Overpressure

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]

Overpressure	Effects[3]
10 pounds per square inch (69 kPa)	Reinforced concrete buildings severely damaged Severe heart and lung damage Limbs can be blown off
4 pounds per square inch (28 kPa)	Most buildings collapse except concrete buildings Injuries universal Fatalities occur
2 pounds per square inch (14 kPa)	Residential structures collapse Brick walls destroyed Injuries common Fatalities may occur

Calculation for an enclosed space

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

${\displaystyle \Delta p=22.5\left({m \over V}\right)^{0.72}{\text{bars}}}$

where:

• 22.5 is a constant based on experimentation
• ${\displaystyle m\,}$ = (kilograms) net explosive mass calculated using all explosive materials and their relative effectiveness
• ${\displaystyle V\,}$ = (cubic meters) volume of given area (primarily used to determine volume within an enclosed space)

See also

• Bomb disposal

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. Pavlus, John (March 4, 2010). "Real-life Hurt Locker: how bomb-proof suits work".
3. Fool Me Twice (documentary film). Retrieved January 26, 2015.
4. Hans R. W. Weibull (October 1968) "Pressures recorded in partially closed chambers at explosion of TNT charges" Annals of the New York Academy of Sciences 152 (1) : 357-361.
5. "Laboratory barricade".