The brain can survive without oxygen for only a very short time before damage begins. Brain cells start dying within about one minute of oxygen deprivation. At around three minutes, neurons suffer more extensive damage, and lasting brain damage becomes more likely. By five minutes, death becomes imminent, and at ten minutes, coma and severe, lasting brain damage are almost inevitable. Survival beyond 15 minutes without oxygen is nearly impossible

. More specifically:

• Loss of consciousness can occur between 30 seconds to 3 minutes without oxygen.
• Brain cells begin dying at 1 minute.
• Extensive neuronal damage occurs by 3 minutes.
• Death risk becomes very high by 5 minutes.
• Coma and irreversible brain damage are likely by 10 minutes.
• Survival beyond 15 minutes without oxygen is extremely rare

However, some recent research suggests that under certain conditions, brain activity may persist longer during resuscitation efforts, but permanent damage still typically occurs within minutes without oxygen

. In summary, the brain can only tolerate about 3 to 5 minutes without oxygen before irreversible damage occurs, and death risk rises rapidly after that timeframe