For years, fire departments have been utilizing chemicals to improve the effectiveness of water, thereby creating greater knockdown efficiency and increased firefighter safety. The additives in this water are sold in high concentration and require mixing to form a solution at percentages dictated by the application, or as recommended by the manufacturer. Hundreds of these concentrates are available today, but the majority fall into four basic categories: Class A Foam, Class B Foam, Emulsifiers and Gels.