A closed system drug transfer device or "CSTD" is a drug transfer device that mechanically prohibits the transfer of environmental contaminants into a system and the escape of hazardous drug or vapor concentrations outside the system. Open versus closed systems are commonly applied in medical devices to maintain the sterility of a fluid pathway. CSTDs work by preventing the uncontrolled inflow and outflow of contaminants and drugs, preserving the quality of solution to be infused into a patient. Theoretically, CSTDs should enable complete protection to healthcare workers in managing hazardous drugs, but possibly due to improper handling or incomplete product design, contaminants can still be detected despite use of CSTDs.[1]