by accident

偶然

The discovery was a happy accident.

这个发现是机缘巧合的。

accident and emergency

(Brit.)denoting a hospital department concerned with the provision of immediate treatment to people who are seriously injured in an accident or who are suddenly taken seriously ill

(英)急诊室

an accident waiting to happen

(informal)a potentially disastrous situation, typically caused by negligent or faulty procedures

(非正式)（尤指由于疏忽大意或程序错误而造成的）隐患

accidents will happen in the best regulated famili

(proverb)however careful you try to be, it is inevitable that some unfortunate or unforeseen events will occur

(谚)家规再严，事端难免

problems like these should not occur, but accidents will happen.

这类问题不应出现，但保不定会有意外的。

without accident

safely

安全地

he was able to stop the train without accident.

他能安全地停住火车。