A positive pressure system for selective human exposure to gas and particulate mixed atmospheres.

Introduction: Exposure to air pollution containing particulates (PM) and gas-phase volatile organic compounds (VOCs), is a leading cause of human morbidity and mortality globally. Devising effective protective public health strategies requires an assessment of the relative contribution of PM and VOCs to the health effects of air pollution exposure.

Methods: To enable studies of VOCs isolated from mixed atmospheres, we developed a positive air pressure exposure system that permits the subject to breathe unimpeded by the pressure drop imposed by filtering respirators. This system uses pumps to draw air through respirator filters and delivers it to a modified positive pressure respirator at a flow rate that exceeds the ventilatory requirements of the wearer, while preventing infiltration of the surrounding atmosphere.

Results: Tests showed negligible leaks (<5% flow reduction) and minimal VOC losses (95% recovery) to the system. When tested using an atmosphere containing woodsmoke, PM filters showed effective exclusion of particulates but minimal losses of VOCs, while activated carbon based cartridges effectively removed gaseous compounds and PM. A team member exercising moderately in a woodsmoke atmosphere for 2-hours reported no perveivable odors and experienced no discomfort during an exposure using charcoal filter cartridges.

Discussion: We report the development and validation of a novel human exposure system that allows selective exposure to the gaseous fraction of a mixed atmosphere. This system allows for moderate to vigorous exercise of the study subject and can be used in place of an exposure chamber, making it compatible with clinical and field studies.