Overpressure Explained

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.

Effects

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
1psi	Window glass shatters Light injuries from fragments occur
	2psi	Moderate damage to houses (windows and doors blown out and severe damage to roofs) People injured by flying glass and debris
	3psi	Residential structures collapse Serious injuries are common, fatalities may occur
	5psi	Most buildings collapse except concrete buildings Injuries are universal, fatalities are widespread
	10psi	Reinforced concrete buildings severely damaged or demolished Most people are killed
	20psi	Heavily built concrete buildings are severely damaged or demolished Fatalities approach 100%

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.

According to documents released by the United States Military Defense Technical Information Center (DTIC),

Calculation for an enclosed space

Overpressure in an enclosed space is determined using "Weibull's formula":^{[4] [5]}

where:

• 22.5 is a constant based on experimentation

= (kilograms) net explosive mass calculated using all explosive materials and their relative effectiveness = (cubic meters) volume of given area (primarily used to determine volume within an enclosed space)

See also

• Bomb disposal

Notes and References

1. "Pulmonary Biochemical and Histological Alterations after Repeated Low-Level Blast Overpressure Exposures",Nabil M. Elsayed, and Nikolai V. Gorbunov, Toxicological Sciences, 2007 95(1):289-296, online version 2006, http://toxsci.oxfordjournals.org/cgi/content/abstract/95/1/289
2. Web site: Real-life Hurt Locker: how bomb-proof suits work . John . Pavlus . March 4, 2010 .
3. Web site: Effects of blast pressure on the human body.
4. 10.1111/j.1749-6632.1968.tb11987.x . Pressures Recorded in Partially Closed Chambers at Explosion of TNT Charges . 1968 . Weibull . Hans R. W. . Annals of the New York Academy of Sciences . 152 . 1 . 357–361 . 1968NYASA.152..357W . 84258773 .
5. US. 4474052. Bodurtha Jr. . Frank T. . Bonifaz . Cristobal. Laboratory barricade. October 2, 1984. patent.