Overpressure (or blast overpressure) is the pressure caused by a shock wave over and above normal atmospheric pressure. The shock wave may be caused by sonic boom or by explosion, and the resulting overpressure receives particular attention when measuring the effects of nuclear weapons or thermobaric bombs.
According to an article in the journal Toxicological Sciences ,
Blast overpressure (BOP), also known as high energy impulse noise, is a damaging outcome of explosive detonations and firing of weapons. Exposure to BOP shock waves alone results in injury predominantly to the hollow organ systems such as auditory, respiratory, and gastrointestinal systems. [1]
An EOD suit worn by bomb disposal experts can protect against the effects of BOP. [2] [3]
| Overpressure psi (kPa; bar) | Effect on buildings and people within |
|---|---|
| 1 (6.9; 0.069) |
|
| 2 (14; 0.14) |
|
| 3 (21; 0.21) |
|
| 5 (34; 0.34) |
|
| 10 (69; 0.69) |
|
| 20 (140; 1.4) |
|
The above table details the effects of overpressure on the human body in a building affected by a blast of overpressure waves, as clarified later in the journal.
The human body can survive relatively high blast overpressure without experiencing barotrauma. A 5 psi blast overpressure will rupture eardrums in about 1% of subjects, and a 45 psi overpressure will cause eardrum rupture in about 99% of all subjects. The threshold for lung damage occurs at about 15 psi blast overpressure. A 35-45 psi overpressure may cause 1% fatalities, and 55 to 65 psi overpressure may cause 99% fatalities. [3]
According to documents released by the United States Military Defense Technical Information Center (DTIC),
Human beings have about a 50:50 chance of surviving 500 psi, but will probably be severely injured at 70-100 psi. Exposed eardrums will be ruptured 50% of the time at 15 psi. However, a standing man will be blown away at about 10 f/s velocity by a shock of 25 psi peak pressure. [4]
Overpressure in an enclosed space is determined using "Weibull's formula": [5] [6]
where:
A thermobaric weapon, also called an aerosol bomb, or a vacuum bomb, is a type of explosive munition that works by dispersing an aerosol cloud of gas, liquid or powdered explosive. The fuel is usually a single compound, rather than a mixture of multiple molecules. Many types of thermobaric weapons can be fitted to hand-held launchers, and can also be launched from airplanes.
A bomb is an explosive weapon that uses the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy. Detonations inflict damage principally through ground- and atmosphere-transmitted mechanical stress, the impact and penetration of pressure-driven projectiles, pressure damage, and explosion-generated effects. Bombs have been utilized since the 11th century starting in East Asia.
The effects of a nuclear explosion on its immediate vicinity are typically much more destructive and multifaceted than those caused by conventional explosives. In most cases, the energy released from a nuclear weapon detonated within the lower atmosphere can be approximately divided into four basic categories:
A boiling liquid expanding vapor explosion is an explosion caused by the rupture of a vessel containing a pressurized liquid that is or has reached a temperature sufficiently higher than its boiling point at atmospheric pressure. Because the boiling point of a liquid rises with pressure, the contents of the pressurized vessel can remain a liquid as long as the vessel is intact. If the vessel's integrity is compromised, the loss of pressure drops the boiling point, which can cause the liquid to convert to gas expanding rapidly. BLEVEs are manifestations of explosive boiling.
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.
Operation Blowdown was an explosives test carried out in the Kutini-Payamu jungle of Australia's Cape York Peninsula in 1963, to simulate the effects of a nuclear weapon on tropical rainforest. It was conducted by the Australian Army, the Department of Supply, and the Defence Standards Laboratory with participation from the United Kingdom, Canada and United States. In addition, blast effects on military material, field fortifications, supply points, and foot and vehicle movement were examined in a rainforest environment.
Ronan Point was a 22-storey tower block in Canning Town in Newham, East London, that partially collapsed on 16 May 1968, only two months after it opened. A gas explosion blew out some load-bearing walls, causing the collapse of one entire corner of the building; four people died and 17 were injured. The nature of the failure led to a loss of public confidence in high-rise residential buildings, and major changes in British building regulations resulted.
A blast shelter is a place where people can go to protect themselves from blasts and explosions, like those from bombs, or in hazardous worksites, such as on oil and gas refineries or petrochemical facilities. It differs from a fallout shelter, in that its main purpose is to protect from shock waves and overpressure instead of from radioactive precipitation, as a fallout shelter does. It is also possible for a shelter to protect from both blasts and fallout.
The explosive yield of a nuclear weapon is the amount of energy released such as blast, thermal, and nuclear radiation, when that particular nuclear weapon is detonated, usually expressed as a TNT equivalent (the standardized equivalent mass of trinitrotoluene which, if detonated, would produce the same energy discharge), either in kilotonnes (kt—thousands of tonnes of TNT), in megatonnes (Mt—millions of tonnes of TNT), or sometimes in terajoules (TJ). An explosive yield of one terajoule is equal to 0.239 kilotonnes of TNT. Because the accuracy of any measurement of the energy released by TNT has always been problematic, the conventional definition is that one kilotonne of TNT is held simply to be equivalent to 1012 calories.
