Although the primary explosive itself is generally a more sensitive and expensive compound, it is only used in small quantities and in relatively safely packaged forms.
Triggering sequences are used in the mining industry for the detonation of ANFO and other cheap, bulk, and insensitive explosives that cannot be fired by only a blasting cap or similar item.
An example of a low-explosive train is a rifle cartridge, which consists of High-explosives trains can be either two-step (e.g., detonator, [containing primary explosive] and dynamite / other sensitive secondary) or three-step configuration (e.g., initiator, [detonator, compound cap or NPED] booster of intermediate explosive, and main charge of insensitive secondary explosive).
Thus, an explosive booster is used to deliver a sufficient shockwave to successfully initiate the main charge, as so full detonation occurs.
The most significant tertiary material in widespread general usage is ANFO, an explosive binary made from Ammonium nitrate and Fuel oil.