Negative-pressure Respirators Research Articles

Aerosolized Particle Reduction: A Novel Cadaveric Model and a Negative Airway Pressure Respirator (NAPR) System to Protect Health Care Workers From COVID-19.

ObjectivesThis study aimed to identify escape of small-particle aerosols from a variety of masks using simulated breathing conditions. This study also aimed to evaluate the efficacy of a negative-pressure environment around the face in preventing the escape of small aerosolized particles.Study DesignThis study is an evaluation study with specific methodology described below.SettingThis study was performed in our institution’s fresh tissue laboratory.Subjects and MethodsA fixed cadaver head was placed in a controlled environment with a black background, and small-particle aerosols were created using joss incense sticks (mass-median aerosol diameter of 0.28 µ). Smoke was passed through the cadaver head, and images were taken with a high-resolution camera in a standardized manner. Digital image processing was used to calculate relative amounts of small-particle escape from a variety of masks, including a standard surgical mask, a modified Ambu mask, and our negative airway pressure respirator (NAPR).ResultsSignificant amounts of aerosolized particles escaped during the trials with no mask, a standard surgical mask, and the NAPR without suction. When suction was applied to the NAPR, creating a negative-pressure system, no particle escape was noted.ConclusionWe present a new and effective method for the study of small-particle aerosols as a step toward better understanding the spread of these particles and the transmission of coronavirus disease 2019. We also present the concept of an NAPR to better protect health care workers from aerosols generated from the upper and lower airways.

Respiratory Protection Provided by Negative Pressure Half Mask Filtering Respirators in Coal Mines

Two studies were conducted in the coal mines to evaluate worker exposures to a dust, and the effectiveness of air-purifying negative-pressure half mask respirators and was found that miners’ protection were insufficient. An elastomeric and filtering half-mask negative pressure respirators with (mid-efficiency) filters P2 (FFP2) were studied. Measurements of total dust concentrations in the in-mask and outer air were conducted simultaneously. Not identical sampling system led to an underestimation of the actual total inside dust concentration in the first study. The results have been corrected to reduce the systematic error. The inside total dust concentrations Ci exceeded national Permissible Exposure Limit (PEL) in most cases in both studies; in first GM Ci=24.7 mg/m3; in second 8.6 mg/m3. Protection factors were: from 2.9 to 6.9 in first study; and from 5.6 to 34 in second. Low efficiency of respirators can be caused by its non-continuous usage. High risk of miners’ occupational diseases should be reduced by decreasing the dust concentration in the breathing zone. It is advisable to check the possibility of improving respiratory protection of miners by powered air-purifying respirators.

Influence of facial hair length, coarseness, and areal density on seal leakage of a tight-fitting half-face respirator

ABSTRACTBackground: OSHA regulations state that an employer shall not permit tight-fitting respirators to be worn by employees who have facial hair that comes between the skin and facepiece seal. Studies have shown that facial hair in the face seal zone can increase penetration and decrease the fit factor (FF), although the relationship between the amount and characteristics of facial hair and the increase in penetration is not well quantified. This article examines the influence of facial hair length, areal density, and coarseness on FF for one model of half-face elastomeric negative-pressure air purifying respirator.Approach: Quantitative fit tests (QNFT) were performed on 19 subjects with beards initially 0.500-in long and subsequently trimmed to 0.250, 0.125, and 0.063 in, then after a razor shave. Three fit tests were performed at each of the 5 lengths, for 285 total tests. The average diameter and areal density of cheek and chin hair were measured. Penetration was modeled as a function of hair length category, beard areal density, and hair coarseness.Results: FF decreased with beard length, especially beyond 0.125 in. However, passing FF scores were achieved on all tests by all subjects at the smooth shave and 0.063 in conditions, and 98% of tests were passed at 0.125 in; seven subjects passed all tests at all conditions. Chin and cheek areal densities were significantly different and were only weakly correlated. Beard hair diameters were normally distributed across subjects (mean 76 µm, standard deviation 7.4 µm). Beard length and areal density, but not coarseness, were statistically significant predictors of fit using an arcsine transformed penetration model. FF decreased with increasing beard length, especially beyond 0.125 in, although FF with a “stubble” beard did not differ significantly from a smooth shave. FF also decreased with increasing areal beard hair density.Conclusion: Beard length and areal density negatively influence FF. However, tight-fitting half-face negative-pressure respirator fit tests can achieve adequate fit factor scores even with substantial facial hair in the face seal area.

