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The service life of organic vapor cartridges was determined for ten vapors at concentrations between 50 and 3000 ppm. The breakthrough time (tb) conformed to the empirical expression tb = aCf, where C is the concentration in ppm and a and be are constants. The average value for b at 10% breakthrough was -0.67 +/- 0.17. The service life is inversely proportional to flow rate for acetone and benzene.
Cartridge service life is not appreciably affected at relative humidities below 50%. However, performance is severely compromised when the humidity exceeds 65%. Experimental values are compared from those calculated from the adsorption isotherm, Mecklenburg and modified Wheeler equations. Calculations indicate that temperature does not play a significant role in service life predictions.
The performance of three commonly used chemical cartridge respirators for SO2 was measured under working conditions in a copper smelter. An effective SO2 protection factor for each man-respirator trial was calculated as the ratio between average SO2 concentrations sampled outside the respirator mask and that simultaneously sampled from inside the mask. The in-use SO2 protection afforded by the three respirators proved to be highly variable with mean protection factors of 22, 18, and 13. The distributions of the protection factors and the effects of mask type, facial size, and mask comfort are discussed.
Design and construction of a moderate-weight, battery-powered, positive-pressure respirator pack is described. Design detail of a two-stage air mover is given, along with its adaptation for use as a portable air sampler.
Six models of single-use dust respirators were evaluated for NaCl aerosol leakage while being worn by human test subjects. The respirators were evaluated for their ability to fit a wide range of facial sizes, for changes in efficiency after storage in a humid atmosphere; and for consistency of protection when worn for a six-hour work shift. Results indicate that only two of the six models tested provided a protection factor of 5 to all members of a 10 person test panel. Storage in a humid atmosphere had no detectable effect on five of the models, while one showed a decrease in the level of protection offered. Throughout a 6 hour work shift, four of the six models provided a consistent level of protection, while two showed variations in the level of protection offered.
Respirator cartridge service lives (1 ppm breakthrough) were determined for low level (approximately 10 ppm) exposures to vinyl chloride using simple apparatus and an infrared spectrophotometer. Two classes of organic vapor cartridges were tested; six brands which received approval from MESA-NIOSH before July 15, 1975 ahd two brands which were not approved but were available through local safety supply outlets on that date. Cartidges were tested both as they came from the supplier and after being preconditioned for 6 hours. Effects of insult concentration, preconditioning, and absorbent weight were investigated. No cartridge service life exceeded 1 hour; many did not provide protection for even 30 minutes. As a result, the use of cartridge containing half mask respirators for vinyl chloride exposure should be questioned.
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A LASL-developed sodium chloride aerosol filter penetration test has been compared to the silica-dust and silica-mist tests used by NIOSH for respirator approval testing. Filter discs were made from two types of resin impregnated electrostatic felt filter materials and tested at LASL for resistance to air flow and sodium chloride aerosol penetration. Sets of these filters were sent to four respirator manufacturing companies, where silica-dust and silica-mist penetration tests were performed. One set of filters was sent to NIOSH Division of Physical Sciences and Engineering in Cincinnati where sodium chloride aerosol penetration tests were performed by NIOSH personnel.
Respirators are currently approved by testing them on a number of subjects without specifying facial sizes. Anthropometrically designed test panels were developed that represent the majority of the working population in terms of relevant facial measurements.
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This study examined work tolerance and subjective responses while performing two levels of work and wearing four types of protective ensembles. Nine males (mean age = 24.8 years, weight = 75.3 kg, VO2 max = 44.6 ml/kg min) each performed a series of eight experimental tests in random order, each lasting up to 180 min in duration. Work was performed on a motor-driven treadmill at a set walking speed and elevation which produced work intensities of either 30% or 60% of each subject's maximum aerobic capacity. Work/rest intervals were established based on anticipated SCBA refill requirements. Environmental temperature averaged 22.6 degrees C and average relative humidity was 55%. The four protective ensembles were: a control ensemble consisting of light work clothing (CONTROL); light work clothing with an open circuit self-contained breathing apparatus (SCBA); firefighter's turnout gear with SCBA (FF); and chemical protective clothing with SCBA (CHEM). Test duration (tolerance time) was determined by physiological responses reaching a predetermined indicator of high stress or by a 180-min limit. Physiological and subjective measurements obtained every 2.5 min included: heart rate, skin temperature, rectal temperature, and subjective ratings of perceived exertion, thermal sensation, and perspiration. The mean tolerance times were 155, 130, 26, and 73 min, respectively, for the CONTROL, SCBA, FF, and CHEM conditions during low intensity work; and 91, 23, 4, and 13 min, respectively, during high intensity work. Differences between ensemble and work intensity were significant. FF and CHEM heart rate responses did not reach a steady state, and rose rapidly compared to CONTROL and SCBA values. SCBA heart rates remained approximately 15 beats higher than the CONTROL ensemble during the tests. At the low work intensity, mean skin temperatures at the end of the test were 32.7, 33.1, 36.7, and 36.3 degrees C, while mean core temperatures were 37.6, 37.9, 37.9, and 38.5 degrees C, respectively. The subjective data indicated that, in general, subjects were able to perceive relative degrees of physiologic strain under laboratory conditions. Wearing protective clothing and respirators results in significant and potentially dangerous thermoregulatory and cardiovascular stress to the wearer even at low work intensities in a neutral environment. Physiologically and subjectively, firefighter's turnout gear (the heaviest ensemble) produced the most stress, followed by the CHEM, SCBA, and CONTROL protective ensembles.
