Correcting Coal Miner Respirator Total Inward Leakage Values for Respiratory Tract Deposition

Area of Science:

• Occupational Health and Safety
• Industrial Hygiene
• Respiratory Protection

Background:

• Workplace respirator efficacy studies commonly measure total inward leakage (TIL) for particulate contaminants.
• Early studies, like the 1970s Harris study in coal mines, used inside-the-facepiece sampling.
• Exhaled air depletion of dust due to respiratory deposition led to underestimated TIL values and overestimated respirator efficacy.

Purpose of the Study:

• To develop a method for correcting historical TIL values from the Harris study.
• To account for respiratory tract deposition and particle size-selective cyclone sampling.
• To re-evaluate respirator efficacy based on corrected exposure data.

Main Methods:

• Applied a correction method to the Harris study's reported TIL values.
• Incorporated respiratory tract deposition and cyclone sampling characteristics.
• Utilized estimated coal mine particle size distribution data.
• Assessed compliance with the assigned protection factor (APF) of five.

Main Results:

• Corrected TIL values were found to be 1.69 times higher than initially reported.
• The multiplicative factor accounts for particle deposition and sampling bias.
• A significant proportion (4/5) of quartermask respirators in the Harris study did not meet the APF of five criterion with corrected TIL values.

Conclusions:

• The original Harris study underestimated respirator inward leakage due to respiratory deposition.
• Corrected efficacy data indicates that many quartermask respirators failed to provide adequate protection.
• Re-evaluation of historical respirator studies is crucial for accurate occupational exposure assessment.