the APCP manufacturer to characterize the burn rate as a function of pressure. Empirically, APCP adheres fairly well to the following power-function model: It is worth noting that typically for APCP, n is 0.3–0.5 indicating that APCP is sub-critically pressure sensitive. That is, if surface area were maintained constant during a burn the combustion reaction would not run away to (theoretically) infinite as the pressure would reach an internal equilibrium. This isn't to say that APCP cannot cause an explosion, just that it will not detonate. Thus, any explosion would be caused by the pressure surpassing the burst pressure of the container (rocket motor). Model/high-power rocketry applications Commercial APCP rocket engines usually come in the form of reloadable motor systems (RMS) and fully assembled single-use rocket motors. For RMS, the APCP "grains" (cylinders of propellant) are loaded into the reusable motor casing along with a sequence of insulator disks and o-rings and a (graphite or glass-filled phenolic resin) nozzle. The motor casing and closures are typically bought separately from the motor manufacturer and are often precision-machined from aluminum. The assembled RMS contains both reusable (typically metal) and disposable components. The major APCP suppliers for hobby use are: Aerotech Consumer Aerospace Cesaroni Technology Loki Research Gorilla Rocket Motors To achieve different visual effects and flight characteristics, hobby APCP suppliers offer a variety of different characteristic propellant types. These can range from fast-burning with little smoke and blue flame to classic white smoke and white flame. In addition, colored formulations are available to display reds, greens, blues, and even black smoke. In the medium- and high-power rocket applications, APCP has largely replaced black powder as a rocket propellant. Compacted black powder slugs become prone to fracture in larger applications, which can result in catastrophic failure in rocket vehicles. APCP's elastic material properties make it less vulnerable to fracture from accidental shock or high-acceleration flights. Due to these attributes, widespread adoption of APCP and related propellant types in the hobby has significantly enhanced the safety of rocketry. Environmental and other concerns The exhaust from APCP solid rocket motors contains mostly water, carbon dioxide, hydrogen chloride, and a metal oxide (typically aluminium oxide). The hydrogen chloride can easily dissolve in water and create corrosive hydrochloric acid. The environmental fate of hydrogen chloride is not well documented. The hydrochloric acid component of APCP exhaust leads to the condensation of atmospheric moisture in the plume and