A nuclear explosion is an explosion that occurs as a result of the rapid release of energy from a high-speed nuclear reaction. The driving reaction may be nuclear fission or nuclear fusion or a multi-stage cascading combination of the two, though to date all fusion-based weapons have used a fission device to initiate fusion, and a pure fusion weapon remains a hypothetical device. Nuclear explosions are used in nuclear weapons and nuclear testing.
Explosives safety refers to the practices taken during the use of explosives to prevent injury or death. Explosives include chemicals such as TNT or dynamite.
In fluid dynamics, a blast wave is the increased pressure and flow resulting from the deposition of a large amount of energy in a small, very localised volume. The flow field can be approximated as a lead shock wave, followed by a similar subsonic flow field. In simpler terms, a blast wave is an area of pressure expanding supersonically outward from an explosive core. It has a leading shock front of compressed gases. The blast wave is followed by a blast wind of negative gauge pressure, which sucks items back in towards the center. The blast wave is harmful especially to objects very close to the center or at a location of constructive interference. High explosives that detonate generate blast waves.
An underwater explosion is a chemical or nuclear explosion that occurs under the surface of a body of water. While useful in anti-ship and submarine warfare, underwater bombs are not as effective against coastal facilities.
A bomb suit, Explosive Ordnance Disposal (EOD) suit or a blast suit is a heavy suit of body armor designed to withstand the pressure generated by a bomb and any fragments the bomb may produce. It is usually worn by trained personnel attempting bomb disposal. In contrast to ballistic body armors, which usually focus on protecting the torso and head, a bomb suit must protect all parts of the body, since the dangers posed by a bomb's explosion affect the entire body.
A muzzle blast is an explosive shockwave created at the muzzle of a firearm during shooting. Before a projectile leaves the gun barrel, it obturates the bore and "plugs up" the pressurized gaseous products of the propellant combustion behind it, essentially containing the gases within a closed system as a neutral element in the overall momentum of the system's physics. However, when the projectile exits the barrel, this functional seal is removed and the highly energetic bore gases are suddenly free to exit the muzzle and rapidly expand in the form of a supersonic shockwave, thus creating the muzzle blast.
Operation Sailor Hat was a series of explosives effects tests, conducted by the United States Navy Bureau of Ships under the sponsorship of the Defense Atomic Support Agency. The tests consisted of two underwater explosions at San Clemente Island, California in 1964 and three surface explosions at Kahoʻolawe, Hawaii in 1965. They were non-nuclear tests employing large quantities of conventional explosives to determine the effects of a nuclear weapon blast on naval vessels, and the first major test of this kind since Operation Crossroads in July 1946.
An explosion is a rapid expansion in volume of a given amount of matter associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Explosions may also be generated by a slower expansion that would normally not be forceful, but is not allowed to expand, so that when whatever is containing the expansion is broken by the pressure that builds as the matter inside tries to expand, the matter expands forcefully. An example of this is a volcanic eruption created by the expansion of magma in a magma chamber as it rises to the surface. Supersonic explosions created by high explosives are known as detonations and travel through shock waves. Subsonic explosions are created by low explosives through a slower combustion process known as deflagration.
The Advanced Bomb Suit (ABS) is a full body bomb suit designed to protect explosive ordnance disposal (EOD) soldiers from threats associated with improvised explosive devices, including those related to fragmentation, blast overpressure, impact, heat, and flame. Manufactured by Med-Eng, the ABS uses new material technology and design to improve protection, comfort, and ergonomics. The suit is constructed from Kevlar with an outer anti-static cover of 50/50 Nomex/Kevlar and comprises a jacket, crotchless trousers, groin cup, and rigid ballistic panels. To minimize weight and maximize flexibility, protection is provided at various levels, specific to body regions, based on susceptibility to wounds. The suit does not provide gloves to the operator so that maximum ability on the hands is present.
Blast-related ocular trauma comprises a specialized subgroup blast injuries which cause penetrating and blunt force injuries to the eye and its structure. The incidence of ocular trauma due to blast forces has increased dramatically with the introduction of new explosives technology into modern warfare. The availability of these volatile materials, coupled with the tactics of contemporary terrorism, has caused a rise in the number of homemade bombs capable of extreme physical harm.
Middle ear barotrauma (MEBT), also known to underwater divers as ear squeeze and reverse ear squeeze, is an injury caused by a difference in pressure between the external ear canal and the middle ear. It is common in underwater divers and usually occurs when the diver does not equalise sufficiently during descent or, less commonly, on ascent. Failure to equalise may be due to inexperience or eustachian tube dysfunction, which can have many possible causes. Unequalised ambient pressure increase during descent causes a pressure imbalance between the middle ear air space and the external auditory canal over the eardrum, referred to by divers as ear squeeze, causing inward stretching, serous effusion and haemorrhage, and eventual rupture. During ascent internal over-pressure is normally passively released through the eustachian tube, but if this does not happen the volume expansion of middle ear gas will cause outward bulging, stretching and eventual rupture of the eardrum known to divers as reverse ear squeeze. This damage causes local pain and hearing loss. Tympanic rupture during a dive can allow water into the middle ear, which can cause severe vertigo from caloric stimulation. This may cause nausea and vomiting underwater, which has a high risk of aspiration of vomit or water, with possibly fatal consequences.
