Particulate Respirators Research Articles

Efficacy of three face masks in preventing inhalation of airborne contaminants in dental practice

BackgroundUp-to-date studies are needed on the protection provided by face masks used by dentists. We assessed the relative filtering efficacy of two currently used surgical face masks (one a molded mask, the other a tie-on mask) and a certified personal particulate respirator, all made by a single manufacturer.MethodsThe authors sprayed bicarbonate particulate against a porcelain surface (representing the patient's mouth) and collected it via a mannequin head (representing the dentist's head) placed 40 centimeters away and a tube with two airflow rates (0.5 cubic meters per hour and 9 m3/hour). They calculated the dry residue weight. They performed three separate runs for each mask and three runs with no mask at the two airflow rates with and without aerosol.ResultsWith no mask (control), the authors recorded significant weight gains at both airflow rates with and without vaporization. With vaporization, the three masks were associated with different dry residue weights (P < .03 with the Kruskal-Wallis test at both flow rates), the respirator providing the lowest amount. The respirator provided an efficiency of 94 to 96 percent, compared with 90 to 92 percent and 85 to 86 percent for the molded and tie-on surgical masks, respectively.ConclusionsThese data provide independent evidence that a certified personal respirator can be more effective than high-quality surgical masks in dental settings.Clinical ImplicationsDentists should be aware that a certified particulate respirator can provide them with superior filtering protection.

The Effect of Pressure Drop on Respirator Faceseal Leakage

Users of particulate air-purifying respirators are typically told to change their filters when breathing resistance becomes uncomfortable. It has been proposed that a noticeable increase in breathing resistance (pressure drop) may increase airflow through respirator faceseal leaks. This logic has been extended to suggest that respirator user exposure to contaminants may increase because of this theoretical increase in air leakage. Procedures similar to those of previous investigators were used to study this issue. Repeated faceseal leak rate measurements were made at –5.6 through –20.1 mm water pressure drops across the faceseal. Subjects were divided into two groups, representing acceptable fit or unacceptable fit, based on leak rate criteria prescribed by the Occupational Safety and Health Administration (OSHA). Subjects with acceptable fit did not experience an increase in faceseal leak rate with increased pressure drop. Leak rates for subjects with unacceptable fit were highly variable and did not show an association with pressure drop. Results of this study do not support the concept of increased faceseal leakage with increased pressure drop. The evidence does not suggest increased risk of contaminant exposure through the face seal as pressure drop increases.

Bioterrorism Drill in Illinois: A Systemwide Evaluation

BACKGROUND: In May 2003, the U.S. Department of Homeland Security conducted a bioterrorism drill. It was the first drill since September 11, 2001. Sixty-four hospitals in Illinois participated in this bioterrorism drill. METHODS: The infection control experiences of eight acute-care hospitals in one healthcare system in the Chicago area were collated from a questionnaire sent to the infection control professionals. RESULTS: The healthcare system consists of three community teaching hospitals and five community hospitals with an average daily census ranging from 79 to 586. The hospitals report to two independent federal health jurisdictions (Chicago Department of Public Health and the Illinois Department of Public Health) and three county health departments. The surge of patients seriously challenged the capacities of the hospitals. More than 300 patients (human and paper) were sent to the eight Emergency Departments during the drill. Approximately one-third of the patients had symptoms consistent with pneumonic plague. A number of patients were dead on arrival or expired soon after. All hospitals initiated appropriate isolation precautions. Symptomatic patients were placed on airborne precautions in negative-pressure rooms, and personnel wore N95 particulate respirators. Most hospitals switched to surgical masks once the health departments identified the agent. One site recorded an inadequate supply of personal protective equipment. Infection Control or Employee Health gave prophylaxis to exposed patients and personnel. Communication was a serious problem. The drill was primarily confined to the Emergency Departments, and communication with other departments, including Infection Control, was poor or nonexistent at most sites. Health departments and other outside agencies provided confusing and sometimes contradictory information. CONCLUSIONS: The major lesson learned was that there was inadequate communication to and from the health departments and within the hospitals. Confusion existed, despite advance knowledge of the biological agent. The drill interfered with actual patient care; however the experience was beneficial in preparing hospitals for a real bioterrorism event.

