Performance Evaluation of Powered Air-Purifying Respirators

1659 

Student Poster 

C HSU¹, S HUANG¹, C LIN¹, C CHEN¹

¹National Taiwan University, Taipei, Taiwan

CHAO-HAO HSU  
National Taiwan University

SHENG-HSIU HUANG  
National Taiwan University

CHIH-WEI LIN  
National Taiwan University

CHIH-CHIEN CHEN  
National Taiwan University

Powered air-purifying respirators (PAPRs) are equipped with a battery powered blower to push atmospheric air through a filter into the respirator cavity. With the blower, wearers can use less effort to breath than wearing negative-pressure respirators like N95, so that extend the work performance time. In general, constant-flow PAPRs, is meant that the supply air generated by blower is fixed, is more common to use. Recently, a set of pressure demand auto-feedback PAPRs is on the market. The pressure demand PAPRs can supply different flow with the demand of the wearers' breath in order to maintain the positive pressure inside the respirator. However, In order to have the pressure inside respirator become positive, the blower must be big enough to supply sufficient airflow to respirators. With the big blower, wearers may feel uncomfortable for long-term working. Moreover, if the airflow supplied into the respirators is too large in normal breathing situation, the excessive pressure would cause the respiratory burden.

Many researches recruit volunteers to use PAPRs in different breathing situation, and evaluate the effectiveness of PAPRs with the feelings of the subjects, however, they are lack of the systematic performance evaluation of PAPRs with the pressure and the flow rate, especially for the pressure demand auto-feedback PAPRs. This study aimed to evaluate the performance characteristics of three constant-flow PAPRs and a set of pressure demand auto-feedback PAPRs. With the experimental system set-up for measuring the pressure inside the respirator and flow rate generated by blower, we could realize the mechanism of the pressure demand PAPRs. In addition, we could also use the minimum pressure inside the respirators to realize the limit of type of PAPRs used in the study. With the pressure and the comfort, we could make suggestion to choose the suitable PAPRs in different breathing situation. Most important, With the problem in the commercial PAPRs, A new PAPRs could be developed, and to improve the pressure feedback system to enhance the comfort level of PAPRs.

Three brands of constant-flow PAPRs and a set of pressure demand auto-feedback PAPRs were evaluated in the study. The PAPRs was donned on a head-form, and connected to a breathing simulator with adjustable tidal volume (0.5-3 L) and breathing frequency (15-50 time/min) in order to simulate different breathing conditions(7.5 – 105 L/min). A pressure transducer was used to monitor the pressure drop inside respirator. The signal of pressure drop was presented as voltage, and then output to a data acquisition system. The pressure transducer was calibrated with an inclined manometer, a T-connector was used to apply the same pressure simultaneously to pressure transducer and inclined manometer. A calibration curve was made of the electrical voltage related to the transducer pressure and value of inclined manometer. The measuring rate of pressure transducer was set as 0.1 seconds to synchronize with breathing pattern. The flow rate generated by the blower was measured by a thermal mass flow meter; A acrylic chamber connected with a circle-tube was built to cover the filter component, and silicone was coated over the chamber in order to prevent from leaking during measurement. Then, a thermal mass flow meter was set on the tube to detect the air velocity generated by the operating of PAPRs blower. Thermal mass flow meter was calibrated with a wet gas meter in order to ensure the accuracy of air velocity. The measuring rate of the flow meter was the same as the pressure transducer. The measuring time of the pressure and flow rate was least 90 seconds in order to know completely performance of each type PAPRs.

In pressure demand auto-feedback PAPRs, The blower first supply a greater flow in order to make sure that pressure must be positive in any breathing condition. When the breathing flow is over 50 L/min, supply air flow would increased apparently in order to maintain pressure positive. Then, the steady flow generated by the blower after system identification was increased with the decreasing pressure when inhalation, indicating that feedback system of pressure demand PAPRs is functioning.
Make a comparison between four type PAPRs in our study, the pressure inside the respirator maintain 6-8 mm H₂O in pressure demand PAPRs, even breathing flow was over 100 L/min. For lower breathing flow, the static pressure inside respirator could be as high as 30 mm H₂O due to high supply flow. For constant flow PAPRs, the static pressure was less than the pressure demand PAPRs, however, negative pressure occurred under extremely high breathing flow. From the comfort level and positive pressure point of view, we could make suggestion to use the types of PAPRs in different workload: If we are in heavy working conditions, we must use the pressure demand PAPRs to maintain pressure positive inside the facepiece; If we are in gentle breathing conditions, we might choose constant flow PAPRs to reduce the respiratory burden.
To sum up, the pressure demand PAPRs is apparently designed for heavy working conditions. With the excessive supply air flow, the too high static pressure inside respirator is not only uncomfortable to the wearer, but the power consumption would be wasteful. Therefore, the auto-feedback system can be further improved to provide better comfort and protection.

Protective Clothing and Equipment/Respiratory Protection

Indoor Environmental Quality/Indoor Air Quality