107
CORRELATION BETWEEN PSYCHOLOGICAL TYPE AND PERFORMANCE TIME WHILE WEARING A
RESPIRATOR.
A. Johnson, F. Koh, W. Scott, University of Maryland, College Park, MD.
The brain efficiently utilizes dominant templates to think, learn, create, solve problems, and communicate. Many studies have shown that individuals perform better if not wearing a respirator than with wearing a respirator. This study examined the degree of performance reduction attributable to specific dominant character traits. The subjects performed on a treadmill at a constant speed and grade resulting in 80–85% VO2 max. A modified M40 respirator was used to create three levels of inspiratory resistance of 2.8, 16.8, and 27.3 cm H2O*sec/L. The 31 subjects were tested using a Myers-Briggs Type Indicator (MBTI) and State-Trait Anxiety Inventory (STAI). Multiple regressions and an ANOVA were used to test for correlation. When air intake is very constricted, sensing-intuition (how one takes in information), thinking-feeling (how one makes a decision), and Trait Anxiety become the components that reduced performance time. Trait STAI and MBTI can be used as predictors for performance time under high inspiratory resistance.
108
INSPIRATORY FLOW RATES DURING HARD WORK WHEN BREATHING THROUGH DIFFERENT
RESPIRATOR INHALATION AND EXHALATION RESISTANCES.
K. Coyne, D. Caretti, U.S. Army Edgewood CB Center, Aberdeen Proving Ground, MD; A. Johnson, University of Maryland, College Park, MD.
Flow rates currently used in respirator certification testing may substantially underestimate real world values. This study investigated the inspiratory flow rates of 11 volunteers exercising on nine occasions at 80–85% of maximal aerobic capacity while wearing an air-purifying respirator with modified inhalation (1.61, 5.27, and 12.86 cm H2O/L/s) and exhalation (1.01, 1.69, and 4.75 cm H2O/L/s) resistances. Data were sampled at 50 Hz. Peak flow rate (PF) and minute ventilation (VI) were determined for each inhalation and were compared among respirator conditions grouped either by common inhalation or exhalation resistance. Instantaneous flow rates (IF) were calculated. Data from all conditions were pooled and the percent of time was determined that IF and VI exceeded NIOSH respirator test standards of 64, 85, and 100 L/min constant flow and 40 L/min breather flow.
Peak flow rates decreased significantly from 240 ± 64 L/min for the lowest inhalation resistance to 178 ± 57 L/min for the highest resistance while VI decreased from 85 ± 23 to 60 ± 12 L/min. Increasing exhalation resistance had a similar effect. For all conditions combined, PF averaged 215.6 ± 65.0 L/min and VI averaged 76.0 ± 22.0 L/min. Instantaneous flow rates exceeded 64, 85, and 100 L/min for 48% ± 7%, 42% ± 8%, and 37% ± 12% of the time, respectively, while VI exceeded 40 L/min 99.9% of the time. Further analysis showed that VI exceeded 130 L/min 0.9% of the time while IF exceeded 400 L/min less than 0.1% of the time.
Increasing inhalation or exhalation resistance decreased PF and VI during strenuous exercise, but these still exceeded flow rates of current test standards. Testing filters at a 130 L/min breather flow would encompass 99.1% of minute ventilations and 99.9% of instantaneous flow rates recorded during this study and would more accurately simulate human respiration.
109
MEAN AND MAXIMUM PEAK INSPIRATORY FLOW VALUES AND DURATIONS IN NORMAL ADULTS
EXERCISING AT LIGHT, MODERATE, AND HEAVY WORKLOADS.
P. Cassidy, N. Anderson, L. Janssen, 3M Company, St. Paul, MN; D. Dengel, C. Kaufman, University of Minnesota, Minneapolis, MN.
Although research has been conducted on maximal minute ventilation, forced expiratory volumes, peak expiratory flows, and peak inspiratory flow (PIF) values, little work has focused specifically on quantifying the mean and maximum durations of sustainable PIF as well as defining the typical inspiratory breathing patterns exhibited when persons exercise at different work rates. The objective of this study was to quantify the characteristics of human ventilation, particularly mean and maximum instantaneous flows, flow rates, and durations of inspiratory flow in normal adults working at light, moderate, and heavy workloads. Fifteen subjects (nine male, six female; ages 20–65 (43.1)) participated in a graded exercise test to determine their aerobic capacities (VO2 max) using a Medical Graphics CPX/D metabolic gas exchange system. Results from the VO2 max tests were used to establish each subject’s light, moderate, and heavy workloads. The tests were then repeated at 40, 60, and 80% of VO2 max. Measurements of minute ventilation and peak inhalation flows were recorded when each subject had established steady-state for each of the three workload levels. Data analysis was then conducted for each workload level to determine means, maximums, and the ranges of: minute ventilation, maximum peak inspiratory flow, mean peak inspiratory flow, breath frequency, breath cycle time, mean inhalation time, duration of sustained peak inspiratory flow, and mean sustained peak inspiratory flow. Statistical analysis of differences among groups was performed, and generalized breathing patterns for light, moderate, and heavy workloads were calculated. Results for minute ventilation and peak inspiratory flows were consistent with those of previous research. The significance of the research findings are presented in the context of the design and testing of respiratory protective equipment.