SARS among critical care nurses, Toronto.

To determine factors that predispose or protect healthcare workers from severe acute respiratory syndrome (SARS), we conducted a retrospective cohort study among 43 nurses who worked in two Toronto critical care units with SARS patients. Eight of 32 nurses who entered a SARS patient’s room were infected. The probability of SARS infection was 6% per shift worked. Assisting during intubation, suctioning before intubation, and manipulating the oxygen mask were high-risk activities. Consistently wearing a mask (either surgical or particulate respirator type N95) while caring for a SARS patient was protective for the nurses, and consistent use of the N95 mask was more protective than not wearing a mask. Risk was reduced by consistent use of a surgical mask, but not significantly. Risk was lower with consistent use of a N95 mask than with consistent use of a surgical mask. We conclude that activities related to intubation increase SARS risk and use of a mask (particularly a N95 mask) is protective.

Environmental agricultural tractor cab filter efficiency and field evaluation.

To evaluate filter efficiency and performance of environmental enclosures for tractors, 3- to 4-year-old tractor enclosure combinations (cabs retrofitted to tractors after manufacturing) were studied at a custom pesticide applicators facility. Optical particle counters were used to measure the aerosol number concentration inside and outside the cab. The ratio of these concentrations multiplied by 100 is termed percentage penetration, the amount of the aerosol that penetrates into the enclosure. For particles in the 0.3 to 0.4 microm range, penetration into the cab was reduced from 11 to 0.4% in the following sequential steps. First, manufacturing mistakes were corrected by fixing a bowed flange and inappropriate sealing of the sheet metal used to separate incoming air from air that had passed through the filter. This reduced aerosol penetration from 11 to 4.8%. Replacing gasket material on the used filter reduced penetration from 4.8 to 0.65%. This suggests that the filter gaskets are deforming and allowing leakage. Also, the filter media were evaluated for aerosol penetration as a function of particle size and were tested per the criteria stipulated in 42 CFR 84 for negative pressure air-purifying particulate respirators. These results showed penetration through the filter media of less than 0.03%, indicating that filter media were not a major source of aerosol leakage into the cab. The results suggest that the manufacturer should implement a quality control program to ensure that minimal aerosol penetration criteria into the cabs are met and an acceptable maintenance program exists to ensure compliance. Furthermore, the degradation of filter gasket material over time needs to be minimized to ensure that the environmental cabs continue to provide acceptable performance.

Biological Monitoring of Styrene in FRP‐Making Small Industries in Kumamoto, Japan—Winter‐Summer Difference and Effect of Protective Masks in Practical Working Conditions—

Biological Monitoring of Styrene in FRP‐Making Small Industries in Kumamoto, Japan—Winter‐Summer Difference and Effect of Protective Masks in Practical Working Conditions—: Tsukasa Inaoka, et al. Department of Public Health, Kumamoto University School of Medicine—Objective: Studies were carried out in Kumamoto, Japan to examine 1) the winter‐summer differences in the average individual exposure to styrene (8hr‐TWA) and to end‐shift‐urinary mandelic acid (MA in g/g Cr), 2) the possible seasonal difference in their relationship, and 3) the protective effect of a disposable particulate respirator containing charcoal fiber (called a “charcoal mask”) and a charcoal granule cartridge‐mask (called a “gas mask”) in the real working conditions. Methods: Approximately 100 male and female workers from about 10 small industries were subjected to the studies first in winter and second in summer. Individual exposure to styrene was monitored with a passive sampler during work time, and end‐shift‐urine was collected to determine urinary MA excretion. The content of their activities and the types of protective equipment were observed and recorded by the minute throughout the working day. Results: Neither individual exposure to styrene nor urinary MA excretion differed at the time of the study in both “no‐mask” and “gas mask” groups. The urinary MA excretion was related to individual exposure to styrene in both seasons, with the highest correlation coefficient in the “no‐mask” group. Since the regression slope for the “charcoal mask” group did not differ from that for “no‐mask” group, the “charcoal mask” was judged to have little protective effect in practical working conditions. From the difference in urinary MA values at 50 ppm (previous TLV‐TWA by ACGIH) of individual exposure to styrene in the two regressions for“no‐mask” and“gas mask” groups, 49% of styrene was protected against by the“gas mask” in winter, and 45% in summer. Conclusions: Despite different physical environmental conditions, individual exposure to styrene and urinary MA excretion did not differ by season in FRP‐making industries. A“gas mask” is more recommended than a“charcoal mask” when treating styrene, although their protective effects are decreased in practical working settings. It is basically necessary to give correct information on and free access to such protective equipment to styrene‐treating workers.