OBJECTIVE: Exercise-induced bronchospasm (EIB) has a prevalence of 6% to 7% in United States Army personnel and 3% to 13% in professional athletes. There are reported concerns that military personnel with EIB will have increased airway hyperreactivity or significant dyspnea while wearing the standard military M40 protective mask. The objective of this study is to determine whether the M40 protective gas mask increases airway hyperreactivity in military personnel with exertional dyspnea and the diagnosis of EIB. METHODS: Ten active duty military with EIB (defined as history of exertional dyspnea, normal spirometry, and reactive methacholine challenge test) and 10 normal control subjects were evaluated. Both the participants and control subjects underwent baseline exercise challenge testing (ECT) with and without the M40 protective mask. Forced expiratory volume in one second (FEV1) (percent predicted) post ECT was compared to baseline FEV1 within and between groups along with exercise time. RESULTS: There was no statistical difference in between individuals and between groups wearing the M40 mask. None of the study group had a positive ECT exercising without the M40 mask while 20% of the study group with EIB had a positive ECT wearing the M40 mask. CONCLUSION: Military personnel with EIB who exercised with the M40 protective mask did not overall have significantly increased airway hyperreactivity compared to control subjects. Screening ECT may be beneficial in identifying those susceptible persons who report symptoms while wearing the M40 protective mask.
Breakthrough curves of organic vapors through a charcoal bed are analyzed by a simplified Theory of Statistical Moments. It is shown that this theory adequately describes the dependence of the shape of the breakthrough curve on concentration of vapor, velocity of air, particle size of charcoal, and length of the bed.
NIOSH approves organic vapor respirator cartridges based upon testing against 1000 parts per million carbon tetrachloride vapors. Data for other organic vapors are necessary for proper use of organic vapor cartridge respirators against those vapors. This paper describes a system designed to test respirator cartridges and canisters and results of cartridge tests against benzene and acrylonitrile at a variety of concentrations.
Protection Factors provided by 25 NIOSH approved supplied-air respirators were determined while the devices were worn by a panel of test subjects anthropometrically selected to represent adult facial sizes. Polydispersed DOP aerosol was used for respirator fit tests on continuous flow, demand, and pressure-demand respirators. Based on facepiece leakage measurements it appears that demand-type respirators should neither be used nor approved. The highest level of protection was provided by pressure-demand devices.
The objective of this study was to determine the average reduction in inhalation exposures produced by intermittent use of filter cartridge respirators by cadmium workers. Inhalation exposure was estimated by measuring the cadmium concentration inside the respirator while it was worn or hanging around the worker's neck. Air concentrations of cadmium were measured simultaneously inside the respirator and at the worker's lapel with a dual sampling system. Each of nine workers were measured on three consecutive days for a full work shift. The average inhalation exposures ranged from 3 to 67 micrograms/m3 while the TWA lapel concentrations ranged from 19 to 3600 micrograms/m3; respirator use produced a substantial reduction in inhalation exposures when lapel concentrations were above 100 micrograms/m3. On the average, the inhalation exposure was 26% of the lapel concentration, but the effective protection varied widely between individuals and from day to day. If used cautiously, this relationship may be useful for estimating the approximate average inhalation exposure of a group of workers routinely using half mask respirators.
Occasionally, airborne contaminant concentrations cannot be reduced to desired levels, even after the installation of feasible engineering controls. The industrial hygienist may have to recommend full-shift or partial-shift use of appropriate respirators to reduce exposures. The method described allows the industrial hygienist to recommend the minimum period of time an exposed employee needs to use a respirator in order to reach the desired exposure level. The procedure is based on the calculation of Time-Weighted Averages, using the upper confidence levels of air sampling data, and the respirator protection factors.
Protection factors for one model of closed-circuit, pressure-demand, self-contained breathing apparatus were determined for eight volunteers while clean-shaven and at approximately two-week intervals during an eight-week, beard-growth period. Measurement of facepiece leakage was patterned after the DOP quantitative fit test method outlined in ANSI Z88.2-1980. Comparison of results indicated that beard growth had a profound adverse effect on the amount of protection provided.