepiece mask, and an M17 mask modified so that both inhalation and exhalation flows went through the filters. Three of the subjects could perform no work while wearing the modified mask, and the remainder could perform only about 25% of the work that they could while wearing the standard mask.
American Industrial Hygiene Association Journal 58:578-582 (1997)
Arthur T. Johnson
Cathryn R. Dooly
Manjit S. Sahota
Karen M. Coyne
M. Benhur Benjamin
ABSTRACT
Previous testing has shown that visual acuity greatly influences task performance at light work rate levels. At moderate to heavy work rates, however, the Performance Rating Table (PRT) predicts almost no visual acuity effect. This experiment was performed to determine if the PRT value is realistic. Ten subjects walked on a treadmill at 75-80% of their maximum heart rates until their voluntary end points. Subjects wore various masks of the same kind, each with a different set of clouded lenses. Visual acuities, as measured on the Snellen eye chart, were measured before, during, and after exercise. It was found that visual acuity did not influence performance time, and that an average value for a performance rating of 91 must have been influenced by other mask factors besides visual acuity. These other factors are most likely respiratory stress, thermal stress, and other vision elements. The full-facepiece masks used in this study adversely affected visual acuity by about three-quarters of a Snellen line during exercise. Postexercise visual acuities were found to first decrease below pre-exercise values, then become better than pre-exercise values, then decline asymptotically to pre-exercise values.
Keywords: exercise, respirators, visual acuity
American Industrial Hygiene Association Journal 58:345-353 (1997)
Arthur T. Johnson
Cathryn K Dooly
David M. Caretti
Michal Green
William H. Scott
Karen M. Coyne
Manjit S. Sahota
Benhur Benjamin
ABSTRACT
A study was performed to test the effects of fatigue and food deprivation on performance while wearing respirator masks. Eleven subjects performed cognitive, psychomotor, and motor tasks, arranged in blocks of 3 hours and performed in round-robin sequence. Performance data and additional psychological and physiological information were obtained. Respirator masks were found to have little effect on task performance even with food intake denied. Fatigue and food deprivation had little effect on performance in the unmasked condition. The only measure that reflected fatigue effects was the psychological profile of mood states. An ancillary study involving five subjects who were allowed to ingest food during the day did not show any performance improvement over subjects without food.
Keyword: cognition, fatigue, mood, respirators, work performance
Eur J Appl Physiol (1996: 73:311-316)
Cathryn R. Dooly
Arthur T. Johnson
Charles O. Dotson
Paul Vaccaro
Paul Soong
Respirator masks vary in inhalation and exhalation resistance, and in dead volume. It is believed that these factors may contribute significantly to an early anaerobic threshold in mask wearers during maximal exercise. Very little is known about the effect of respirator masks on maximal oxygen consumption (VO2max) and the lactate threshold (LT). The purpose of the present study was to assess peak VO2 (VO2peak), LT and the ventilatory threshold (VT) of 14 experienced cyclists performing two maximal cycle exercise protocols while wearing a full respirator mask (FM) (M17 type) and a mouth mask (MM). VO2peak was 10% lower under FM conditions. Peak values for ventilation (VEpeak), respiratory rate (fbpeak) and tidal volume (VTpeak) were all significantly lower with FM versus MM conditions. Performance time and maximal heart rate (fcpeak) were not different between mask conditions. The LT and VT when expressed in % VO2peak, and the lactate concentration (mmol.l-1) at LT and VT were not significantly different across mask conditions. Bland-Altman plots demonstrated longer inhalation times, decreased fr values and greater oxygen extraction under FM conditions. Thus, perhaps due to the increased inhalation resistance of the FM condition, subjects were unable to attain their "normal" VO2 despite similar performace times and maximal fc. Furthermore, despite a diminished VO2peak with FM, LT and VT appeared to be the same as with a MM.
Key words: Threshold, ventilation, resistance, lactate, exercise
Journal of the International Society for Respiratory Protection, V13(2):8-22, Summer 1995
Arthur T Johnson
Cathryn R. Dooly
ABSTRACT
Once it has been ascertained that respirator masks provide sufficient protection against airborne contaminants, attention must turn to reduction of the physiological burden imposed on mask wearers. Mask designers need the design tools to produce new masks specifically meant to reduce this burden. Although masks have been used for over seventy years, there is very little basic information in quantitative form that can be used by mask designers to incorporate physiological effects into their designs. The ultimate goal, with accumulation of this type of information, is a computer-aided design process that eliminates the fabrication of prototypes that don't show promise for success in meeting design goals. This review demonstrates progress toward the ultimate goal.
