意外

The news of the accident came as a bolt from the blue. / The news went down like a bomb. / The news was a complete thunderbolt.

The gun went off by accident.

pleasant surprise

unforeseen trouble

suffer an unexpected defeat

accidental explosion

give sb a big surprise

be taken by surprise

This is a pure accident.

Don't try to escape your obligation by claiming accident.

bring about/cause an accident

suffer a mishap

meet with/have a mishap; meet with/have an accident

cut down/reduce accidents

prevent accidents

an accident happens/befalls; a mishap befalls

avoid accidents/mishaps