– Ball of fire –
The first thing people noticed was an “intense ball of fire” according to the International Committee of the Red Cross (ICRC).
The atomic bomb had a yield of 15 kilotonnes, equal to 15,000 tonnes of TNT, yet was 3,300 times less powerful than the biggest hydrogen bomb tested by the Soviet Union in 1961.
Temperatures at the epicentre of the blast reached an estimated 7,000 degrees Celsius (12,600 Fahrenheit), which caused fatal burns within a radius of about three kilometres (five miles).
ICRC experts say there were cases of temporary or permanent blindness due to the intense flash of light, and subsequent related damage such as cataracts.
A whirlwind of heat generated by the explosion also ignited thousands of fires that burned several square kilometres (miles) of the largely wooden city. A firestorm that consumed all available oxygen caused more deaths by suffocation.
It has been estimated that burn- and fire-related casualties accounted for more than half of the immediate deaths in Hiroshima.
– Shock wave –
The explosion generated an enormous shock wave and almost instantaneous expansion of air which also caused a huge number of deaths.
Some people were literally blown away while others were crushed inside collapsed buildings or perforated by flying debris.
The ICRC recorded many victims with ruptured internal organs, open fractures, broken skulls and penetration wounds.
– Radiation –
Another deadly effect of the atomic bomb was the emission of radiation that proved harmful in both the short and long term.
Radiation sickness was reported in the attack’s aftermath by many who survived the initial blast and firestorm.
Acute radiation symptoms include vomiting, headaches, nausea, diarrhoea, haemorrhaging and hair loss. Radiation sickness can lead to death within a few weeks or months.
Longer-term effects noted among “hibakusha”, or bomb survivors, are increased risks of thyroid cancer or leukaemia.
In both Hiroshima and Nagasaki, which was hit by an atomic bomb on August 9, 1945, the rate of various cancers and leukaemia have risen.
Of 50,000 radiation victims from both cities studied by the Japanese-US Radiation Effects Research Foundation, about 100 died of leukaemia and 850 suffered from radiation-induced cancers.
The foundation found no evidence of a “significant increase” in serious birth defects among survivors’ children, however.