Am. Ind. Hyg. Assoc. J. 56:858-865 (1995)
Arthur T. Johnson
Cathryn R. Dooly
Cassandra A. Blanchard
Elizabeth Y. Brown
ABSTRACT
Work performance of mask wearers has been shown to be less than performance of the same individuals without masks. How much this performance decrement is attributable to psychological factors was the subject of this study. This experiment was designed to give quantitative information about the effect of anxiety level on relative work performance while wearing a respirator mask. Twenty subjects were tested for trait anxiety levels and performed on a treadmill at 80-85% of their maximum heart rates until they reached voluntary end-point. Physiological, metabolic, and subjective measurements were taken every minute. While experimental variability precluded many of the results from achieving statistical significance, performance times with the mask averaged less than without the mask. Anxious subjects experience more discomfort, perform for shorter times, and accomplish less total work than their lower anxiety counterparts, even when rate of work can be adjusted.
Am. Ind. Hyg. Assoc. J. 56:467-473 (1995)
Arthur T. Johnson
Cathryn R. Dooly
Charles O. Dotson
ABSTRACT
To test effects of respirator masks on maximum oxygen uptake, ventilation threshold, and lactate threshold, 14 subjects underwent incremental bicycle exercise with and without masks. There was a statistically significant difference in final oxygen consumption between the two conditions, but other results suggest that the physiological measure of maximum oxygen uptake was not reached at termination for the full-mask condition. Lactate and ventilation thresholds were not affected by mask condition. Hypoventilation while wearing masks caused higher amounts of blood lactate accumulation. The resulting higher mask CO2 levels and lower O2 levels, normally attributed to mask dead volume, may instead be due to mask resistance.
Military Medicine, 159, 5:408, 1994
Cathryn R. Dooly
Arthur T. Johnson
Elizabeth Y. Brown
ABSTRACT
The purpose of this investigation was to determine performance decrement due to altered vision while wearing a respiratory face mask. Lenses clouded to visual acuities of 20/64, 20/38, 20/34, 20/28, 20/23, 20/20, and 20/15 were applied to each mask while subjects performed a battery of vision tests involving tracking and hand-eye coordination skills. Generally, performance decrement followed a significant curvilinear pattern as visual acuity worsened. These findings warrant the need to investigate the transfer of this performance decrement to skills that are inherent to military-type tasks.
Am. Ind. Hyg. Assoc. J. 55(9):818-822 (1994)
Arthur T. Johnson
Cathryn R. Dooly
Elizabeth Y. Brown
ABSTRACT
Forty-six subjects were required to perform a console-monitoring and two hand-eye coordination tasks while wearing masks with lenses clouded to give seven levels of visual acuity. The console-monitoring task performance was found to be the most sensitive to visual acuity, followed by the random hand-eye coordination task. These results can be used to help predict performance degradation when lenses become clouded due to condensation or particulate deposition.
Military Medicine, 158,10:665,1993
Arthur T. Johnson
Corey M. Grove
Ronald A. Weiss
ABSTRACT
The Performance Rating Table (PRT) is introduced as a means to separate mask-wearer performance by causative factors. The PRT shows which mask factors require design attention and how the mask affects different users.
Am. Ind. Hyg. Assoc. J. 54(12):749-751 (1993)
Arthur T. Johnson
Corey M. Grove
ABSTRACT
The respirator performance rating table (PRT) scheme has been offered as a way to organize physiological information to be useful for mask design. Designers do not usually deal exclusively with one kind or another of mask physiological effect. This paper presents normal mask design modules and how they relate to mask physiological effects as given in the PRT.
Am. Ind. Hyg. Assoc. J. 53(9):548-555 (1992)
Arthur T. Johnson
Corey M. Grove
Ronald A. Weiss
ABSTRACT
Respirator performance rating tables have been constructed for hot, humid (29oC, 95% RH); hot, dry (49oC, 30% RH); and cold, dry (-32oC, 70% RH) conditions. These tables convey expected wearer performance percentages compared to unmasked workers for various mask elements and work rates. The hot, humid condition was found to be the most severe overall. Many table entries approach 100%, thus leading to difficulties in correcting mask deficiencies.
Am. Ind. Hyg. Assoc. J. 53(3):193-202 (1992)
Arthur T. Johnson
Ronald A. Weiss
Corey Grove
ABSTRACT
The ultimate goal for respirator mask designers is computer-aided design. Mask design, however, is a very complex operation, with many different interrelationships. Current knowledge does not allow significant incorporation of physiological information into mask design. Rather, physiological information is usually gathered during mask evaluation, after the design process has been completed. The Performance Rating Table (PRT) is a beginning step to formulating physiological knowledge in a way that can be useful for design. The PRT organizes physiological knowledge to assign performance data to various mask and level of work causes. Best estimates of tabled values were obtained from the literature.
Am. Ind. Hyg. Assoc. J (42), October 1981
Arthur T. Johnson
Richard H. McCuen
ABSTRACT
Four competing models were developed to test assumptions about the workings of the respiratory controller. These models were tested against previously published data and unknown parameters estimated with a least-squares procedure. It was found that similar fits were obtained on data from men not at exhaustion by minimizing total respiratory power or inspiratory power only. Inspiratory power alone gave good fit at exhaustion. Also, mask resistance was found to be unequivalent to respiratory resistance in determination of respiratory period.
