In-process, refers to stages of manufacture of an original product or an application of that product into another product. The material is considered in-process, if it is in an operation, process, or manufacturing stage where it is being used, changed, transported, mixed or otherwise modified or incorporated into the process or product.

Two main divisions exist when discussing explosives: substance and articles. Substances refer to the actual explosive (powders, grains, pellets, etc.). Articles refer to items, which contain explosive substances (detonators, igniters, inflators, etc.). Both substances and articles can mass react depending on the explosive materials they contain and the design configuration used. Different tests are needed to evaluate the propagation potential of substances and articles.

For classification purposes, one looks at both the sensitivity and reactivity of the substance or article. Sensitivity refers to how easily a material or article is initiated due to various stimuli. Reactivity refers to what type or size of event is produced once initiation occurs. When the sensitivity and reactivity of a substance or article is properly characterized, the data can also be used to improve the safety and application of the material in addition to in-process classifications as presented here.