The effect of respirator dead space and lung retention on exposure estimates.

This paper develops, tests, and applies equations that predict the magnitude of the effect of lung retention and respirator dead space on average inhalation concentration and other related quantities. The equations were validated by numerical simulation and experimental measurement with a respirator on a mannequin connected to a breathing machine. Experimental data are presented verifying the applicability of the equations. The authors present applications of the equations and procedures to various types of respirator performance measurements and to a predictive respirator performance model. Graphs are presented giving correction factors. In all cases the correction factors are less than 2. Under typical conditions of workplace protection factor measurement with half-mask respirators, average inhalation concentration will be 105% to 125% of full-cycle average concentration.

The role of industrial hygiene in preventing occupational lung disease.

This chapter examines the role of industrial hygienists in preventing pulmonary disease. As part of a team, these environmental specialists are trained to anticipate, recognize, evaluate, and control environmental health hazards in the workplace. Lung diseases, caused by exposure to airborne chemicals in the form of dusts, mists, gases, and vapors, are among the most serious health hazards facing industrial workers and consequently are an important consideration for industrial hygienists.

Aerosol penetration through respirator exhalation valves.

Exhalation valves are a critical component of industrial respirators. They are designed to permit minimal inward leakage of air contaminants during inhalation and provide low resistance during exhalation. Under normal conditions, penetration of aerosol through exhalation valves is minimal. The exhalation valve is, however, a vulnerable component of a respirator and under actual working conditions may become dirty or damaged to the point of causing significant leakage. Aerosol penetration was measured for normal exhalation valves and valves compromised by paint or fine copper wires on the valve seat. Penetration increased with increasing wire diameter. A wire 250 microns in diameter allowed greater than 1% penetration into the mask cavity. Dirt or paint accumulated on the exhalation valve allowed a similar level of penetration. Work rate had little effect on observed penetration. Penetration decreased significantly with increasing aerosol particle size. The amount of material on the valve or valve seat necessary for significant (greater than 0.5%) inward leakage in a half-mask respirator could be readily observed by careful inspection of the exhalation valve and its seat in good lighting conditions.

Performance of dust respirators with facial seal leaks: I. Experimental.

The ability of representative half-mask and single-use respirators with facial seal leaks to provide protection against aerosols was evaluated by experimental measurement. Respirators were mounted on a manikin in a test chamber and operated at seven steady flow rates over the range of 2 to 150 L/min. Samples of polydisperse and monodisperse aerosols were taken from inside and outside the respirator and analyzed by a calibrated optical particle counter over the particle-size range 0.1 to 11.3 microns. Measurements were made separately for filter performance as a function of particle size and flow rate, and simulated leak performance (penetration) as a function of particle size, pressure drop, and leak size. Flow rate vs. pressure drop measurements were made for all filters and leaks tested. For a given leak condition the percentage of the total flow traversing the leak varied several fold over the usual range of airflow rates through a respirator. Aerosol penetration was found to depend strongly on particle size and flow rate for filters, and to depend strongly on particle size and less strongly on pressure drop for leaks. One can conclude from these measurements that the aerosol-size distribution inside a respirator will nearly always be significantly different from that outside the respirator.

Performance of dust respirators with facial seal leaks: II. Predictive model.

A performance model for half-mask and single-use respirators is presented. It represents a possible alternative to field measurements of respirator performance. Experimental data on filter and leak performance given in Part I were used to develop a model that allows one to predict 1) the overall respirator penetration as a function of particle size for any work rate and 2) overall total mass penetration for any work rate and exposure aerosol-size distribution for a known respirator filter and facial seal leak condition. A simplified method based on general regression equations is presented that allows one to estimate these quantities based on QNFT (quantitative fit testing) measurements and a knowledge of the exposure aerosol-size distribution. Example calculations are given for a situation in which QNFT gives a fit factor of 50 for a half-mask with dust, fume and mist filter cartridges, but predicted protection factors for various use conditions range from 20 to 81 depending on exposure particle-size distribution and work rate of the wearer.

