how many categories of struck-by hazards are there?

There are four categories of struck-by hazards in OSHA construction safety:

• Struck-by flying object
• Struck-by falling object
• Struck-by swinging object
• Struck-by rolling object

OSHA training materials and safety programs consistently define these four as the core struck‑by hazard categories used in construction and general workplace safety education.

In simple terms: if something hits you because it’s flying, falling, swinging, or rolling, it fits into one of these four struck‑by hazard categories.

TL;DR: If you see a multiple-choice question asking “how many categories of struck‑by hazards are there?”, the best answer is 4.

Information gathered from public forums or data available on the internet and portrayed here.