The number and type of fatalities and injuries depend on many factors including the yield of the nuclear device, the population near the site of the explosion and in the fallout path, and weather conditions. Even a partial nuclear detonation could produce many casualties in a densely populated area. An extensive weapons effects testing program and studies of the 1945 bombings of Hiroshima and Nagasaki provide what we know about the effects of nuclear explosions.
Health Effects from the Shockwave and Thermal Energy
Fatalities and injuries will result from the pressure of the shockwave, bodies being thrown, falling buildings, and flying debris. Thermal (heat) energy including the fireball can cause fatalities and severe burns to the skin and eyes.
Health Effects from Radiation
People who survive the physical shockwave and heat may suffer health effects from radiation. The health effects of radiation depend on the:
- Amount of radiation absorbed by the body (the dose, measured in unit called rads)
- Type of radiation
- Route of exposure (absorbed by the body, inhaled, or ingested)
- Length of time exposed
If a reasonable estimate can be made of a person's dose, health effects at that dose can be predicted with good accuracy. There are both short- and long-term effects of radiation.
Acute Radiation Syndrome (ARS) may develop in those who are exposed to radiation levels of 50-100 rad, depending on the type of radiation and the individual. Symptoms of ARS include nausea,vomiting, diarrhea, and reduced blood cell counts. Radiation, especially beta radiation, can also cause skin burns and localized injury. Fatalities begin to appear at exposures of 125 rad, and at doses between 300-400 rad, about half of those exposed will die without supportive treatment. At very high doses, greater than 1000 rad, people can die within hours or days due to effects on the central nervous system. Radiation exposure inhibits stem-cell growth; for those who die within weeks to months, death is usually caused by damage to the gastrointestinal lining and to bone marrow where stem cell growth is crucial. Fetuses are more sensitive to radiation; effects may include growth retardation, malformations, or impaired brain function.
Radiation exposure increases the risk of developing cancer, including leukemia, later in life. The increased cancer risk is proportional to radiation dose. The survivors of the Hiroshima and Nagasaki atomic bombs have about a 10% increased risk of developing cancers over normal age-specific rates, some occurring more than 50 years following the exposure. A long-term medical surveillance program would likely be established to monitor potential health effects of survivors of a nuclear attack. There is no evidence of genetic changes in survivors' children who were conceived and born after the bombings in Hiroshima and Nagasaki.