The correct sentence is option two:
There have been many accidents during airshows; for example, last year the wind toppled a tent and equipment on top of bystanders.
The semicolon is a punctuation mark which indicates a pause, usually between two clauses that are not joined by a coordinating conjunction. Semicolons can also replace commas to separate elements in a list that already includes commas.
In the example sentence, the semicolon separates two clauses. Besides, a comma follows the introductory phrase "for example" because it introduces a clause.