Manual positive pressure ventilation and the Copenhagen poliomyelitis epidemic 1952: An attempt at setting the record straight.

A short recapitulationis necessary, however, before I attempt to assess themerits and demerits of the physicians involved inthe treatment of polio patients during the severeCopenhagen epidemic.During the first 4 weeks of the epidemic, 27 of 31patients with bulbar-spinal paralysis had died. Withhis back against the wall, the head of the Depart-ment of Communicable Diseases, professor HenryCai Alexander Lassen, on the suggestion and urgeof his senior registrar, Mogens Bjorneboe, reluc-tantly summoned a freelance anasthetist – BjornIbsen. Ibsen had no experience with polio patients,but he recognized the clinical picture as one domi-nated by respiratory insufficiency with carbondioxide retention – despite the use of negative pres-sure respirators. His advice was to tracheotomizethe patients and use intermittent positive pressureventilation (IPPV) afterwards. He demonstrated thefeasibility of his method on a 12-yr-old girl

Heat stress evaluation of two-layer chemical demilitarization ensembles with a full face negative pressure respirator.

The purpose of this study was to examine the heat stress effects of three protective clothing ensembles: (1) protective apron over cloth coveralls including full face negative pressure respirator (APRON); (2) the apron over cloth coveralls with respirator plus protective pants (APRON+PANTS); and (3) protective coveralls over cloth coveralls with respirator (PROTECTIVE COVERALLS). In addition, there was a no-respirator ensemble (PROTECTIVE COVERALLS-noR), and WORK CLOTHES as a reference ensemble. Four acclimatized male participants completed a full set of five trials, and two of the participants repeated the full set. The progressive heat stress protocol was used to find the critical WBGT (WBGTcrit) and apparent total evaporative resistance (Re,T,a) at the upper limit of thermal equilibrium. The results (WBGTcrit [°C-WBGT] and Re,T,a [kPa m2 W−1]) were WORK CLOTHES (35.5, 0.0115), APRON (31.6, 0.0179), APRON+PANTS (27.7, 0.0244), PROTECTIVE COVERALLS (25.9, 0.0290), and PROTECTIVE COVERALLS-noR (26.2, 0.0296). There were significant differences among the ensembles. Supporting previous studies, there was little evidence to suggest that the respirator contributed to heat stress.

The effects of wearing respirators on human fine motor, visual, and cognitive performance

When selecting a respirator, it is important to understand how employees' motor, visual and cognitive abilities are impacted by the personal protective equipment. This study compares dust, powered-air-purifying and full-face, negative-pressure respirators. Thirty participants performed three varied tasks. Each participant performed each task without a respirator and while wearing the three respirator types. The tasks included a hand tool dexterity test, the Motor-Free Visual Perception Test and the Serial Sevens Test to evaluate fine motor, visual and cognitive performance, respectively. The time required for task completion and the errors made were measured. Analysis showed no significant effect due to respirator use on the task completion time. A significant increase was found in the error rate when participants performed the cognitive test wearing the full-face, negative-pressure respirator. Participants had varying respirator preferences. They indicated a potential for full-face, negative-pressure respirators to negatively affect jobs demanding high cognitive skills such as problem solving and decision-making. Practitioner summary: while respirators are life-saving personal protective equipment (PPE), they can unintentionally reduce human performance, especially if job characteristics are not considered during PPE selection. An experiment was conducted to compare three respirators (dust respirator, powered-air-purifying respirators and full-face respirator) for varying task types. The full-face respirator was found to affect human cognitive performance negatively.

A comparison of different types of hazardous material respirators available to anesthesiologists

Despite anesthesiology personnel involvement in initial treatment of patients exposed to potentially lethal agents, less than 40 percent of US anesthesiology training programs conduct training to manage these patients.(1) No previous studies have evaluated performance of anesthesiologists wearing protective gear. The authors compared the performance of anesthesiologists intubating a high-fidelity mannequin while wearing either a powered air-purifying respirator (PAPR) or a negative pressure respirator (NPR). Twenty participants practiced intubations on a high-fidelity simulator until comfortable. Each subject performed 10 repetitions, initially without any gear, then while wearing a protective suit, gloves, and respirator. The order of gear use was randomized and all subjects used both devices. Time for task completion were recorded, and at the end of the trial, subjects were asked to rate their comfort with the equipment. After controlling for other variables, overall statistically slower total performance times were observed with use of the PAPR when compared to the control arm and use of the NPR (p 5 0.01 and p < 0.007, respectively). Of the total 90 intubations, only one proved to be esophageal and initially undetected. The use of an NPR or PAPR does not preclude an anesthesiologist from successfully intubating, but practice is necessary. The slightly better performance with the NPR is weighed against the improved comfort of the PAPR and the fact that PAPR users could wear eyeglasses. Neither type of gear allowed the users to auscultate the lung fields to confirm correct endotracheal tube placement.

