Date of Degree
PhD (Doctor of Philosophy)
Occupational and Environmental Health
First Committee Member
Thomas M Peters
Second Committee Member
T. Renee Anthony
Third Committee Member
Matthew W Nonnenmann
Fourth Committee Member
Nathan B Fethke
The research presented in this doctoral dissertation strived to increase knowledge with respect to respirators performance in the workplace by evaluating particle penetration and breathing resistance (BR) of N95 filtering face-piece respirators (FFRs) under simulated air environmental conditions, determining maximum particle penetration of uncertified dust masks (UDMs) against sodium chloride (NaCl) and BR of UDMs and FFRs when challenged against Arizona road dust (ARD), and evaluating BR of FFRs while performing power washing in swine rooms.
A novel test system was used to measure particle penetration and BR of two N95 FFRs under modified environmental conditions. NaCl particle penetration through the FFR was measured before and after the BR test using a scanning mobility particle sizer. BR of the FFR was measured by mimicking inhalation and exhalation breathing, while relative humidity and temperature were modified. BR was evaluated for 120 min under cyclic flow and four temperature and relative humidity air conditions. The BR of the FFRs was found to increase significantly with increasing relative humidity and lowering temperature upstream the FFR (p < 0.001). Measured particle penetration was not influenced by the simulated air environmental conditions. Differences in BR was observed between FFRs indicating that FFRs filtering media may perform differently under high relative humidity in air.
In the second study, the maximum particle penetration of five commercially available UDMs was evaluated against NaCl aerosol. Particle penetration was carried out as specified by National Institute for Occupational Safety and Health (NIOSH) to certify N95 FFRs (42 CFR Part 84). Particle penetration was found to vary between 3% and 75% at the most penetrating particle size. In addition, the effect of mass loading on BR of UDMs and FFRs over time was evaluated. ARD was used as the loading dust and BR was measured for 120 min on UDMs and FFRs. BR was found to increase differently between the tested UDMs and FFRs. Further analysis of the UDMs and FFRs external layer suggest that the development of the particle dust cake during mass loading may be influenced by differences of the external layer.
In the third study, field research was conducted to evaluate BR of two N95 FFRs while performing power washing in swine rooms. A member of the research team wore the FFR while power washing swine rooms. Every 30 min the team member stopped power washing, BR was measured and power washing continued. At the end of the 120 min trial, the FFR model was switched and the team member continued to power wash the rest of the room. Results demonstrated that BR of the tested FFRs did not increased during power washing in swine rooms (FFR 1, p = 0.40; FFR 2, p = 0.86). Power washing was found to have an effect in the temperature and relative humidity inside the rooms. Based on this study, FFR wearer should expect no increase in BR over 8 hr of power washing, decrease health risk by wearing the FFR and no need to replace the FFR during the power washing task.
Space is a concept we are all familiar with; yet when it comes to giving a precise definition or characterization of the notion, things become complicated. For example in mathematics there are many kinds of spaces, like inner product spaces, normed vector spaces, metric spaces, and topological spaces. Think of a set of points along with a set of neighborhoods of each point, satisfying a collection of universal truths relating said points and neighborhoods, call this a topological space.
A manifold is a topological space that locally looks like the Euclidean space near each point but globally it may not. Manifolds come in all dimensions; examples of 1-dimensional manifolds are lines and circles, and some 2-dimensional manifolds (called surfaces) are spheres, planes, and tori (think of doughnuts). A smooth manifold is a type of manifold on which we can do calculus, like the derivatives and integrals we learned in high school. Now consider a sphere and a sheet of paper touching the north pole of the sphere, the sheet of paper is the tangent space of the pole. Contact geometry is the study of a geometric structure called a contact structure on a smooth manifold M, given by a hyperplane subset of the disjoint union of tangent spaces of M satisfying certain properties and conditions.
On a 3-dimensional manifold, a contact structure is an arrangement of planes called contact planes. There is more than one way of arranging these planes to create a contact structure, and sometimes even thought the contact planes might look different, the contact structures themselves are equivalent. Contact structures basically come in one of two types, tight or overtwisted. In this work we show how a particular col- lection of contact structures falls under the overtwisted category, and give an explicit construction for a family of universally tight contact structures.
xi, 88 pages
Includes bibliographical references (pages 83-88).
Copyright 2015 Joel A. Ramirez
Ramirez, Joel Amilcar. "Evaluation of particle penetration and breathing resistance of N95 filtering face-piece respirators and uncertified dust masks." PhD (Doctor of Philosophy) thesis, University of Iowa, 2015.