accidental

The fire was ruled as accidental, caused by an old electrical wire in the attic.

(Chinese) 火灾被裁定为意外，是由阁楼里的一根旧电线引起的。

The discovery of the ancient ruins was accidental; workers were just digging a well.

(Chinese) 发现古代遗址纯属偶然；工人们当时只是在挖一口井。