Brain death following SN ingestion is secondary to hypoxia caused by severe methemoglobinemia. Once methemoglobin levels exceed approximately 70–80%, oxygen delivery to tissues—including the brain—is critically impaired.
Loss of consciousness typically occurs within 20 to 40 minutes after ingestion (sometimes sooner depending on dose, individual physiology, and presence of antiemetics), due to hypoxic effects on the central nervous system.
As for complete brain death, the data is less precise. From existing case reports and forensic literature, irreversible brain damage can begin within 4–6 minutes of sustained anoxia, but full clinical brain death (cessation of all brain activity) is generally thought to occur between 20 and 40 minutes of continuous critical hypoxia—assuming no medical intervention and continued progression of oxygen deprivation.
Because the heart may continue to beat for a time after consciousness is lost, brain death often lags behind cardiac arrest. However, in fatal SN cases without reversal, the timeline from ingestion to death is typically under 90 minutes, with irreversible neurological injury occurring well before that point.
Sources are sparse due to the nature of the subject, but data from toxicology, emergency medicine, and rtd literature all roughly align on these figures.