Many hazardous, corrosive, toxic, and environmentally-unfriendly chemicals are used in the processing industry. These chemicals require careful monitoring during use, transportation, and handling. In a basic text it is not possible to cover the above-mentioned sensors’ availability and precautions in their applications, but just to make the student aware of their existence. Analysis labs and control rooms must meet code; further information can be obtained from the ISA series RP 60 practices. All processing plants and labs will have an alarm system which can shut down certain operations if a problem occurs. These systems are regularly tested and are often duplicated to provide built-in fail-safe features such as redundancy as protection against sensor failure.