- 學位論文
1. 呼氣閥動態洩漏測試系統的研發 2. 呼吸防護具新式高保護係數呼氣閥之研發
Part I. Development of a dynamic leakage test system for exhalation valves Part II. Development of a Novel High Protection Exhalation Valve for Respirator
摘要
Part I 呼吸防護具是在無法使用工程控制的情況下，用來保護工作人員避免接觸空氣污染物的一種個人防護具。呼吸防護具的洩漏途徑有三種：濾材洩漏、面體密合洩漏和呼氣閥洩漏。正常使用下，呼氣閥的洩漏對於總洩漏的貢獻比例較小，然而在高防護係數的濾材和高密合度需求時，由於經過濾材與臉面縫隙的空氣阻抗變高，呼氣閥的洩漏就變得相對重要。現有呼氣閥的測試規範有澳洲紐西蘭所使用的AS/NZS 1716-1994 (Australian) 和美國的42CFR part 84 (USA)，規範一個新的呼氣閥在負壓25毫米水柱的負壓抽引下，每分鐘的空氣洩漏率不能超過三十毫升。有研究指出現有對於呼氣閥的測試規範方法並不能代表真實使用下呼氣閥的洩露，因此本研究建立了呼氣閥的動態測試系統來和靜態的規範測試結果作對比。結果指出，動態洩漏和靜態洩漏有不錯的相關性，但在某些評估呼氣閥的情況下，靜態測試並不能完全取代動態測試，譬如閥蓋設計影響動態洩漏的效應以及呼氣閥微粒負載效應之探討，此兩種效應的探討在靜態測試方法中是無法做到的。因此即使靜態測試和動態測試有不錯的相關性，在評估呼氣閥實際使用下的效能以及研發新型呼氣閥時，動態洩漏測試還是有其必要性。 Part II 呼吸防護具為保護勞工避免接觸空氣污染物的最後一道防線，然而長時間佩帶呼吸防護具會造成面體內累積高溼度和熱而造成使用者感到不適。因此呼氣閥的設計可用來減少使用者的不適感。呼吸防護具的洩漏途徑有三種：濾材洩漏、面體密合洩漏和呼氣閥洩漏，正常情況下呼氣閥的洩漏量對總洩漏量的貢獻很小，然而需要使用高防護係數的呼吸防護具時，由於經過濾材與臉面縫隙的空氣阻抗變高，呼氣閥的洩漏就變得相對重要。現今澳洲紐西蘭所使用的規範AS/NZS 1716-1994 (Australian) 和美國的規範42CFR part 84 (USA)要求一個新的呼氣閥在負壓25毫米水柱的負壓抽引下，每分鐘的空氣洩漏率不能超過三十毫升，此規範測試方法基本上為靜態測試方法。然而為了評估呼氣閥真實使用時的洩漏且提升呼氣閥的效能，在本研究中建立了呼氣閥的動態洩漏測試系統來研發洩漏更少的新型呼氣閥，實驗結果顯示新式的呼氣閥設計可減少動態洩漏，僅使用一段空管做為閥蓋就有動態洩漏減少的效應產生，且若在閥蓋內填充介質，如海綿或蜂巢板，可更加地減少動態洩漏。更進一步地藉由改變海綿的厚度和孔隙度則可大幅地提升呼氣閥的效能。此設計在本研究中應用在一個超過法規標準洩漏6倍的呼氣閥，其洩漏率可降至0.0005%，約減少其原本洩漏的99.95%，此結果點出了此新式呼氣閥的設計可確保即使呼氣閥在使用時損壞也不會讓使用者因為呼氣閥的過量洩漏而產生過量的暴露，因此在預防的觀點上，此新式呼氣閥設計能有效地保障使用者的安全。
並列摘要
Part I Respirators are commonly used to protect workers from inhaling air contaminants, especially when engineering and work practice controls fail to reduce workers’ exposure to acceptable levels. In general, there are three potential routes of leakage into respirators: filter penetration, facial seal leak and exhalation valve leak. Normally, exhalation valve leaks less compared to the other two leak routes. However, when a higher protection (more filter material and better respirator fit) is needed, the valve leakage becomes more important because of the leakage re-distribution. Current static certification test employed by USA and Australia requires leakage into new exhalation valves should not exceed 30 mL/min at a constant suction head of 25 mmH2O. This static test may not able to reflect the overall leak characteristics of exhalation valve when used under practical cyclic flow mode. Therefore, a dynamic leakage test system needs to be developed. A dynamic leakage test apparatus developed in this work consisted of an aerosol generation system, a breathing machine, and a cylinder simulating respirator cavity. The cylinder cavity was connected to aerosol chamber with an exhalation valve as the interface. With the breathing simulator functioning, the air resistance caused by the filter medium can be created by controlling the clean air flow supplied to the cylinder cavity. A condensation particle counter was used to monitor the aerosol concentration inside the cylinder cavity. The results showed the static leakage correlated well with the dynamic test data. However, the dynamic method is apparently more versatile and should not be substituted or replaced by the static test method. For example, static method cannot be used to study the effect of aerosol loading on the valve membrane and/or valve seat, which is likely to occur under cyclic flow. Also, the modification of the valve cover showed significant decrease in valve leakage, but the static test method was insensitive to the benefit. Part II Respirator is the last resort to protect workers against air contaminants. However, the accumulated heat and humidity often make wearers feel uncomfortable, especially for workers wearing respirators for a long period of time. Respirators equipped with an exhalation valve reduce the level of discomfort. In general, there are three routes of leakage on respirators, namely filter penetration, facial seal leak and exhalation valve leak. Usually, the exhalation valve leakage is the least among all potential leak pathways. Nevertheless, when a higher protection is needed, the exhalation valve leakage will become more important due to the increase of air resistance resulted from the thicker filter medium and better fit of the respirator to the wearer’s face. The static leakage test method currently employed by USA and Australia cannot reflect the leak characteristics when the respirators are used under practical cyclic flow mode. In order to characterize the leak behavior of exhalation valve under cyclic flow and design new exhalation valve, a dynamic leakage test system was built. By adding a piece of foam filter, honeycomb, or simply a tube, on top of the valve membrane, the new device was found to reduce the mass change between the clean exhaled breath and the contaminated ambient air. That means lower exhalation valve leakage, and therefore higher protection. To make the respirators user friendly, i.e., handy, portable, miniaturized, the use of highly porous materials, such as foam filters (100 ppi and above) is recommended. The used of porous materials or strengthening devices not only reduce the mass exchange but also help filter the contaminants if they are aerosol particles. The addition of this foam certainly increased the air resistance during exhalation, but the benefit is tremendous decrease in exhalation valve leakage. For example, under breathing flow of 10.5 L/min (tidal volume of 0.7 L, and breathing frequency of 15 breath/min), the maximum exhalation resistance increase from 4.8 to 6 mm H2O, a 25% increase, but the exhalation valve leakage decreased from 0.45 to 0.0005%, a 99.99% decreases by the use of the foam disc with 80 ppi and 24 mm thickness.