Evaluation of clothing systems to determine heat strain.

This article describes the basic evaluation process and test methodology employed when temperature extremes for clothing systems must be considered as part of the U.S. Army's Health Hazard Assessment for material in the development and acquisition process. The goals of the evaluation are to select clothing systems that minimize the hazards of heat strain and to predict the heat strain for persons wearing such clothing. Clothing evaluations begin with biophysical assessments that determine the thermal characteristics (vapor permeability and insulation) for textiles via guarded hot plate tests and for clothing systems via thermal manikin tests. The results from biophysical tests can be used to select the textile and/or clothing with the best thermal characteristics. The data from manikin evaluations also can be used in prediction modeling. Human physiological testing is best done in a controlled laboratory environment, although for realism and user acceptability field trials may also be conducted. Proven test and measurement methods must be employed, and tests must control for confounding variables; subjects serve as their own controls, and test environment and procedures are consistent between trials. The process and test methodology described can be applied to the evaluation of civilian clothing systems as well as to the military systems for which they were developed.