How long does it take for dry gangrene to become life threatening if untreated in foot?

Limited risk per se: Dry gangrene begins at the distal part of the limb due to ischemia (lack of blood supply) and often occurs in the toes and feet of elderly patients due to arteriosclerosis (from arterial occlusion). There is limited putrefaction and bacteria fail to survive. This is usually indicative of more generalized peripheral vascular disease and as such, the life expectancy of such patients is limited.

Seconds: Dry gangrene is dead tissue that can easily become infected and lead to life threatening sepsis and death. You should see a physician immediately to treat dry or wet gangrene.