Factors Associated With the Personal Protective Equipments(PPEs) Wearing of Workers in Small Scale Industries

Objective: The aim of this study was to identify the factors associated with the wearing of Personal Protective Equipment (PPE) in small scale industries. Methods: In a cross-sectional study, the data were obtained from self-administered questionnaires, a special health examination and the industrial hygiene records. The study included 230 workers in small-scale industries (the print industry and automobile repair shops), which were provided with a subsidiary occupational health program funded by government in 1998. The authors used the Precede-Proceed model. Results: Among the subjects who were recommended to wear a PPE, 32.7% (35/107) wore the gas/vapor respirators, 43.9 % (101/230) wore the particulate respirators, and 44.3 % (102/230) wore hearing aids. Among them, 64.3 % (148/230) wore one of the above PPE. The wearing of PPE wearing was associated with knowledge (OR=2.34), the value of prevention (OR=3.46), social support (OR=2.78), the type of task (OR=2.18-4.47), and income level (OR=7.64). Conclusions: In small scale industries, the proportion workers wearing PPE was low. To increase this proportion, the reinforcing, enabling, and environmental factors as well as the predisposing factors need to be modified.

Letter to the Editor concerningValue of Limited Necropsy in HIV-positive Patients

The need to perform autopsies on and examine laboratory specimens from patients with hantavirus pulmonary syndrome (HPS) has raised questions about biosafety. Human illness associated with hantaviruses is usually the result of exposure to infectious aerosols from saliva or excreta of wild rodents. It is unclear whether or nor certain autopsy and laboratory procedures can also generate similar potentially infectious aerosols. As the biosafety information developed for the HPS agent is limited and the consequences of infection are serious we recommend a cautious approach. Autopsy prosectors should use N-95 particulate respirators as a minimum standard. If aerosols will be generated they should use N-100 particulate respirators or powered air purifying respirators with high-efficiency particulate air (HEPA) filters. Centrifugation and cytocentrifugation of blood or body fluid samples should be performed in bio-contained systems and these specimen containers should be opened in a class II biological safety cabinet.

Respiratory protection as a function of respirator fitting characteristics and fit-test accuracy.

The fitting characteristics of particulate respirators are no longer assessed in the National Institute for Occupational Safety and Health respirator certification program. It is important for respirator program administrators to understand the implications of that change and the additional burden it may impose. To address that issue, a typical respirator fit-testing program is analyzed using a mathematical model that describes the effectiveness of a fit-testing program as a function of the fitting characteristics of the respirator and the accuracy of the fittesting method. The model is used to estimate (1) the respirator assignment error, the percentage of respirator wearers mistakenly assigned an ill-fitting respirator; (2) the number of fit-test trials necessary to qualify a group of workers for respirator use; and (3) the number of workers who will fail the fit-test with any candidate respirator model and thereby fail to qualify for respirator use. Using data from previous studies, the model predicts respirator assignment errors ranging from 0 to 20%, depending on the fitting characteristics of the respirator models selected and the fit-testing method used. This analysis indicates that when respirators do not necessarily have good fitting characteristics, respirator program administrators should exercise increased care in the selection of respirator models and increased care in fit-testing. Also presented are ways to assess the fitting characteristics of candidate respirator models by monitoring the first-time fit-testing results. The model demonstrates that significant public health and economic benefits can result when only respirators having good fitting characteristics are purchased and respirators are assigned to workers using highly accurate fit-testing methods.

Electrostatic respirator filter media: filter efficiency and most penetrating particle size effects.

