Hexavalent Chromium Exposures During Full-Aircraft Corrosion Control

Abstract

Aluminum alloys used in the construction of modern aircraft are subject to corrosion. The principal means of controlling this corrosion in the U.S. Air Force are organic coatings. The organic coating system consists of a chromate conversion coat, epoxy resin primer, and polyurethane enamel topcoat. Hexavalent chromium (CrVI) is present in the conversion coat in the form of chromic acid and in the primer in the form of strontium chromate. CrVI inhalation exposures can occur when workers spray conversion coat onto bare metal and apply primer to the treated metal surface. In addition, mechanical abrasion of aircraft surfaces can generate particulates that contain chromates from previously applied primers and conversion coats. This study measured CrVI exposures during these corrosion control procedures. Mean time-weighted average (TWA) exposure to chromic acid during conversion coat treatment was 0.48 µg/m3, below the current American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV®) TWA of 50 µg/m3 for water-soluble CrVI compounds. Mean TWA exposures to strontium chromate were 5.33 µg/m3 during mechanical abrasion and 83.8 µg/m3 during primer application. These levels are in excess of the current ACGIH TLV-TWA of 0.5 µg/m3 for strontium chromate. In the absence of a change from chromated to nonchromated conversion coats and primers, additional control measures are needed to reduce these exposures.