Exposure of firefighters to diesel emissions in fire stations.

Personal sampling techniques were used to evaluate firefighter exposure to particulates from diesel engine emissions. Selected fire stations in New York, Boston and Los Angeles were studied. Firefighter exposure to total particulates increased with the number of runs conducted during an 8-hr period. In New York and Boston where the response level ranged from 7 to 15 runs during an 8-hr shift, the resulting exposure levels of total airborne particulates from diesel exhaust were 170 to 480 micrograms/m3 (TWA). Methylene chloride extracts of the diesel particulates averaged 24% of the total. The authors' findings suggest that additional research is necessary to assess fire station concentrations of vehicle diesel exhaust that may have adverse health consequences to firefighters.

Effect of aerosol size on the blood lead distribution of industrial workers.

The size distribution measurements of lead aerosol from a brass foundry and primary lead smelter are used to simulate blood lead distributions applying a pharmacokinetic model developed by Bernard. The predicted distribution of blood lead levels determined using the actual size distribution of lead aerosol are compared to the blood lead levels predicted according to the model assumptions adopted in setting the OSHA lead standard. In the furnace area of the smelter and the pouring area of the foundry the predicted mean blood lead level is higher than that found in the standard whereas, in the smelter's sintering and mixing operation the blood lead level is less than that suggested by the standard. The data support the conclusion that size-selective sampling needs to be considered for incorporation into the OSHA lead standard.

Particle bounce in a personal cascade impactor: a field evaluation.

The collection characteristics of five types of substrates (collection surfaces) used in personal cascade impactors were evaluated for particle bounce in the laboratory with lead dioxide dust, and in the field with brass pouring fume and brass grinding dust. The substrates tested were uncoated stainless steel, silicon grease-coated stainless steel, oil-saturated Millipore membrane filter, oil-saturated Teflon membrane filter and oil-saturated sintered stainless steel. The use of coated and uncoated stainless steel plates to collect lead dioxide dust produced no difference in measured mass median diameter (MMD); however, with brass grinding dust, there was a 50% decrease in measured MMD when uncoated stainless steel substrates were used, as compared with coated stainless steel substrates. Oil-saturated Millipore membrane surfaces gave consistently lower MMDs than coated stainless steel surfaces. Coated and uncoated stainless steel gave similar MMDs when used to sample brass pouring fume. Oil-saturated Teflon membrane and oil-saturated sintered metal, surfaces for which the collection efficiency is presumed to be independent of the particle loading, gave MMDs similar to those measured for grease-coated stainless steel. The implications of these comparisons are discussed. It is concluded that bounce characteristics are strongly dependent on aerosol material and the suitability of collection surfaces needs to be determined by field evaluation.

Common materials for emergency respiratory protection: leakage tests with a manikin.

In areas where respirators are not routinely used, emergencies (such as fires) may occur in which protection from airborne particles is necessary. The following readily available materials were tested on a manikin connected to a breathing simulator to determine the fraction of an approximately 2-micron diameter aerosol that would leak around the seal between the materials and the manikin's face: cotton/polyester shirt material, cotton handkerchief material, toweling (a wash cloth), a surgical mask (Johnson & Johnson Co., Model HRI 8137), and a NIOSH-approved disposable face mask (3M Corp., Model #8710). The leakage tests were done to supplement the measurements of penetration through the materials reported previously. Leakage fractions were determined by comparing the penetration of the same aerosol for the materials held to the face versus being fully taped to the face. At a breathing rate of 37 liters per minute, mean leakages for the materials ranged from 0.0 percent to 63 percent, depending on the material. Mean penetrations exclusive of leakage ranged from 0.6 percent to 39 percent. Use of nylon hosiery material ("panty hose") to hold the handkerchief material or the disposable face mask to the face was found to be very effective in preventing leakage. Such a combination could be expected to reduce leakage around the handkerchief to about 10 percent or less in practice, and around the mask to less than one percent, which suggests the adaptation and use of such an approach for industrial hygiene.

