An automated system for quantitative respirator fit testing by negative pressure was evaluated by comparison testing with a computerized aerosol fit test system (Dynatech Frontier Model 260A). The new negative pressure system measures leakage flow while inspiratory pressures are sustained in a respirator facepiece rather than by pressure decay. Four phases of comparison testing were graduated by level of control, ranging from non-subject tests with hypodermic needle leakages to fit tests of 125 Air Force personnel. Throughout the series of tests, negative pressure fit factors were consistently more conservative than aerosol fit factors and showed less variability. Leakage flow rates measured by the negative pressure instrument were highly correlated with leak needle cross-sectional area as predicted by principles of air-flow physics. Comparison of subject and non-subject generated aerosol fit factors indicated significant aerosol losses, possibly due to streamlining and respiratory tract deposition. Negative pressure fit factors were not affected by these subject-related losses.

A negative pressure quantitative fit testing device was used to test the effect exercise protocol has on leakage rates into a negative pressure respirator. Modified exercise protocols were developed for use with the negative pressure system. Aerosol data was analyzed to determine the effect exercises have had on leakage rates using other QNFT systems. Results show that the position of the head affects the amount of leakage into the facepiece. Mean leakage into the respirator mask increased for all positions tested in one phase of the study. However, statistical analysis of the data showed that the increase was not statistically significant. Aerosol data analysis also showed that increases in leakage into the mask were not statistically significant. Conclusions drawn from this study are that although movement of the head may affect the leakage into a respirator it is not significant enough to alter the protection afforded the worker.

This study determined the parameters which affect the internal mask inspiratory pressure and flow rate during respirator wear. The average inspiratory pressure and inspiratory flow rate were measured on 30 subjects who performed various submaximal work rates on a cycle ergometer while wearing air purifying respirators. The half-mask and full-face respirators were equipped with three levels of cartridge resistance. The results indicated that work rate, cartridge resistance, and mask type affected the inspiratory pressure and flow rate significantly. The findings of this study would allow the quantitative negative pressure respirator fit test to evaluate respirator fit over a wide range and representative of actual work condition.