• There is no warning. The population has not been evacuated nor sought
     shelter. Both measures could reduce casualties.

• The detonation takes place at night when most people are at their 
    residences. This corresponds to the available census data.

• There is clear weather, with visibility of 10 miles (16 km).

• No other cities are attacked, an assumption that allows for analyzing the
    extent of outside help that would be required, if it were available.