Graduation Year

2014

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Environmental and Occupational Health

Major Professor

Yehia Y. Hammad, Sc.D.

Committee Member

Thomas Mason, Ph.D., M.S.

Committee Member

Steven Mlynarek, Ph.D., C.I.H.

Committee Member

Edwin Rivera, Ph.D.

Committee Member

Rene Salazar, Ph.D., C.I.H.

Keywords

Aerosol, Filter, Head Straps, Leakage, PPE

Abstract

Certain N95 FFR models that staple the head straps directly onto filtering material are commercially available. This method of assembly can tear or reduce fiber density in the immediate area surrounding the staple punctures. Five N95 FFR models were evaluated to determine if staple punctures on the filter medium reduce the protection offered by the respirators.

Total penetrations were measured with the staple punctures intact and when stretching the head straps a distance equivalent to a 95% male head circumference. Filter penetration were measured by sealing the staple punctures. Aerosols of 200, 500, and 1000 nm were used to challenge respirators at 28 and 85 Liter/min flow rates. Staple punctures were visually inspected by macrophotography with a light source on the opposing side of the punctures.

Three FFR models had greater mean leakages than the remaining two. However, only two FFR models had statistically significant greater total penetrations than filter penetrations. Pulling the head straps increased total penetration, but was not statistically significant. Filter penetrations were greatest at 85 Liter/min and 200 nm, while leakages were greatest at 28 Liter/min flow rate and 1000 nm.

Leakage through the staple punctures had greater contributions to total penetration than filter penetration allowing a greater percentage of 1000 nm particles into the breathing zone. Leakage was dependent on the tearing of the filter material or the reduction of fiber density near the puncture, regardless of filter efficiency. Total penetration to filter penetration ratios showed that leakage was greater than filter penetration 15 fold for 1,000 nm. This value is similar to what has been reported for face seal leaks on human subjects. Protection factors were reduced from ~930 to ~60 when the staple punctures created a tear. N95 FFR with stapled head straps that puncture the filter medium should be avoided because they can reduce protection to the user.

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