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.
No correlation between time remaining and rush failure percentage
The in-game help mentions that the probability of a rush failure decays over time. Attempting a rush, whether it succeeds or fails, will increase the probability of a rush failure in that room, but this is a one time increase and it starts to decay again after that. There also seems to be a lower limit on rush failure. likely based on Luck and the appropriate SPECIAL stat for the room. The lowest I've seen is 21% failure chance on a room that I haven't rushed in days. James reported seeing as low as 16% with a maxed out, very lucky water treatment plant.
In my experience, the failure decay rate is so small that you probably would not notice it over a few minutes (the normal task completion time for a well populated room), but it becomes noticeable over a few hours. After spiking the failure chance in a room to around 50% right before bed, I woke up the next morning with the failure chance back down to upper 20s/lower 30s. This seems to indicate that it is based on elapsed time rather than decaying after a room is harvested.
When you couple this with the fact that the timer is reset to max after a rush is attempted, rushing a room with a few seconds left is not as resource effective as harvesting the resources, then attempting the rush when the timer is full. In that case, you save a lot of time if you succeed and don't lose as much time if you fail.
tl;dr
It seems to be a percentage calculated when you click the rush button, regardless of how much time is left until the room produces resources. Rush failure percentage chances slowly decrease over time, but this is noticeable over tens of minutes and hours, rather than seconds. If you want to maximize the amount of time your rush saves, rush right after you collect, when the room timer has a lot of time left.
Best Answer
I had a "slowpoke" medic (the one producing medpacks) with operation cycle over
10 min. I've noticed, what after it produces stimpack on its own - he is back to34%(minimum incident chance for him).So it's about
10 %every10 mindecrease. Assuming you are always keeping it at minimum.In other words rush everything, exit game, wait 10 min, start game, rush everything, repeat for maximizing money income (without risk to fall into incidents/attacks in between).