Editing Overpressure

{{Short description|Pressure due to a shockwave}}
{{about|shock waves in the atmosphere}}
'''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 weapon]]s or [[thermobaric bomb]]s.

== Effects ==

According to an article in the journal ''[[Toxicological Sciences]]'',

<blockquote>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.<ref>"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</ref></blockquote>

An [[bomb suit|EOD suit]] worn by [[bomb disposal]] experts can protect against the effects of BOP.<ref>{{Cite web |title=Real-life Hurt Locker: how bomb-proof suits work |first=John |last=Pavlus |date=March 4, 2010 |url=http://dvice.com/archives/2010/03/hurt-locker-sui.php}}</ref><ref name=EOB>{{cite web |url=https://www.cdc.gov/niosh/docket/archive/pdfs/niosh-125/125-explosionsandrefugechambers.pdf|title=Effects of blast pressure on the human body}}</ref>

{| class="wikitable"
|-
! Overpressure<br /> [[Pound per square inch|psi]] ([[kPa]]; [[bar (unit)|bar]])
! Effect on buildings and people within
|-
| {{convert|1|psi|kPa bar|abbr=values}}
|
* Window glass shatters
* Light injuries from fragments occur
|-
| | {{convert|2|psi|kPa bar|abbr=values}}
|
* Moderate damage to houses (windows and doors blown out and severe damage to roofs)
* People injured by flying glass and debris
|-
| | {{convert|3|psi|kPa bar|abbr=values}}
|
* Residential structures collapse
* Serious injuries are common, fatalities may occur
|-
| | {{convert|5|psi|kPa bar|abbr=values}}
|
* Most buildings collapse except reinforced concrete buildings
* Injuries are universal, fatalities are widespread
|-
| | {{convert|10|psi|kPa bar|abbr=values}}
|
* Reinforced concrete buildings severely damaged or demolished
* Most people are killed
|-
| | {{convert|20|psi|kPa bar|abbr=values}}
|
* Heavily built reinforced 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. {{quote|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.<ref name=EOB/>}}

According to documents released by the United States Military [[Defense Technical Information Center]] (DTIC),
{{quote|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.<ref>{{cite web |url=https://apps.dtic.mil/sti/tr/pdf/AD0067365.pdf|title=Blast Effects of Bomb Explosives}}</ref>}}

== Calculation for an enclosed space ==
Overpressure in an enclosed space is determined using "Weibull's formula":<ref>{{cite journal|doi=10.1111/j.1749-6632.1968.tb11987.x |title=Pressures Recorded in Partially Closed Chambers at Explosion of TNT Charges |year=1968 |last1=Weibull |first1=Hans R. W. |journal=Annals of the New York Academy of Sciences |volume=152 |issue=1 |pages=357–361 |bibcode=1968NYASA.152..357W |s2cid=84258773 }}</ref><ref>{{Cite patent |country=US|number=4474052|invent1=Bodurtha Jr. |inventor1-first=Frank T. |invent2=Bonifaz |inventor2-first=Cristobal|url=http://www.freepatentsonline.com/4474052.html | title=Laboratory barricade|gdate=October 2, 1984|status=patent}}</ref>

<math>\Delta p = 22.5 \left( {m \over V} \right)^{0.72} \text{bars}</math>

where:
*22.5 is a constant based on experimentation
*<math>m\,</math> = (kilograms) [[net explosive mass]] calculated using all explosive materials and their relative effectiveness
*<math>V\,</math> = (cubic meters) volume of given area (primarily used to determine volume within an enclosed space)

== See also ==
*[[Bomb disposal]]

== References ==
{{Reflist}}

[[Category:Pressure]]
[[Category:Explosives]]
[[Category:Shock waves]]