Hexavalent chromium exposures during full-aircraft corrosion control

Area of Science:

• Occupational Health
• Materials Science
• Environmental Science

Background:

• Modern aircraft utilize aluminum alloys susceptible to corrosion.
• Organic coatings, including chromate conversion coats and epoxy primers, are primary corrosion control methods in the U.S. Air Force.
• Hexavalent chromium (CrVI) compounds are key components in these protective coatings.

Purpose of the Study:

• To quantify worker inhalation exposures to hexavalent chromium (CrVI) during aircraft corrosion control procedures.
• To assess CrVI exposure levels against established occupational exposure limits.
• To identify specific tasks contributing to elevated CrVI exposure.

Main Methods:

• Air sampling was conducted to measure time-weighted average (TWA) exposures to chromic acid and strontium chromate.
• Exposures were measured during conversion coat application, primer application, and mechanical abrasion of aircraft surfaces.
• Measured TWA exposures were compared to current ACGIH Threshold Limit Values (TLVs).

Main Results:

• Mean TWA exposure to chromic acid during conversion coat treatment was 0.48 microg/m(3), below the ACGIH TLV-TWA of 50 microg/m(3).
• Mean TWA exposures to strontium chromate were 5.33 microg/m(3) during mechanical abrasion and 83.8 microg/m(3) during primer application.
• Strontium chromate exposures significantly exceeded the ACGIH TLV-TWA of 0.5 microg/m(3).

Conclusions:

• Worker exposure to strontium chromate during aircraft maintenance exceeds safe occupational limits.
• Current corrosion control practices involving chromated materials pose significant inhalation risks.
• Additional control measures are essential to mitigate CrVI exposures if chromated coatings are retained.