ASP Defenders were specifically designed as a dispersion system for chemical irritants. Rather than filling a standard aerosol can with OC (Oleoresin Capsicum), Defenders incorporate a proprietary container, specially produced valve system and patented dispensing mechanism. They are precision machined from aerospace aluminum and solid brass. The entire unit is o-ring sealed.Heat Inserts contain approximately three 1/2-second bursts of 10% Oleoresin Capsicum of a Two Million Scoville Heat Unit (SHU) strength. Heat Inserts are date coded to assure reliability. After this date, your Insert should be disposed of in accordance with the environmental regulations in your area.Test Inserts contain an inert carrier and are used for training purposes only. Compatible with ASP Palm Defenders.