環境微粒法定量密合度測試方法改進

Abstract

當作業人員第一次使用緊密接合式呼吸防護具前，必須通過密合度測試，且定期（例如：每年）與不定期（例如：佩戴者的體重變化達百分之十以上時）都需要重新測試。進行一次密合度測試大約需要7到8分鐘的時間，雖然密合度測試可以確保呼吸防護具是否能提供足夠的保護，但是實際上，可能因為其操作耗時而無法完全照規定執行，因此，若能減少密合度測試所花的時間，將能讓雇主、使用者、與呼吸防護計畫管理人員更有意願執行密合度測試，確保作業者之健康。此研究之目的為深入探討現行環境微粒定量密合度測試方法各軟硬元件的特性，研析是否能從儀器性能、採樣系統、與資料分析進行修正與改進，以降低執行密合度測試所需之時間。

本研究中關於密合度的探討，可分兩階段進行：固定流量（濾材流量與洩漏流量之和）及呼吸模擬器（潮氣量與呼吸頻率之組合）測試。洩漏的模擬是以管長為10 mm，不同管徑之毛細管(1.0、1.5 mm)為之，並監測2-50 L/min固定流量通過N95與P100兩種口罩之壓降下，各毛細管的洩漏流量。總流量與毛細管流量之比率即為『正確密合度，FFt』。實際以環境微粒進行密合度量測時，將毛細管插在口罩上模擬洩漏，微粒量測儀器使用TSI Portacount與OPS 3330，採樣管長度為1.7公尺，後端以2-50 L/min的固定流率抽氣以比較兩台儀器量測值（相對於正確密合度）之準確度。本研究也分析不同的呼吸型態（潮氣容積：0.5-1 L、5-20次�每分鐘）、肺部沉積（後端是否接HEPA）對於密合度測試時口罩內微粒濃度的影響，並據以計算出能準確決定密合度的最短採樣時間。 實驗數據顯示，Portacount的微粒測量反應時間約為5秒，而OPS 3330約為2秒，定流率測試的結果顯示，使用P100口罩時，密合係數皆能與FFt相近；但若使用N95口罩，由於會有部分微粒穿透濾材進入口罩中，密合係數將會低估，因此，在量測N95口罩之密合係數時，Portacoumt在大於10L/min的操作流量時，須將N95-companion開啟才能與FFt相近，OPS則是超過30L/min才會受到濾材穿透的影響。由於呼吸時，口罩內微粒濃度會有上下起伏的現象，現行方法為計算採樣40秒之平均值，相較FFt有明顯高估的情形，本研究使用呼吸中之最高微粒濃度計算最低之密合係數（FFmin），較能與FFt相近，且OPS因為其反應時間較快，可以測量出較接近FFt的數值。若降低呼吸頻率時，能讓儀器有較足夠的時間反應，兩台儀器測量之FFmin能與FFt相近且穩定，可將採樣時間縮短為12秒，因此，整套密合度測試可從7.5分鐘縮短至約3-4分鐘。

Fit testing should be performed before the first use of tight-fitting respirators, and re-testing should be done annually. However, it may not always be conducted for various reasons, including time（>7 mins）and cost. As a result, reduced fit testing time would help increase the willingness of the employers, users, and respiratory protection programmer to implement fit testing, which in turn improves health protection This study aimed to evaluate if the fit testing time could be shorten by improving the instrumental settings, sampling system design, and data analysis procedure. In this study, investigation of the fit factors was divided into two levels: experimental testing with constant flow rates, simulation tests using a breathing machine（combination of tidal volume and breathing frequency). To simulate leakage, capillaries that were 10 mm in length with different diameters（1.0 mm-1.5mm）were used were inserted onto the respirators. The ratio of total and leak flow rate was considered the “true fit factor” in this study. Ambient particles were passed through the capillaries at constant flow rates of 5-50 L/min under the pressure drop of N95 and P100 respirators. The measured fit factors were determined by concurrent particle concentration measured by TSI Portacount and OPS 3330 with 1.7 m sampling tube in length. In addition, the effects of breathing pattern（tidal volume: 0.5-1 L, frequency: 5-20 times/min）and lung deposition（with/without HEPA filter behind the respirator）on in-mask particle concentration during fit testing were analyzed. The results were used to explore the minimal sampling time that approximated the “true fit factor, FFt”. Results showed that the particle measurement response time for Portacount and OPS were approximately 5 and 2 seconds, respectively. For P100 respirators, most measured fit factors were similar to the FFt, whereas there was an underestimation while using N95 respirator due to particle penetration. Therefore, N95-companion was necessary while using N95 respirator. For the breathing tests, the fit factor was overestimated because the sampling tube was connected onto the facepiece where filtered air was partly sampled. The higher the breathing flow rate, the more the fit factor was overestimated. On the other hand, the measured fit factor would be close to the “true fit factor” when using the highest concentration during a breath（FFmin), and it could be decided in only one breathing. Consequently, with improved design, a fit test would cost approximately only 12 seconds, where the whole fit testing process could be reduced from 7.5 to about 3 minutes.