Overpressure

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, 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.

An EOD suit worn by bomb disposal experts can protect against the effects of BOP.

Overpressure psi	Effect on buildings and people within
	Window glass shatters Light injuries from fragments occur
	Moderate damage to houses People injured by flying glass and debris
	Residential structures collapse Serious injuries are common, fatalities may occur
	Most buildings collapse except reinforced concrete buildings Injuries are universal, fatalities are widespread
	Reinforced concrete buildings severely damaged or demolished Most people are killed
	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.
According to documents released by the United States Military Defense Technical Information Center,
It is important to note that this is for "Instantaneous peak pressure" while the preceding table is for long duration pressure.

Calculation for an enclosed space

Overpressure in an enclosed space is determined using "Weibull's formula":
where:

22.5 is a constant based on experimentation
= net explosive mass calculated using all explosive materials and their relative effectiveness
= volume of given area