IEEE Transactions of Biomedical Engineering Vol. BME-27, No. 8, August 1980
Arthur T. Johnson
Richard H. McCuen
ABSTRACT
Four competing models were tested to determine which model assumptions were necessary to successfully predict respiratory period. Data from a number of sources were used to calibrate the models. All models were found to be sensitive to data inhomogeneity. Minimization of total respiratory power and inspiratory power was found to yield nearly equivalent results except where a limitation on exhalation time forced expiratory power to be nonminimal. Inclusion of negative work is a necessary basic assumption. Mask resistance appears to be only half as effective as internal resistance in determining respiratory period. Values for respiratory system parameters were determined and these varied with conditions under which data were collected.
Am. Ind. Hyg. Assoc. J. (39) October, 1978
Arthur T. Johnson
ABSTRACT
In order to test whether minimum exhalation time could be predictably classified according to age and sex, four groups of subjects representing young and old, men and women exercised on a treadmill until their voluntary end points. No group differences are apparent, although this could be due to subject selection. Minimum exhalation time did not appear to be reached at the point where exercise became anaerobic.
American Industrial Hygiene Association Journal, 37(8) 1976
Arthur T. Johnson
ABSTRACT
Experimental data further defining the region of predominant respiratory stress is presented. Within this region, energy requirements of respiration increase disproportionately to the overall energy expenditure of the body as exercise intensity increases. Addition of a mask accentuates this tendency, especially since no physiological compensation is possible in mask parameters. Mask technology has improved masks to the point where they no longer dominate the man-mask system, but instead contribute resistances and dead volumes approximately equal to those naturally occurring in man. Modeling based on minimization of respiratory energy rate of expenditure in the human is applied to this man-mask system and predictions are made which to this point have been nearly impossible to obtain from experimental data.
AIHA Journal Vol. 36, No. 3, March 1975
Arthur T. Johnson
Edmund G. Cummings
ABSTRACT
Mask design should be based more strongly on physiological data obtained from working individuals. This paper is a compendium of pertinent information as well as a guide to better design. An indication of the trends of current research is also given.
Edgewood Arsenal Technical Report ED-TR-74081, January 1975
Edgewood Arsenal, MD 21010Arthur T. Johnson
ABSTRACT
A hood fabricated from twill cloth, MIL-C-81280B, with air permeability of 175 cu ft/sq ft/min of 0.5 inch of water was evaluated by comparison with the standard M6A2 impermeable hood and no hooded condition. Men walked for 6.5 miles at an average rate of 2.5 mph in a hot environment with average wet-bulb globe temperature between 81o and 87oF. Twelve replications were performed. The permeable hood was found to be statistically different from either impermeable hood or no hood. Very little operational advantage can be gained, however, by depending solely on the impermeable hood to remove excess heat.
American Industrial Hygiene Association Journal, Vol. 35, No. 8, August 1974
Arthur T. Johnson
Howard M. Berlin
ABSTRACT
Exhalation time has been determined to be a rapid and reliable measure of the state of respiratory exhaustion of a working individual. Values of exhalation time obtained for healthy, young men during exercise decreased in value until a minimum was reached at the limit of their endurance. Although the average values varied somewhat among subjects, exhalation times at exhaustion for a particular individual were found to be very consistent, the standard deviation being approximately 10% of the mean. The average minimum value of 0.66 sec for 18 subjects appeared to be independent of inhalation resistance over the range of .11-.66 mm H2O-min/liter at 0.22 mm H2O-min/liter exhalation resistance. Exhalation time at exhaustion also appears to be independent of exhalation resistance over the range of 0-0.6 mm H2O-min/liter.
Edgewood Arsenal Technical Report ED-TR-73059, December 1973
Edgewood Arsenal, MD 21010
Arthur T. Johnson
Howard M. Berlin
ABSTRACT
Interaction between the effects of respiratory stress and thermal stress has been objectively identified. Analyses of data on distance run, percentage of inspiration at termination, and respiration rate at termination indicate the low value of resistance, 0.1 mm H2O-min/liter, to be the point at which interaction occurs. The heat load value causing interaction is somewhat equivocal. A model has been proposed which is consistent with our results and which defines the stress limitation for different rates of exercise. With the use of this model, the value of 0.1 mm H2O-min/liter has been objectively defined as the minimum effectual protective mask airflow resistance. Evidence is presented for exhalation time as the index of the respiratory stress limitation.
Edgewood Arsenal Technical Memorandum EATM 2300-3, April 1972
Edgewood Arsenal, MD 21010
Arthur T. Johnson
ABSTRACT
Tests were conducted to determine whether M17 protective-mask high-frequency airflow impedance decreased the airflow harmonic content of a subject exercising while wearing the mask. It was discovered that wearing the mask does, indeed, decrease airflow harmonics, but a check of mask high-frequency impedance shows no increase in the region of interest. It was concluded, therefore, that for this subject the breathing pattern produced was different with and without the mask, possibly leading to some adverse subjective response, but that the cause is likely breathing resistance, per se, rather than an increase in resistance with frequency.