Drill bits and thermal lances are both perforation tools used in a variety of situations. For drill bit solutions, there exists a lot of theory regarding the proper drill bit selection for each application. However, for thermal lances, despite being a century-old tool, there is no technical information nor a theoretical framework that allows to understand its underlying science, required to properly select a thermal lance for a specific application. This article presents a theoretical framework, developing the concepts and variables that rule the thermal lances behaviour and performance. The proposed framework fits well with experimental results, therefore could be used as a guide to select the proper thermal lance for each tapping process, potentially allowing time savings leading to an increase in the profitability of furnaces operation.