Basic function for when an object looses it's health?

I am making a statue currently with a humanoid, and if it's health reaches zero, the main part named "Statue" turns invisible, and then "fragments" of the statue become visible which were invisible before. If anyone can help me on this, and or write the code for me (I can write the code, I just need the function, and I'll come back later if it doesn't work.) Also, the code will be in the model itself.