Outline of Atomic Bomb Damage

  Hiroshima    Nagasaki
Time of Explosion  8:15 a.m.Augus 6, 1945 11:02 a.m.August 9, 1945
Number of deadAs of the end ofDecember(Estimated) Approx. 140.000(People in the city at thetime about: 350.000) Approx 74.000(People in the city at thetime: about 240.000)

Primary Charactaristics of the Damage

1. Massive destruction

Nuclear fission generates enormous energy, incomparably greater than that of conventional weapons, resulting in massive, far-reaching destruction and slaughter brought about by the synergistic effects of powerful heat rays, blast force, and radiation.

2. Instant and Indiscriminate Destruction

The atomic bombs caused massive, instantaneous destruction of property and the indiscriminate mass slaughter of military personnel, civilians, women, children, and the elderly.

3. Long-term Damage

In addition to losing family members, neighbors, and their socioeconomic foundations, including their workplaces, survivors have been forced to struggle continuously with the effects of radiation. They have been forced to live with the fear that a radiation-induced disease could attack them at any time.

Breakdown of A-bomb Energy Released

Of the energy emitted by the explosion, approximately 50% was released as blast force, 35% as heat rays, and 15% as radiation (initial radiation: 5%, residual radiation: 10%).

Damage to Buildings (Hiroshima)

Because the atomic bomb exploded close to the city center and 85% of the buildings in the city stood within 3 km (1.8 miles) of the hypocenter, the entire city was damaged. Over 90% of Hiroshima’s buildings were burned or collapsed.

Damage to Buildings (Nagasaki)

All buildings within 1 km (0.6 miles) of the hypocenter collapsed completely, and wooden houses and buildings within 4 km (2.4 miles) of the hypocenter were at least partially collapsed. One third of the city was totally burned by fires that broke out everywhere.

Damage due to Heat Rays

When the atomic bomb exploded, the temperature at the epicenter soared to over one million degrees centigrade. In one second, the fireball expanded to 306 yards (280 m) in diameter. The heat rays emitted in all directions by the fireball brought temperatures on the ground near the hypocenter to 3,000 to 4,000°C (5,432 to 7,232°F). [Iron melts at 1,536°C (2,797°F)]

Damage due to blast

A super-high pressure of several hundred thousand atmospheres was created at the epicenter of the atomic explosion. The surrounding air expanded enormously, generating a shock wave followed by a powerful blast wind. At the hypocenter, maximum blast pressure was 35 tons per square meter and maximum wind velocity was 440 m/sec (about 1,000 mph). The shock wave and blast crushed nearly all wooden buildings within approximately 1.2 miles (2 km) of the hypocenter. Close to the hypocenter it crushed even steel-reinforced concrete buildings.

Damage due to Super-High-Temperature Fires

When the atomic bomb exploded, intense heat rays ignited houses and anything combustible near the hypocenter. In collapsed houses everywhere, kitchen fires spread quickly out of control. The conflagration spread throughout the entire city and burned intensely into the night. In Hiroshima approximately 8 square miles (13 square kilometers) were burned to the ground. In Nagasaki, approximately 4.2 square miles (6.7 square kilometers). The burned area was larger in Hiroshima because of differences in terrain and the distribution of buildings.

Damage to Human Bodies

The symptoms inflicted by the A-bomb are broadly divided into acute disorders and aftereffects. Most acute disorders were caused by complex interactions of heat rays and fire burns, blast contusions, lacerations, and radiation damage. They subsided within four to five months after the bombing.

“Aftereffects” refers to symptoms that manifested after the acute disorders healed. Most are assumed to be the result of radiation.

− Due to Heat Rays and Fire

Those directly exposed to heat rays within 0.7 miles (1.2 km) of the hypocenter were burned through the skin and into the tissues below. Internal organs were damaged. The vast majority died immediately or within a few days.  Nearly every building in the city collapsed, trapping thousands under the debris. Unable to free themselves, they burned to death in the sea of fire ignited by the bomb.

A-bomb Blast Injuries

The blast hurled thousand of people through the air. Skin burned by the heat rays was peeled off and dangled in strips. Glass windows were shattered, and many victims were left with hundreds of glass fragments lodged in their bodies.

Damage due to Radiation

− Acute Symptoms

Penetrating deeply into the bodies of victims, radiation damaged cells, diminished the blood generation function of bone marrow, damaged the lungs, liver, and other organs, and inflicted other grave damage. The initial radiation emitted within a minute of the explosion was lethal as far as 0.6 miles (1 km) from the hypocenter. Most in that area died in a few days. Many who appeared uninjured developed disorders and died days or months later. Thousands who entered the city to participate in relief activities developed symptoms similar to those resulting from direct exposure. Many died. The immediate effects of radiation poisoning include the destruction of cells, damage to blood-forming and other organs, weakened immune functions, and loss of hair.


Most acute injuries either killed victims or healed in 4 to 5 months. The aftereffects, including an obvious increase in leukemia 5 to 6 years after the bombing, have continued to cause serious problems. The most common aftereffects include keloids (abnormally thick scar tissue), cataracts, and leukemia, as well as thyroid, breast, lung, and other cancers. Some in-utero survivors were born with microcephaly, an abnormal smallness of the head, often accompanied by mental and developmental disorders. We still have much to learn about the effects over the years of radioactive substances taken into the body. We do know that survivors continue to suffer from the aftereffects of radiation.

Malignant Neoplasms

Cancers observed and the approximate dates at which significant increases became evident: leukemia (1950); thyroid cancer (1955); breast and lung cancer (1965); multiple myelomas, gastric and colon cancer (1975). Radiation is a proven causal factor. In some cases, researchers have reported a direct correlation between distance from the hypocenter or probable radiation absorbed and malignancy rates.

In-utero Exposure

The atomic bomb affected fetuses in-utero. Many died before birth, but those born without obvious problems also had a higher death rate. Some in-utero survivors exposed close to the hypocenter and in early pregnancy were born with abnormally small heads. This condition, called microcephaly, is often accompanied by levels of cognitive disorders that make its victims unable to manage everyday life without assistance.