Short answer: A human can begin to suffer brain damage within minutes of oxygen loss, and survival without medical intervention becomes unlikely after about 10–15 minutes. The exact timing varies with individual factors and the cause, but the general consensus is that permanent brain injury can occur after roughly 4–6 minutes of severe oxygen deprivation, and death or near- certain severe damage follows if oxygen is not restored within about 10–15 minutes. Details and context

• Immediate effects: When oxygen supply to the brain is interrupted, mental functions deteriorate quickly. Consciousness can be lost within seconds, and brain cells begin to suffer within minutes. As time passes, the risk of irreversible damage increases sharply. [citations not shown here, summarized from clinical guidance and expert sources]
• Typical timeframes cited in medical guidance:
  • 0–1 minute: Brief loss of consciousness is possible if perfusion is interrupted.
  • 1–3 minutes: Brain cells begin to experience stress; early dysfunction may occur.
  • 3–5 minutes: Increasing risk of brain injury; neuronal damage becomes more likely.
  • 5–10 minutes: Severe brain injury becomes more probable; outcomes worsen.
  • 10–15 minutes: Survival without serious, long-term damage is unlikely; likelihood of extensive brain injury and death increases substantially.
• Exceptions and caveats: Some individuals with specialized training (for example, free divers) or specific medical circumstances may momentarily endure longer periods without oxygen, but such cases are the exception rather than the rule and typically involve extraordinary prepared conditions or additional factors (e.g., decreased metabolic rate, external interventions). These do not contradict the general rule of thumb above. [contextual knowledge from medical and safety literature]

What factors influence outcomes

• Cause of oxygen deprivation (cardiac arrest, drowning, airway blockage, smoke inhalation, etc.)
• Temperature (hypothermia can slow brain metabolism and extend tolerable windows in some cases)
• Age and overall health
• Immediate availability and effectiveness of resuscitation and oxygenation
• Time to professional medical intervention and advanced life support

Safety note

• In any real-life scenario involving potential oxygen deprivation, immediately Call emergency services and begin CPR if trained, focusing on high-quality chest compressions and rescue breaths as advised by local guidelines.

If you’d like, specify the context (e.g., CPR guidance, high-altitude exposure, drowning, or medical conditions) and the timeframe you need (e.g., first 4 minutes, or after 10 minutes), and the answer can be tailored with more precise guidance.