One thing that playing with GNU Units has taught me is useful equivalences between various energy measures.

1 Hiroshima ~= 15.5 kiloton TNT ~= 18 GWh.

A large powerplant generates roughly 1 GW of electricity, so running for 18 hours is the equivalent of 1 Hiroshima.

(GNU units ... seems to have this predefined, along with 'davycrocket", "nagasaki", "fatman", "littleboy", "ivyking", "castlebravo", "tsarbomba", "b53bomb", "trinity", and "gadget".)

This also makes clear that it's not merely the amount of energy released, but the rate which matters. A powerplant running for three quarters of a day isn't tremendously destructive. A Little Boy type fission bomb exploding in a few microseconds ... is. Slowing your car from 100 kph to 0 over 10 seconds is a strong stop, doing that in 0.1 seconds is a fatal accident.

Typically, a 10x increase or decrease in scale or magnitude is transformative. By very rough averages, a human walks at ~5 kph, an automobile travels at 50 kph, a commercial airliner at 500 kph, a fighter aircraft at 5,000 kph, and a spacecraft at 50,000 kph.