I've heard of interlocks at chemical plants? What are they? How do they work? Can you give me an example?
The nature of chemical plants is such that there has to be some order to things else the end result will not be what is desired, or worse a very unsafe condition could exist. Thus there are interlocks to help avoid these situions.
Some interlocks could be as simple as a too high or low temperature. If for example a chemical reaction is only safe at a certain temperature then the system may not allow the plant operator to start that process if the temperature is too high or too low. The same for pressure, flows etc. Another example is a boiler. Every boiler should have an interlock that prevents it from being started if the water level is too low. Some gas furnaces have interlocks that prevented them from being started if there is not enough combution air, or too much or too little gas, or if the purge sequence has not been completed.