Effect of plateout, air motion and dust removal on radon decay product concentration in a simulated residence.

The effectiveness of increased air motion and dust removal in reducing radon decay product concentration in residences subject to radon intrusion was evaluated in a 78-m3 room under steady-state conditions for air infiltration rates between 0.2 and 0.9 air changes per hour. Room-size, portable electrostatic precipitators and high-efficiency fibrous filters were tested as typical residential air cleaning devices; a portable box fan and a ceiling fan were employed as typical residential air movers. Reductions in working levels of 40-90% were found. The fate of radon decay products, with and without mixing fans, was determined by direct measurement. When mixing fans were used, most of the nonairborne potential alpha-energy was plated out on the room surfaces; less than 10% was deposited on the fan blades or housing. Results were compared to a mathematical model based on well-mixed room air, and good agreement was obtained.

Marijuana, tetrahydrocannabinol, and pulmonary antibacterial defenses.

Although marijuana is now consumed extensively, little is known of its biologic effects on the lung. To study this problem, the intrapulmonary inactivation of an aerosolized challenge of Staphylococcus aureus was quantified in rats exposed to graded amounts of fresh marijuana smoke. Controls inactivated 85.1 percent +/- 0.3 percent of the bacteria six hours after inoculation. Following an in vivo accumulative exposure to smoke from progressively increasing numbers of marijuana cigarettes for periods of ten minutes each hour for five consecutive hours, intrapulmonary bacterial inactivation was impaired in a dose-dependent manner. Evaluation of the effects of parenterally administered delta-9-tetrahydrocannabinol (THC) or of exposure to fresh smoke from THC-extracted marijuana placebo cigarettes indicated that the cytotoxin in marijuana was not related to the primary psychomimetic component. Thus, marijuana smoke is toxic to the lung and impairs the pulmonary antibacterial defense system in a dose-dependent manner.

Size characteristics of cigarette smoke.

The aerodynamic size distribution of cigarette smoke was measured using an aerosol centrifuge and a cascade impactor. The observed size distribution was log normal with an initial mass median aerodynamic diameter which decreased from 0.52 to 0.38 mu m as the dilution was increased from 10:1 to 700:1. The average geometric standard deviation was 1.38. The differences between these results and those reported by other investigators are attributed to differences in measurement methods.

The effect of chronic exposure to tobacco smoke on the antibacterial defenses of the lung.

To evaluate the effects of cigarette smoking on the host defenses of the lung, male CD rats were exposed to fresh whole smoke for up to 60 consecutive days. Intrapulmonary deposition of smoke and animal exposure levels, quantified with decachlorobiphenyl and other smoke tracers, indicated a daily cigarette exposure equivalent to approximately a pack and a half per day in man. Pulmonary alveolar macrophage function in situ was quantified by the inactivation of an aerosolized challenge of Staphylococcus aureus six hours after inoculation. Controls (n=120) inactivated 88.8+/-0.64% of the staphylococci. Exposure to whole smoke did not impair intrapulmonary antistaphylococcal defenses, with inactivation rates of 89.8+/-0.97% (n=49) and 89.1+/-0.46% (n=74) at 30 and 60 days, respectively. Inactivation distribution frequency analysis in controls revealed that 7% of animals had inactivation values greater than two standard deviations from the mean. With prolonged exposure mean with less skewing towards the abnormal. Alveolar macrophages harvested from smoked animals were comparable in viability and in vitro antistaphylococcal activity to controls, appeared to be metabolically activated and had specific stereologic ultrastructural alterations. These studies indicate that chronic exposure to tobacco smoke does not impair, and in fact may stimulate, the host defenses of the lung, as evaluated by in vivo and in vitro pulmonary alveolar macrophage function.