AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Improvement of Quantitative Fit Testing Methods Using Ambient Aerosols
SHYANG-HAW YANG, Kai–Jie Yang, Chih-Wei Lin, Sheng-Hsiu Huang, Yu-Mei Kuo, Chih-Chieh Chen, National Taiwan University
Abstract Number: 66 Working Group: Instrumentation and Methods
Abstract Fit testing should be performed before the use of tight-fitting respirators. However, it may not always be conducted for various reasons, including time and cost. This study aimed to evaluate the feasibility to shorten the fit testing time by improving the instrumental settings, sampling system design, and data analysis procedure.
Experiments of fit factor measurements were divided into two mode: constant flow and cyclic flow. To simulate leakage, capillaries (10 mm in length, diameter 1.0-1.5 mm) were used to insert on N95 or N100. The ratio of total to leak flow was considered the “true fit factor, FFt”. Flow rates ranging from 5-50 L/min were adopted to study the flow dependency of fit factor. The measured fit factors were determined by concurrent particle concentration measured by a Portacount and a OPS 3330. A 1.7-m sampling tube was used to connect filtering facepiece and the aerosol instruments. 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, to explore the minimal sampling time that approximated the 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 filter penetration. Therefore, N95-companion was necessary while testing N95 respirator. For the cyclic flow 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 FFt when using the highest concentration during a breath cycle (FFmin), and it could be decided in only one breath. Consequently, with improved design, a fit test would take approximately only 12 seconds, while the whole fit testing process could be shortened from 7.5 to about 3 minutes.