Expanding ICU facilities in an epidemic: recommendations based on experience from the SARS epidemic in Hong Kong and Singapore

Epidemics have the potential to severely strain intensive care resources and may require an increase in intensive care capability. Few intensivists have direct experience of rapidly expanding intensive care services in response to an epidemic. This contribution presents the recommendations of an expert group from Hong Kong and Singapore who had direct experience of expanding intensive care services in response to the epidemic of severe acute respiratory syndrome. These recommendations cover training, infection control, staffing, communication and ethical issues. The issue of what equipment to purchase is not addressed. Early preparations should include fit testing of negative pressure respirators, training of reserve staff, sourcing of material for physical modifications to the ICU, development of infection control policies and training programmes, and discussion of triage and quarantine issues.

Efficacy of the Combined Use of Negative Pressure on the Lower Part of the Body and Negative-Pressure Respiration under Simulated Microgravity

The efficacies of the standard procedure for application of negative pressure on the lower part of the body (NPLB) and a combination of NPLB and negative-pressure respiration (NPR) during a simulated last stage of a spaceflight under conditions of antiorthostatic hypokinesia (ANOH, –6°) and isolation for 7 days have been compared in the course of three series of tests involving six volunteers in an EU-100 pressurized chamber. After the end of the 7-day ANOH and isolation, episodes of orthostatic disorders were observed in all six subjects in the first series of tests (the control series) and in four subjects in the second series (NPLB). In the third series (NPLB + NPR), orthostatic disorders, if any, were slight. Two main conclusions have been made. First, ANOH combined with isolation in a small chamber may be used to simulate the effects of the combined factors of spaceflight on humans in order to obtain model gravitational circulatory disorders. Second, the combined use of NPLB + NPR under these conditions may be effective for the prevention of orthostatic circulatory disorders in humans.

The effects of strapped spectacles on the fit factors of three manufactured brands of full facepiece negative pressure respirators

A study was conducted to determine the effects of strapped spectacles on the fit factors obtained during quantitative fit testing on three different brands of full facepiece negative pressure respirators. The three brands of respirators were evaluated with and without strapped spectacles worn by the test subjects. A total of 180 quantitative fit testing trials were conducted on ten male test subjects. For each test subject, three quantitative fit testing trials were performed with each brand of respirator with and without the spectacles. The average of the fit testing trials for each subject with each respirator was used for statistical analysis. The results demonstrated that the fit factor values were significantly lower during use of the spectacles (p<0.05). The estimated percentage of test subjects who failed the American National Standards Institute pass/fail criteria for quantitative fit testing (1000) increased by 15–36% when spectacles were worn.

The effects of strapped spectacles on the fit factors of three manufactured brands of full facepiece negative pressure respirators

A study was conducted to determine the effects of strapped spectacles on the fit factors obtained during quantitative fit testing on three different brands of full facepiece negative pressure respirators. The three brands of respirators were evaluated with and without strapped spectacles worn by the test subjects. A total of 180 quantitative fit testing trials were conducted on ten male test subjects. For each test subject, three quantitative fit testing trials were performed with each brand of respirator with and without the spectacles. The average of the fit testing trials for each subject with each respirator was used for statistical analysis. The results demonstrated that the fit factor values were significantly lower during use of the spectacles (p<0.05). The estimated percentage of test subjects who failed the American National Standards Institute pass/fail criteria for quantitative fit testing (1000) increased by 15–36% when spectacles were worn.