New electrostatic filter media has been developed for use in 42 CFR 84 negative pressure particulate respirator filters. This respirator filter media was not available for evaluation prior to the change from 30 CFR 11 to 42 CFR 84. Thus, characterization of this filter media is warranted. In this study, the new 42 CFR 84 electrostatic respirator filters were investigated with respect to filter penetration and most penetrating particle size. Three different models of N95 filters, along with one model each of the N99, R95, and P100 class filters were used in this study. First, three of each filter were loaded with a sodium chloride (NaCl) aerosol, and three of each filter were loaded with a dioctyl phthalate (DOP) aerosol to obtain normal background penetration results for each filter. Then, two new filters of each type were dipped in isopropanol for 15 seconds and allowed to dry. This isopropanol dip should reduce or eliminate any electrostatic charge on the fibers of each filter, as reported in the technical literature. These dipped filters, along with controls of each filter type, were tested on a TSI 8160 filter tester to determine the most penetrating particle size. These same filters were then tested against a NaCl aerosol to get final penetration values. Electret filters rely heavily on their electrostatic charge to provide adequate filter efficiencies, and correlations between penetration and a filter's electrostatic characteristics are found in the technical literature. In all six of the filter models tested, filter penetration values increased considerably and the most penetrating particle size noticeably shifted toward larger particles. These results are important in better understanding how these new filter materials perform under various conditions, and they indicate the need for additional research to define environmental conditions that may affect electrostatic filter efficiency.

Respirator leakage in the pharmaceutical industry of Northwest England

Field qualitative fit tests were conducted at 10 separate companies in the Northwest of England to determine the proportion of leaking respirators in a cross-section of pharmaceutical manufacturing industries. The 3 M FT-10 Qualitative Fit Test Apparatus was used to test a total of 211 half-face particulate respirator wearers. Participants wore their own respirators and were asked to don them as they would normally. In all cases, no specific intervention had occurred prior to testing. Results indicated a failure rate of 69% (of the 211 subjects tested, 145 respirators were leaking). Successful results were not associated with the frequency of use (p = 0.71) or years of experience wearing respirators (p = 0.59). Similarly, successful results were not associated with respirator training in the current job (p = 0.38) or training in previous jobs (p = 0.49). Leakage was not consistent across the 10 companies, with two companies exhibiting a 100% failure rate while another company had 26 successful tests in 50 wearers (52% pass rate). Only 35 of the 211 participants performed a negative pressure test. Of these, 80% successfully passed the test, which was significantly greater than the 22% pass rate among those who had not performed the pressure test (p < 0.001).

Respirator leakage in the pharmaceutical industry of Northwest England

Field qualitative fit tests were conducted at 10 separate companies in the Northwest of England to determine the proportion of leaking respirators in a cross-section of pharmaceutical manufacturing industries. The 3 M FT-10 Qualitative Fit Test Apparatus was used to test a total of 211 half-face particulate respirator wearers. Participants wore their own respirators and were asked to don them as they would normally. In all cases, no specific intervention had occurred prior to testing.Results indicated a failure rate of 69% (of the 211 subjects tested, 145 respirators were leaking). Successful results were not associated with the frequency of use (p=0.71) or years of experience wearing respirators (p=0.59). Similarly, successful results were not associated with respirator training in the current job (p=0.38) or training in previous jobs (p=0.49). Leakage was not consistent across the 10 companies, with two companies exhibiting a 100% failure rate while another company had 26 successful tests in 50 wearers (52% pass rate). Only 35 of the 211 participants performed a negative pressure test. Of these, 80% successfully passed the test, which was significantly greater than the 22% pass rate among those who had not performed the pressure test (p<0.001).

Tuberculosis exposure risk in emergency medicine residents.

