Biomedical subjects
C E Colton
Publications and source records attributed to C E Colton.
The impact of wear time.
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Quantitative fit testing techniques and regulations for tight-fitting respirators: current methods measuring aerosol or air leakage, and new developments.
Until a few years ago, only two quantitative fit testing (QNFT) techniques were available and accepted by U.S. Occupational Safety and Health Administration (OSHA) regulations. In the 1980s and 1990s, several new and fundamentally different QNFT methods were developed. Two of the newer methods are commercially available and are accepted by OSHA as suitable alternatives. In this article the principles of operation of the OSHA-accepted and of some newly developed but not yet approved QNFT techniques are explained, and each technique's major advantages and disadvantages are pointed out. Emphasis is given to negative-pressure air-purifying respirators, as they are in most frequent use today. The requirements and recommendations for fit testing positive-pressure respirators are discussed as well. Finally, the presently available QNFT standards and regulations are summarized to assist the user in making fit testing decisions.
Respiratory program develops training, fit-testing routines. Respiratory equipment minimizes exposure to potentially hazardous airborne contaminants.
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Review of respirator performance testing in the workplace: issues and concerns.
Performance capability of respirators has traditionally been evaluated by testing components of the respirator (e.g., filter efficiency), facepiece fit, total inward leakage, or some other measure of performance evaluated under laboratory conditions. In recent years, increased emphasis has been placed on development of test methods suitable for evaluating respirator performance in the workplace. The goal of such testing is to evaluate the level of protection provided by respirators in the work environment. The AIHA Respiratory Protection Committee believes that workplace testing of respirators has the potential to be an excellent tool for increasing knowledge about the effectiveness of respiratory protection. However, a number of technical issues remain to be addressed before optimal test protocols and data analysis methods can be defined. The progress made to date in workplace testing will be reviewed, and broader discussion about key elements that must be considered when developing guidelines for testing respirators in the workplace will be initiated.
AIHA evaluates how respirator protection is measured in workplace.
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How protective are respirator assigned protection factors: an uncertainty analysis.
This investigation evaluated the risk of overexposure for a selected assigned protection factor by performing Monte Carlo simulations. A model was constructed to assess respirator performance by calculating the concentration inside the respirator. Estimates of the factors that affect respirator performance were described as distributions. The distributions used a worst case estimate for concentration in the workplace, the worst case for respirator performance (the fifth percentile person), and the worst case for exhalation valve leakage. A Monte Carlo analysis then provided estimates of the percentage of time that concentration inside the respirator exceeded the occupational exposure limit (OEL). For a half-facepiece respirator with an APF of 10, the calculations indicated a low risk of being exposed above an OEL, with mean exposures being controlled well below an OEL.
The effect of inhalation resistance on facepiece leakage.
Air purifying respirators use filters to remove particulate air contaminants. Resistance to airflow generally increases as the filter loads and a "filter cake" is formed. It has been recommended by ANSI and the Occupational Safety and Health Administration that filters should be replaced when the wearer notices they are hard to breathe through. Repeated faceseal leak rate measurements were made during respiratory wear over a range of simulated breathing resistances from 5.6 to 19.6 mm (0.22 to 0.77 inches) of water. The measured faceseal leak rates increased as the breathing resistance increased and varied depending on the initial leak rate at the 5.6 mm pressure. The increase in faceseal leak rate from 5.6 to 19.6 mm breathing resistance was as high as a factor of 4. Theoretically, a person with an initial respirator penetration of 2.5% could have that value increase to 10% as filter loading increased breathing resistance by 14 mm. Some research has shown that breathing resistances between 60 and 140 mm of water would be "noticeable but well tolerated." It is not known if workers would be able to detect an increase in breathing resistance that would lead to a significant increase in faceseal leakage. These data suggest a need to establish a replacement schedule for all filters used in the workplace. How often a filter should be replaced is difficult to determine. Breathing resistance would vary depending on the individual filter and aerosol loading characteristics, the concentration of the aerosol in the workplace, and breathing rates.