Rushing rooms is a key mechanic in Fallout Shelter that allows you to instantly produce resources, bottle caps, and experience points for the dwellers stationed there. However, rushing a room will not always have a positive outcome. Each time you rush a room, the chance of an incident such as a Radroach Infestation or Fire breaking out is increased by 10%. This can be disastrous later in the game when Molerat Infestations and Radscorpion Infestations can occur. However, you can lower the chance of an incident by merging a room, allowing you to Rush a room with minimal danger. You can do this twice to a room until it's merged into a triple room. If you use this method, make sure to swap out any spare vault dwellers for unhappy vault dwellers, as unhappy dwellers will reduce the amount of production and increase the chance of an incident occurring. Improving your dweller's S.P.E.C.I.A.L Stats is another way to reduce the risk of an incident in a room. For example, level your dweller's Perception and Luck stats if you want to rush to a Water Treatment room. Luck will increase your chances of a successful rush. Therefore, I suggest equipping your dwellers with any spare clothing that increases Luck, like the common Formal Wear apparel.