Facepiece−to−face leakage evaluation using a helium leak detection method

Abstract

Assurance of a proper fit and thus maximum respiratory protection to the user of respiratory protective devices is the subject of increasing emphasis by the government under the Occupational Safety and Health Act. The primary method of assessing protection is to measure the amount of leakage from a challenge atmosphere surrounding a test subject into the breathing zone inside the respiratory protective device being worn. Methods currently in use are either largely subjective, present some hazard to the test subject, or are subject to unpredictable errors. This paper presents a simple method of using physiologically inert helium as a diluant in a respirable mixture of air, and then detecting the amount of helium leaking into the respirator facepiece with a mass spectrometer helium leak detector equipped with a special sampling and calibration system. Data obtained indicate a capability of repeatability assessing leakage rates as low as one standard cubic centimeter per minute, translating roughly into determining protection factors of better than 10000 for full facepiece respirators. Shortcomings of the available equipment and suggestions for improving the accuracy and rapidity of data collection are discussed.