The NIOSH Total Inward Leakage Project

While TIL testing under lab conditions is not expected to reflect expected field performance, it represents a performance criterion that will influence PPE design.

• By Roland Berry Ann
• Oct 31, 2007

The National Institute for Occupational Safety and Health (NIOSH) conducts a range of efforts in the areas of research, information, and service. The NIOSH program portfolio focuses on relevance, quality, and impact. This is achieved through strong involvement of partners and stakeholders through the entire research continuum (conceiving, planning, conducting, translating, disseminating, and evaluating). The programmatic and support structures provide a foundation for staff to carry out its mission to provide national and world leadership to prevent work-related illnesses and injuries.

The NIOSH program portfolio is organized into eight industry sectors (e.g., mining), 15 cross-sector programs (e.g., personal protective technology), and eight coordinated emphasis areas (e.g., nanotechnology). These programs are centered around adverse health outcomes, statutory programs, and global efforts. The Personal Protective Technology (PPT) Program activities include the technical methods, processes, techniques, tools, and materials that support the development and use of personal protective equipment worn by individuals to reduce effects of their exposure to a hazard.

NIOSH created the National Personal Protective Technology Laboratory (NPPTL) in 2001, when Congress underscored the need for improved personal protective equipment and encouraged research for personal protective technologies.  NPPTL manages the NIOSH PPT Program. The mission of both the PPT program and NPPTL is to prevent work-related injury, illness, and death by advancing the state of knowledge and application of personal protective technologies. The vision is to be the leading provider of quality, relevant, and timely PPT research, training, and evaluation.

Starting the TIL Project
A PPT program project involves establishing total inward leakage (TIL) laboratory test capability and performance requirements for respirator certification.

The inward leakage of a respirator is determined by measuring the concentration of a challenge aerosol outside of the respirator, as well as the concentration within the breathing zone. Respirator fit testing normally considers face seal leakage. Total inward leakage defines a protective level achieved by a respirator when the contributions of all leakage paths are considered.

The TIL is defined as the ratio of the external concentration to the breathing-zone concentration. While the total inward leakage testing performed under laboratory conditions is not expected to reflect expected actual field level PPE performance, it does represent a criterion for performance that will influence PPE design and performance. The project is initially addressing the performance requirement for half-mask respirators, including elastomeric and filtering facepiece styles. Other classes of respirators will be incorporated into the program following completion of the half-mask project.

TIL testing is intended to quantify the ability of respirators to fit individuals having a defined range of facial dimensions and cannot replace individual fit testing to ensure the respirator fits the individual user.

The TIL performance requirements will be based on the performance of the current respirators in the class. The performance requirements will be based on the state-of-the-art respirator performance, accounting for differences between laboratory test conditions and workplace conditions. The TIL test will use a panel of subjects with a range of facial dimensions, and the respirators will be tested for performance to those sizes specified by the respirator manufacturer.

The exercises used to stress the facepiece-to-face seal will be similar to those identified in the OSHA respiratory protection standard.

This photo sequence shows some of the standard tests designed to stress the seal of the respirator. This one, depicting normal deep breathing, has the subject breathe slowly and deeply without talking while in a normal standing position, taking care not to hyperventilate. Standing in place, the subject slowly turns his/her head from side to side between the extreme positions on each side. The head is held at each extreme momentarily so the subject can inhale at each side. Standing in place, the subject slowly moves his/her head up and down and is instructed to inhale in the up position. The probe in the respirator is used to obtain "in mask" samples for the respirator fit testing equipment to calculate a fit factor. The clear tubing from the respirator fit testing equipment connects into the probe to facilitate sampling and measure the number of particles inside the mask, while the blue tube measures the number of air particles air.

This article originally appeared in the November 2007 issue of Occupational Health & Safety.