At one time, vapors that are potentially harmful to the environment or to human health were simply allowed to escape into the atmosphere. Each time an automobile consumer filled the gas tank, for example, gasoline vapors escaped into the air. As the hazards of these emissions became more evident, the use of closed systems of pipes, valves, compressors, and other components became more prevalent. In most systems, those vapors are compressed to a liquid and returned to their original source. Vapor recovery systems not only protect the environment, but conserve resources that might otherwise be wasted.