There is no clear limit to how much oxygen saturation is below which will lead to sudden death, but if oxygen saturation is below 70% for a long period of time, it will be life-threatening.
Oxygen saturation is an important indicator to reflect whether the body is hypoxic or not, under normal circumstances, the oxygen saturation of arterial blood is greater than 95%, if the oxygen saturation is lower than 70% for a long time, and no timely treatment, no correction of hypoxia, then it may cause multiple organ failure and life-threatening.
If the oxygen saturation level is below 50% or even lower for a short period of time, but if rescue is timely and hypoxia is corrected, the risk to life can be reduced. If the oxygen saturation level is lower than normal, you should seek medical attention to correct the hypoxia.