Which SC2 units can accidentally cause friendly fire?
Solution 1:
The only units that actually cause friendly fire from splash damage are:
- Siege tank shells
- Psionic storms
- Widow Mine attacks (except for other widow mines)
- Raven's Seeker Missiles
- Ghost's EMP
- Ghost's Tactical Nuke
Some units that you might expect to cause FF splash damage but in fact don't are:
- Yamato cannon on BCs (doesn't cause any splash)
- Planetary Fortresses
- Hellion/Hellbat attacks
- Thor attacks
- Baneling explosions
- Infestor's fungal growth
- Ultralisk attacks
- Mutalisk attacks
- Colossi attacks
- Archon attacks
Edit: See this website for more details.
Solution 2:
Currently the units which can cause friendly fire are Siege Tanks (in siege mode), Psionic Storms, Widow Mines, and Raven's Seeker Missiles.