To assess purified protein derivative (PPD) test surveillance and respiratory protection practices of emergency medicine (EM) residents, along with the prevalence of PPD test conversion and the development of active tuberculosis (TB) in EM residents. The study instrument was an anonymous, self-reporting, multiple-choice survey administered to U.S. and Canadian EM residents. It was distributed for voluntary completion in conjunction with the American Board of Emergency Medicine's annual in-service examination, which was administered February 25, 1998. A total of 89.3% (n = 2,985) of residents eligible to complete the survey completed at least part of it. The majority of residents are PPD-tested once a year. The prevalence of PPD test conversions in EM residents was between 1.4% (36/2,575) and 2.0% (52/2,575). Of the residents who PPD test-converted, the ED was most often the perceived area of TB source exposure (n = 15). Two residents (0.08%) reported having developed active TB, including chest radiographic findings or clinical infection, which equals a 0.14% (95% CI = 0.005 to 0.31) risk of developing active TB over a three-year residency. Half of all the residents do not routinely wear National Institute for Occupational Safety and Health (NIOSH)-approved particulate filtration respirator (PFR) masks in patient encounters at risk for TB exposure. While more than a third of EM residents have not undergone fit testing for a NIOSH-approved PFR mask, the lack of routine easy availability of such masks is the most common reason they are not routinely worn by EM residents during at-risk encounters for TB transmission. Most surveillance PPD testing of EM residents is performed at intervals recommended by the CDC. TB control programs at institutions sponsoring EM residencies need to improve both compliance with PFR mask fit testing by EM residents and availability of approved PFR masks in appropriate areas of the ED. Despite poor compliance with personal respiratory protection in ED patient encounters at risk for TB transmission, the risk of an EM resident's developing active TB over a three-year residency is low.

Simulated workplace performance of N95 respirators.

During July 1995 the National Institute for Occupational Safety and Health (NIOSH) began to certify nine new classes of particulate respirators. To determine the level of performance of these respirators, NIOSH researchers conducted a study to (1) measure the simulated workplace performance of 21 N95 respirator models, (2) determine whether fit-testing affected the performance, and (3) investigate the effect of varying fit-test pass/fail criteria on respirator performance. The performance of each respirator model was measured by conducting 100 total penetration tests. The performance of each respirator model was then estimated by determining the 95th percentile of the total penetration through the respirator (i.e., 95% of wearers of that respirator can expect to have a total penetration value below the 95th percentile penetration value). The 95th percentile of total penetrations for each respirator without fit-testing ranged from 6 to 88%. The 95th percentile of total penetrations for all the respirators combined was 33%, which exceeds the amount of total penetration (10%) normally expected of a half-mask respirator. When a surrogate fit test (1% criterion) was applied to the data, the 95th percentile of total penetrations for each respirator decreased to 1 to 16%. The 95th percentile of total penetrations for all the respirators combined was only 4%. Therefore, fit-testing of N95 respirators is necessary to ensure that the user receives the expected level of protection. The study also found that respirator performance was dependent on the value of the pass/fail criterion used in the surrogate fit-test.

Aerosol Loading Performance of Electret Filter Media

In this study various types of flat sheet electret filter media including tribocharged polypropylene/acrylic, corona charged polypropylene, fibrillated electret film, and new advanced electret media have been compared with mechanical filter media (fiber glass) using aerosol filtration tests designed for particulate respirators. The number of layers, and thus the total mass and pressure drop, of the media were varied while the filter area exposed to the aerosol and the aerosol flow rate was held constant (constant face velocity). Tests included challenges with sodium chloride and dioctyl phthalate (DOP) aerosols per NIOSH 42 CFR 84 specifications for particulate respirator certification. Initial filtration efficiency and pressure drop and the same during loading were determined. Results revealed significant differences in filtration performance and loading behavior among the various media. It is concluded that respirators can be designed for all nine 42 CFR 84 classes using electret filter media without sacrificing low pressure drop, light weight, or user comfort.

Aerosol Loading Performance of Electret Filter Media

In this study various types of flat sheet electret filter media including tribocharged polypropylene/acrylic, corona charged polypropylene, fibrillated electret film, and new advanced electret media have been compared with mechanical filter media (fiber glass) using aerosol filtration tests designed for particulate respirators. The number of layers, and thus the total mass and pressure drop, of the media were varied while the filter area exposed to the aerosol and the aerosol flow rate was held constant (constant face velocity). Tests included challenges with sodium chloride and dioctyl phthalate (DOP) aerosols per NIOSH 42 CFR 84 specifications for particulate respirator certification. Initial filtration efficiency and pressure drop and the same during loading were determined. Results revealed significant differences in filtration performance and loading behavior among the various media. It is concluded that respirators can be designed for all nine 42 CFR 84 classes using electret filter media without sacrificing low pressure drop, light weight, or user comfort.

Method for measuring the spatial variability of aerosol penetration through respirator filters.

