AIMS: To develop test methods and evaluate survival of Bacillus anthracis ∆Sterne or Bacillus thuringiensis Al Hakam on materials contaminated with dirty spore preparations after exposure to hot, humid air using response surface modelling. METHODS AND RESULTS: Spores (>7 log₁₀) were mixed with humic acid + spent sporulation medium (organic debris) or kaolin (dirt debris). Spore samples were then dried on five different test materials (wiring insulation, aircraft performance coating, anti‐skid, polypropylene, and nylon). Inoculated materials were tested with 19 test combinations of temperature (55, 65, 75°C), relative humidity (70, 80, 90%) and time (1, 2, 3 days). The slowest spore inactivation kinetics was on nylon webbing and/or after addition of organic debris. CONCLUSIONS: Hot, humid air effectively decontaminates materials contaminated with dirty Bacillus spore preparations; debris and material interactions create complex decontamination kinetic patterns; and B. thuringiensis Al Hakam is a realistic surrogate for B. anthracis. SIGNIFICANCE AND IMPACT OF THE STUDY: Response surface models of hot, humid air decontamination were developed which may be used to select decontamination parameters for contamination scenarios including aircraft.