A Blasting Cap, sometimes referred to as a detonator, or simply a cap is a small device with a measured amount of primary explosive contained. They are used to detonate larger amounts of explosives, usually referred to as the main charge. Detonators generally have thick and heavy walls, as to increase the velocity of detonation (VoD) Some caps contain two explosives, a primary and a secondary explosive. These are referred to as compound caps.