110
MODEL OF EXERCISE PERFORMANCE WHILE WEARING A RESPIRATOR.
A. Johnson, Y. Chou, University of Maryland, College Park, MD.
A mathematical model of the physiological response to respirator wear during exercise has been constructed. The model predicts transient respiratory responses well. Oxygen consumption, minute volume, and exercise performance time are the main parameters predicted. The model gives good agreement for average responses, but predictions can differ considerably from data from individuals.
111
OXYGEN AND CARBON DIOXIDE LEVELS DURING QUALITATIVE RESPIRATOR FIT TESTING.
E. Laferty, USAF, Hickam AFB, HI; R. McKay, University of Cincinnati, Cincinnati, OH.
When conducting some types of qualitative respirator fit testing, workers often comment regarding the air inside the enclosure being hot and uncomfortable. In other cases, the person inside the enclosure may not be able to tolerate the environment and terminate the test prematurely. This leads to the question: What are the actual environmental conditions inside the enclosure? This study was designed to quantify oxygen and carbon dioxide levels and other parameters that might lead to these comments when following Occupational Safety and Health Administration accepted protocols for qualitative fit testing using Sweetener or Bitrex. For this study, subjects performed a series of four respirator fit tests. Testing was conducted while wearing two types of respirators (N95 filtering facepiece and a full face). Each was tested quantitatively and qualitatively. Parameters measured included subjects’ height, weight, age, oxygen and carbon dioxide levels, air temperature, heart rate, arterial oxygen saturation, and Borg Ratio Scale value on breathing exertion. Results from this study revealed that the mean level of CO2 inside the N95 filtering facepiece during qualitative fit testing was 4.2% and the mean oxygen level was 15.5%. The significant rise in carbon dioxide and reduction in oxygen may be responsible for many of the subjective complaints observed with this method of fit testing. Professionals conducting respirator fit tests should be aware of the physiological burdens that may occur during the qualitative respirator fit test. Some groups may be especially sensitive to this test such as the elderly, pregnant women, persons with pulmonary and/or cardiac disease, or persons with psychological disorders such as anxiety, panic disorders, or claustrophobia.
112
HOW FAR CAN ONE WALK WEARING A SCSR?
A. Johnson, W. Scott, S. Phelps, University of Maryland, College Park, MD.
Self-contained self-rescuers (SCSRs) are compact metal cases containing chemicals that can generate breathable oxygen during emergency egress in Immediately Dangerous to Life and Health (IDLH) atmospheres. They are routinely issued to miners for use during emergencies. SCSR oxygen generation can last a minimum of 60 min. SCSRs have a limited capacity to generate oxygen, and so users are instructed to walk at a vey measured pace in order that their needs for oxygen do not outstrip the rate of generation. When walking at the maximum rate allowed by the SCSR, how far can a wearer walk? Tests were conducted on a treadmill wherein subjects walked at a self-regulated pace at 0% grade. At the end of the test session, when the subject could no longer walk at even a minimal rate because of lack of oxygen, the speeds and times were multiplied and tallied to give total distance walked. This distance was consistently just over 4 mi in the 60 (plus) minutes. It might make sense to require multiple SCSRs for miners working over 4 mi from mine entrances. Also, the exothermic chemical reaction made the metal containers hot enough to burn the skin of wearers, and inhaled air temperature exceeded 50°C. Wearers need to be warned of these hazards.
113
ESTIMATING SERVICE LIVES OF ORGANIC VAPOR RESPIRATOR CARTRIDGES FOR MULTIPLE
VAPORS AT ALL HUMIDITIES.
G. Wood, Consultant, Los Alamos, NM; J. Snyder, NIOSH, Pittsburgh, PA.
A recently-published model for estimating service lives of organic vapor (OV) air-purifying respirator cartridges [Wood, JOEH 1:472–492 (2004)] has been extended to include multiple organic vapors at all humidities. Equilibriums among the OVs are calculated using Ideal Adsorbed Solution Theory, while the effects of adsorbed water are considered as due to micropore volume exclusion. Solubilities of OVs in water must also be taken into account. Adsorption kinetics include published effects of covapors and water vapor. The dynamics of adsorption and competition are incorporated using expanding zones, taking into account vapor and water displacements and rollups. A large number of measurements of breakthrough curves for OV mixtures at various humidities and for a single cartridge type have been done at NIOSH/NPPTL and by a contractor. The model, implemented as a spreadsheet and a computer program, has been tested against these data.
114
CONSTANT FLOW OR BREATHER FLOW THROUGH A CANISTER: DOES IT INFLUENCE THE
BREAKTHROUGH TIME?
