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lukantoday at 8:46 AM1 replyview on HN

No. "Poison" refers to a substance toxic to humans, but we can be exposed to pure oxygen and breath it very fine. But yes, oxygen is dangerous.


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Symmetrytoday at 10:54 AM

"Poison" can also refer to a substance toxic to other animals. We say that chocolate is poisonous to dogs for instance. And a good fraction of Earth's biosphere was killed off by oxygen poisoning in the first of Earth's great mass extinctions.

Also, the dose makes the poison and excess oxygen actually can poison humans. Deep sea divers have to worry about excess oxygen inducing seizures if they mess up their breathing gasses enough. And even 100% oxygen at regular pressure will slowly damage the lungs, something ICUs have to worry about.

Nick Lane had a great book about oxygen, Oxygen, which maybe isn't as good as his book about mitochondria but is well worth reading.