Fibrous filter media are widely used in respirators to remove airborne particulate matter from the inhaled airflow of workers. The N95 half-mask particulate respirator appears to be the most frequently used respirator under the new NIOSH regulation, 42 CFR 84. Considerable spatial variability in light penetration through the fibrous filter medium of an N95 respirator can be seen by visual observation when it is held to the light. This variability is due to the way in which the fibers are manufactured and laid down to form the filter medium. Similar spatial variability is expected in the aerosol penetration through the filters. Therefore, a test method has been developed for measuring the spatial variability in aerosol penetration. The main components of this method are an aerosol generator, a filter test stand with a movable sampling inlet, an aerosol size spectrometer, and an aerosol photometer. Measurements with the filter media of N95 respirators, tested at average filtration velocities corresponding to light, moderate, and heavy work loads, have shown spatial variations in aerosol penetration in excess of 100% relative to the average aerosol penetration for the entire respirator. N95 respirators are required to be at least 95% efficient (i.e., less than 5% penetrating) at the most penetrating particle size, when tested at 85 L/min. Tests with the new method have shown that the aerosol penetration of the most penetrating particles of about 0.1 micron diameter may locally be higher than 5%, while the average aerosol penetration of 0.1 micron particles is less than 5%.

Performance of N95 Respirators: Filtration Efficiency for Airborne Microbial and Inert Particles

In 1995 the National Institute for Occupational Safety and Health issued new regulations for nonpowered particulate respirators (42 CFR Part 84). A new filter certification system also was created. Among the new particulate respirators that have entered the market, the N95 respirator is the most commonly used in industrial and health care environments. The filtration efficiencies of unloaded N95 particulate respirators have been compared with those of dust/mist (DM) and dust/fume/mist (DFM) respirators certified under the former regulations (30 CFR Part 11). Through laboratory tests with NaCl certification aerosols and measurements with particle-size spectrometers, N95 respirators were found to have higher filtration efficiencies than DM and DFM respirators and noncertified surgical masks. N95 respirators made by different companies were found to have different filtration efficiencies for the most penetrating particle size (0.1 to 0.3 µm), but all were at least 95% efficient at that size for NaCl particles. Above the most penetrating particle size the filtration efficiency increases with size; it reaches approximately 99.5% or higher at about 0.75 µm. Tests with bacteria of size and shape similar to Mycobacterium tuberculosis also showed filtration efficiencies of 99.5% or higher. Experimental data were used to calculate the aerosol mass concentrations inside the respirator when worn in representative work environments. The penetrated mass fractions, in the absence of face leakage, ranged from 0.02% for large particle distributions to 1.8% for submicrometer-size welding fumes. Thus, N95 respirators provide excellent protection against airborne particles when there is a good face seal.

Playing it safe with a particulate respirator.

Playing it safe with a particulate respirator.

The Cost-effectiveness of Preventing Tuberculosis in Physicians Using Tuberculin Skin Testing or a Hypothetical Vaccine

Tuberculin skin testing using the purified protein derivative is recommended as part of a tuberculosis control program for health care workers. However, compliance with skin testing programs has been poor and their cost-effectiveness is unknown. A Markov-based decision analysis was performed to determine the cost-effectiveness of tuberculin skin testing over the entire lifetimes of physicians who are now in medical school. Assumptions were deliberately chosen to present a conservative estimate of cost-effectiveness. Indirect costs were not included. Annual testing cost $29,000 per life-year saved and $39,000 per case of pulmonary tuberculosis prevented. In contrast, particulate respirators have been shown to cost millions of dollars per case prevented. Skin testing every 6 months was cost-effective in a subpopulation at high risk of infection (> or = 1.8-fold). During their entire lifetimes, physicians now in medical school can expect to avert 137 cases of pulmonary tuberculosis, prevent 7 tuberculosis deaths, and save 182 life-years because of skin testing programs. Improved compliance with annual skin testing and prophylactic isoniazid could more than triple this benefit. If available, a moderately effective vaccine would be even more cost-effective than tuberculin skin testing programs. Tuberculin skin testing is cost-effective and should be an integral part of any tuberculosis control program. Vaccination may one day be a feasible and cost-effective alternative to skin testing programs.