Effects of Blast

With the explosion an exceedingly high pressure of several hundred thousand millibars developed at the burst point and the surrounding air expanded greatly and created a blast. The front of the blast advanced as a shock wave (a wall of high pressure air) at a speed greater than or equivalent to that of sound. A flow of air generally at subsonic speed followed the shock wave after it passed and spread outward. The shock wave, one second after detonation, advanced 1 80 meters in front of the fireball when it spread to its maximum diameter of 280 meters. Approximately 10 seconds after the explosion, the shock wave reached a point about 3.7 kilometers from the burst point.
In the hypocenter the maximum blast pressure was 35 tons/rn 2 maximum velocity was 440 meters/sec. Even at- 3 kilometers from the hypocenter maximum blast pressure was 1.3 tons/m² : maximum velocity was 30 meters/sec.

(1) Humandamage

a. Those on the streets were blown off the ground for several meters. Those indoors were also blown away.
b.Uncountable number of people were burnt to death, trapped in buildings blown down by the blast.
c.Clothes were stripped off and burnt skin was torn off in rags.
d. A great number of people were injured by broken glass fragments, which penetrated deeply into their bodies.
e. There were, fortunately, not so many people who had visceral cleft, bleed mg or fracture of bone.

(2) Damage done to buildings

Wooden houses a. Those within a radius of 2.3 kilometers were almost totally obliterated. b. Those within a radius of 2.6 kilometers were damaged beyond repair. c. Those within a radius of 3.2 kilometers were partially damaged, usable if repaired, but with all the household       fittings blown away, and roof-tiles sliding, which caused leaks in roofs.
d.Damage on household fittings was seen to the distance of 6 kilometers; roof-tiles sliding, ~ kilometers; and breaking or cracking of glass, 16 kilo-	The main building of a temple at Onaga-cho. (3,350 meters from the hypocenter. Photographed by Shunkichi Kikuchi.)

Concrete buildings

Those around the hypocenter were severely damaged with the top ceiling crashing down,        windows and doors      as well as their frames totally blown away, and all the other fittings smashed and scattered. Those outside a radius of I kilometer endured the blast, but the interiors were left to the menace  of raging fires.
To the distance of 2 kilometers, all the windows were blown away, and those which faced to the direction of    the hypocenter were completely blown away together with their frames.	Hiroshima Gas Co. Building at Otemachi destroyed by the strong blast pressure. (Approximately 250 meters from the hypocenter. Photographed by Shigeo Hayashi.)