There are mainly 3 factors which seems to take effect on the rush accident rate:

The summed amount of stats. For example the Reactor: I have one reactor with 3 People inside it, all have around S:3. It has a higher accident rate than a room with just one Person in it with S:10, but the same accident rate as a Person with S:9. This leads me to the conclusion, that the right stat in sum(!) will take effect on the accident rate. Beside the correct stat for a room (S:Reactor, P:Water, A:Dinner,...) the L factor takes effect. Just like in the real fallout games too. L will always improve percentage values. In this case I have a room with same needed stats (S:9 for example), one with L:2 one with L:8 (maybe due to more people in it). The room with higher L has a accident rate of 14 as the other room has a accident rate of 19 percent. The time! If you rush a room too often in a too short range of time, the accident rate will grow. On rooms with a good stuffing (high stats which are needed + luck) your able to rush 1-3 times before it will get to a "critical" accident rate of 30%. After a few collections it's back to its original accident rate of 10%.

Hopefully this will help you.