Drum skin temperatures alone are not the best indicators for determining whether or not a coke drum has been adequately quenched and cannot be used to determine if there are any hot spots. Drum skin temperatures can be used but there are better indicators for an adequately quenched drum. Some are: < 135°F Top outlet temperature, < 5 psig at the end of the quench and < 1 psig to remove the top head, total amount of quench water used should be consistent, the amount of sour water produced is a very good indicator, and the knowledge of any change in the coker feedstock. Some crude blends produce shot coke, which makes it very difficult to quench. Drum skin temperatures can be also used for other things. We use the bottom skin temperature (< 250°F) as an interlock for removing the bottom head.