L. Steenweg, M. Linders, S. van der Gijp, TNO-PML, Rijswijk, The Netherlands.
According to European standard EN 141, the capacity of canisters to be used for toxic industrial materials has to be tested at a constant flow of 30 litres per minute. According to the NIOSH requirements, canisters have to be tested at a constant flow of 64 litres per minute.
In actual use, however, the air flow pattern through a canister differs from constant flow: breathing results in a pulsating flow pattern. Air will pass the canister at variable speed during inhalation; this will result in much higher air flows through the canister. As a result, the breakthrough performance of the canister decreases dramatically. This means, in practice, that the canister can be used for short periods of time only; much shorter than the periods that are expected based on the outcome of tests with constant flow.
To establish the difference in breakthrough behaviour, TNO-PML has performed a research program in which ABEK-2 and NBC canisters were tested with 10 different toxic industrial materials under both breather flow and constant flow. All other parameters (influent concentrations, temperature, relative humidity, etc.) were kept the same.
In the presentation, the results will be presented and discussed, as well as the envisaged improvements/changes of standardisation.
115
EFFECT OF AEROSOL LOADING ON THE BREAKTHROUGH CHARACTERISTICS OF CHARCOAL
CARTRIDGE.
C. Chen, C. Lin, National Taiwan University, Taipei, Taiwan Republic of China; S. Huang, C. Chen, Institute of Occupational Safety and Health, Taipei, Taiwan Republic of China; Y. Kuo, Chung Hwa College of Medical Technology, Tainan, Taiwan Republic of China.
Organic solvents are often used in the work environment. Exposure to organic vapors may lead to adverse health effects of respiratory tract, kidney, cardiovascular, and nerve system. Charcoal cartridges are commonly used to protect against a wide range of organic vapors. Although most of the charcoal beds have a filter installed upstream to protect the activated charcoal from particle contamination, the information on the effect of aerosol loading on the charcoal cartridge performance was limited.
In this work, the cartridges filled with 36.5 g of activated carbon were challenged with 3000 ppm cyclohexane, with the test flow fixed at 15 L/min and the relative humidity at 50%. The monodisperse solid (acrylic) and liquid (DOP) challenge aerosols were generated by using a powder disperser and a condensation monodisperse aerosol generator, respectively. A flame ionization detector was used to monitor the cyclohexane concentrations upstream and downstream of the cartridge. The aerosol penetration through the charcoal cartridge was measured by using a scanning mobility particle sizer (< 0.7 µm) and an aerodynamic particle sizer (> 0.7 µm).
The results showed that the aerosol penetration through the charcoal cartridge was up to 80% around the most penetrating size, even though the breakthrough time was longer than 30 minutes when challenged with 3000 ppm cyclohexane. The pressure drop across the charcoal bed decreased with time when challenged with cyclohexane, and this air resistance “regained” if the clean air was used to remove part of the absorbed cyclohexane. The breakthrough time of charcoal cartridge decreased with increasing aerosol concentration. Liquid aerosols showed stronger effect (than solid particles) on reducing the absorbing capability of the charcoal bed, apparently due to more surface area to cover up the activate site of the charcoal.
116
COMPARING THE ADSORPTION CHARACTERISTICS OF A NEW COMPOSITE MATERIAL WITH
GRANULAR ACTIVATED CARBON.
C. Lungu, J. Park, University of Minnesota, Minneapolis, MN.
Granular activated carbon (GAC) has been the industry standard for many years as adsorbent in respirator cartridges. However, GAC presents a series of drawbacks for use in industrial hygiene: it has relatively low adsorption capacity, poor selectivity, high pressure drop, and requires containment, making the respirators expensive. Activated carbon fibers exhibit significantly better adsorption characteristics, but they are expensive and nondurable. In recent years a new family of adsorbent materials has been developed using glass fibers coated with phenolic resin which was activated. These new composite materials, Fibrous Porous Materials (FPM) are much less expensive than activated carbon fibers and have a higher mechanical resistance. However, their adsorption characteristics have not yet been tested for respiratory protection use. In this study, the dynamic adsorption of FPM was compared with that of GAC for three compounds: toluene, acetone, and sulfur dioxide. The adsorption isotherms of the three compounds were obtained from the breakthrough curves generated by continuous injection of the contaminants at controlled rates into the airflow passing through fixed beds of GAC and FPM. The adsorbent was placed into a copper cylinder immersed in a temperature controlled water bath. A gas chromatograph, or in the case of sulfur dioxide, an infrared gas analyzer, monitored the effluent concentration. For the entire range of toluene-challenging concentrations (25 to 200 ppm) the adsorption capacity was 85 to 129% higher using GAC compared with FPM. For acetone too, the GAC adsorption capacity was higher compared with FPM for all challenging concentrations (31 to 68%). Sulfur dioxide was also more strongly adsorbed by GAC compared to FPM; however, for this compound the shape of the breakthrough curve was almost identical, indicating similar kinetics. Although the FPM did not show improved performance compared to GAC, its adsorption characteristics should be further studied.
Posted May 30, 2005