Mixmaster exposure to dust during mixing of wildland fire retardant chemicals

Abstract

A study was performed at two air tanker/retardant bases to determine the mixmaster’s exposure to dust derived from mixing dry fire retardant compounds. Personal sampling for both inhalable and respirable dust was conducted while the mixmaster mixed fire retardant compounds to form a retardant slurry. Personal samples were also analysed for a colorant in the retardants and hydrogen cyanide. Hazard quotients were calculated for average and upper-end use scenarios using a risk assessment model from Labat-Anderson, Incorporated.

The exposure analysis revealed that the 8-h time weighted average (TWA) concentrations were within applicable occupational exposure limits for the inhalable and respirable dust fractions as well as for the colorant and hydrogen cyanide. When the mean inhalable exposure concentration was used to calculate chemical intake, hazard quotients were above 1 at both retardant bases, indicating a potential for non-carcinogenic health effects.

Exposure control methods recommended from this study include substitution of a liquid concentrate fire retardant, installation of local exhaust ventilation systems, good housekeeping and personal hygiene. We also recommend the use of personal protective equipment including a filtering facepiece, half-mask respirator; eye protection, and protective clothing such as gloves and coveralls.