A blast injury is a complex type of physical trauma resulting from direct or indirect exposure to an explosion. Blast injuries occur with the detonation of high-order explosives as well as the deflagration of low order explosives. These injuries are compounded when the explosion occurs in a confined space. Classification Blast injuries are divided into four classes: primary, secondary, tertiary, and quaternary. Primary injuries Primary injuries are caused by blast overpressure waves, or shock waves. Total body disruption is the most severe and invariably fatal primary injury. Primary injuries are especially likely when a person is close to an exploding munition, such as a land mine. The ears are most often affected by the overpressure, followed by the lungs and the hollow organs of the gastrointestinal tract. Gastrointestinal injuries may present after a delay of hours or even days. Injury from blast overpressure is a pressure and time dependent function. By increasing the pressure or its duration, the severity of injury will also increase. Extensive damage can also be inflicted upon the auditory system. The tympanic membrane (also known as the eardrum) may be perforated by the intensity of the pressure waves. Furthermore, the hair cells, the sound receptors found within the cochlea, can be permanently damaged and can result in a hearing loss of a mild to profound degree. Additionally, the intensity of the pressure changes from the blast can cause injury to the blood vessels and neural pathways within the auditory system. Therefore, affected individuals can have auditory processing deficits while having normal hearing thresholds. The combination of these effects can lead to hearing loss, tinnitus, headache, vertigo (dizziness), and difficulty processing sound. In general, primary blast injuries are characterized by the absence of external injuries; thus internal injuries are frequently unrecognized and their severity underestimated. According to the latest experimental results, the extent and types of primary blast-induced injuries depend not only on the peak of the overpressure, but also other parameters such as number of overpressure peaks, time-lag between overpressure peaks, characteristics of the shear fronts between overpressure peaks, frequency resonance, and electromagnetic pulse, among others. There is general agreement that spalling, implosion, inertia, and pressure differentials are the main mechanisms involved in the pathogenesis of primary blast injuries. Thus, the majority of prior research focused on the mechanisms of blast injuries within gas-containing organs and organ systems such as the lungs, while primary blast-induced traumatic