Aerosol Penetration Behavior of Respirator Valves

Exhalation and inhalation valves from half-facepiece negative pressure respirators were evaluated for leakage during an 8-hour cyclic breathing test period using two work rates (415 and 622 kg-m/min) and two particle sizes (0.3 and 0.8 µm). Three different models (manufacturers) of exhalation valves were tested, with two lots for each model. Exhalation valve leakage ranged from 0.0 to 0.03%; no failure of exhalation valves occurred. No differences in lot or manufacturer were found. Differences in particle size did not lead to differences in penetration at the lower work rate; at the higher work rate 0.3-µm particles were less penetrating than 0.8-µm particles (0.03 versus 0.06%). When tested for air leakage at a pressure of 2.54 cm H2O, following the National Institute for Occupational Safety and Health certification method, exhalation valves exhibited no leakage either before or after the experiments. Inhalation valves averaged 20% leakage for all experiments; 0.3-µm particles were again less penetrating (13%) than 0.8-µm particles (27%). No inhalation valve failure occurred. No differences in lot (within manufacturer) were found; there were, however, significant differences in particle penetration among the three manufacturers' inhalation valves. Airflow leakage through the inhalation valves did not change during the experimental period, but differed among the three manufacturers. Measurements using airflow leakage and particle penetration produced the same ranking for the three manufacturers' inhalation valves.

Efficacy of Selected Respiratory Protective Equipment Challenged with Bacillus subtilis subsp. niger

The efficacy of powered air-purifying respirators, surgical masks, dust/mist respirators, and high-efficiency respirators were tested with a biological aerosol under simulated breathing conditions. Protective ability ranged from 67 to 99.95%. The majority of penetration in negative-pressure respirators occurred at the face-mask interface rather than through the filter material.

Estimated Workplace Protection Factors for Positive-pressure Self-Contained Breathing Apparatus

An analytical model is presented that estimates the distribution of workplace protection factor (WPF) values for positive-pressure respirators. Input for the model is (1) the instantaneous facepiece pressure measured as a function of time and (2) the distribution of WPF values for a negative-pressure version of the respirator. As an example application, the model was applied to 57 measurements of facepiece pressure made in a previous National Institute for Occupational Safety and Health study called “Firesmoke.” That study involved professional firefighters wearing positive-pressure self-contained breathing apparatus (SCBA). During Firesmoke, there were four donnings in which facepiece pressure momentarily went negative one or more times during use. The purpose of the effort described here was to assess the significance of these momentary, negative excursions in facepiece pressure. To that end, an analytical model was developed that estimates the ratio of the mass of contaminant that enters the facepiece during these negative excursions to that which would be expected to enter a negative-pressure respirator utilizing the same facepiece. Thus, the performance of a positive-pressure SCBA can be determined relative to the performance of a negative-pressure respirator with the same facepiece—either a negative-pressure SCBA or a negative pressure air-purifying respirator. The NIOSH-assigned protection factor (APF) for a negative-pressure full facepiece is 50; the APF for a positive-pressure SCBA is 10 000. The results of the application of this analytical model are consistent with the current NIOSH APF for a positive-pressure SCBA.

Estimated workplace protection factors for positive-pressure self-contained breathing apparatus.

An analytical model is presented that estimates the distribution of workplace protection factor (WPF) values for positive-pressure respirators. Input for the model is (1) the instantaneous facepiece pressure measured as a function of time and (2) the distribution of WPF values for a negative-pressure version of the respirator. As an example application, the model was applied to 57 measurements of facepiece pressure made in a previous National Institute for Occupational Safety and Health study called "Firesmoke." That study involved professional firefighters wearing positive-pressure self-contained breathing apparatus (SCBA). During Firesmoke, there were four donnings in which facepiece pressure momentarily went negative one or more times during use. The purpose of the effort described here was to assess the significance of these momentary, negative excursions in facepiece pressure. To that end, an analytical model was developed that estimates the ratio of the mass of contaminant that enters the facepiece during these negative excursions to that which would be expected to enter a negative-pressure respirator utilizing the same facepiece. Thus, the performance of a positive-pressure SCBA can be determined relative to the performance of a negative-pressure respirator with the same facepiece--either a negative-pressure SCBA or a negative pressure air-purifying respirator. The NIOSH-assigned protection factor (APF) for a negative-pressure full facepiece is 50; the APF for a positive-pressure SCBA is 10,000. The results of the application of this analytical model are consistent with the current NIOSH APF for a positive-pressure SCBA.

Evaluation of new in-facepiece sampling procedures for full and half facepieces.

