|The following is based on Fallout Shelter or Fallout Shelter Online and some details might contradict canon.|
Incidents are a mechanic found in Fallout Shelter. It can happen randomly, or when rushing a room fails. Incidents need to be dealt with quickly by dwellers or they will spread to adjacent rooms. During an incident, dwellers in the same room are damaged and will not produce anything until the incident has been resolved. Possible incidents include radroach, mole rat and radscorpion infestations, fires, and raider, feral ghoul or deathclaw attacks.
- Mole rat incidents will start in rooms touching dirt, including the "stone" on the edge of the build area.
- Raider, feral ghoul and deathclaw attacks cannot be caused by failing to rush a room, but will instead happen randomly.
- Deathclaw attacks appear to be much rarer than raider attacks.
- Difficulty of the incident depends on the size and the level of the room it starts in.
- Radscorpion and feral ghoul attacks start appearing at vault population of 50+.
- Deathclaw attacks start appearing when the vault has 60+ dwellers.
- Attacks by deathclaws, raiders and feral ghouls become more frequent as the vault expands.
- Occasionally, a raider, feral ghoul or deathclaw attack will happen immediately after sending a dweller on a quest or to explore the wasteland.