Precision and bias were determined on five different methods of conducting in-facepiece sampling. In-board penetration occurred through fixed, circular, leak geometries positioned at different areas on the face-seal of full and half facepiece negative-pressure respirators. The sampling procedures evaluated in the study were: (1) a continuous, low sampling rate, flush on the respirator, mid nose-mouth probing (CLF) procedure; (2) a continuous, high sampling rate, deep front-of-mouth probing (CHD) procedure; (3) a pulsed exhalation, deep front-of-mouth probing (PED) procedure; (4) an exhalation value discharge (EVD) procedure; and (5) a pulsed inhalation, deep front-of-mouth, probing (PID) procedure. The CLF procedure represents a recommended in-facepiece sampling procedure in the United States. Evaluations were done on populations of nine full facepiece respirators and five half facepieces. The full facepieces were not equipped with nose cups. The average sampling biases on the full facepieces were: (1) CLF procedure, -21%; (2) CHD procedure, -3%; (3) PED procedure, 0.7%; (4) EVD procedure, -14%; and (5) PID procedure, -12.3%. On the five half facepiece respirators the average sampling biases were: (1) CLF procedure, -26%; (2) CHD procedure, -13%; (3) PED procedure, -4%; (4) EVD procedure, -2%; and (5) PID procedure, -24%. The bias observed with each method was found to be affected, to some extent, by the location of the face-seal penetration.

A Comparison of Controlled Negative Pressure and Aerosol Quantitative respirator Fit Test Systems by Using Human Subjects

A Comparison of Controlled Negative Pressure and Aerosol Quantitative respirator Fit Test Systems by Using Human Subjects

Workplace Protection Factor Evaluation of Respiratory Protective Equipment in a Primary Aluminum Smelter

Abstract A study was performed at the Arvida Works of Alcan to determine the suitability of a helmeted Powered Air Purifying Respirator (PAPR) in a primary aluminum smelting plant using the horizontal stud Söderberg process. Participants in the test program were worker volunteers drawn from various jobs performed by the anode crews. The research protocol was developed to complement the work methodologies used by Alcan with as little change as possible in their work schedules. Half the crews wore dual cartridge half-mask negative pressure respirators and the other half wore helmeted PAPRs. The dual cartridge half-mask negative pressure respirators were equipped with organic vapors/acid gas cartridges and dust/mist/fumes or dust/mist prefilters; the PAPRs were equipped with organic vapors/HEPA filter cartridges. B(a)P was selected as the measurable contaminant. Under the conditions of this study—that is, strict adherence to the test protocol—we found that 95 percent of the Workplace Protection Factors (also called the 5th percentile) were above 275 for helmeted PAPRs and above 9 for dual cartridge half-mask negative pressure respirators. However, if results under less than ideal worker compliance conditions brought Workplace Protection Factors down by a factor of 10, then the helmeted PAPRs would still provide adequate respiratory protection in this study. The results indicate that the B(a)P concentrations expressed as time-weighted average exposure were significantly less than 0.5 μg/m3 for both types of respirators. Gaboury, A.; Burd, D.H.; Friar, R.S.: Workplace Protection Factor Evaluation of Respiratory Protective Equipment in a Primary Aluminum Smelter. Appl. Occup. Environ. Hyg. 8(1):19-25; 1993.

A Comparison of Controlled Negative Pressure and Aerosol Quantitative Respirator Fit Test Systems by Using Fixed Leaks

A Comparison of Controlled Negative Pressure and Aerosol Quantitative Respirator Fit Test Systems by Using Fixed Leaks

Ventricular External Constraint by the Lung and Pericardium during Positive End-expiratory Pressure

We studied intra- and extrapericardial surface pressures (Ppe and Pex) over the left ventricle with air-filled flat balloons in six dogs under different levels of positive end-expiratory pressure (PEEP) and left ventricular end-diastolic pressure. Pex reflected lung constraint and the transpericardial pressure (Ppe-Pex) reflected the elastic recoil of the pericardium (pericardial constraint). Under baseline plasma volume conditions with a PEEP of 0 cm H2O, Ppe was 2.4 +/- 0.2 (SEM) mm Hg and Pex was 0.2 +/- 0.1 mm Hg; that is, 91% of Ppe was contributed by the transpericardial pressure. With incremental increases in PEEP, Pex increased and approach Ppe with a decrease in the transpericardial pressure (p less than 0.01). With a PEEP of 20 cm H2O, Ppe was 5.3 +/- 0.1 mm Hg and Pex was 5.0 +/- 0.2 mm Hg; that is, less than 5% of Ppe was contributed by the transpericardial pressure. Under plasma volume-loaded conditions with an increase in PEEP to 20 cm H2O, Pex increased but remained lower than Ppe, with a substantial contribution of transpericardial pressure still present (19%). These results suggest that lung constraint alone can substantially constrain the left ventricle and that the influence of lung constraint, rather than pericardial constraint, may be progressively important with an elevated lung volume produced by either positive- or negative-pressure respiration.