Yes too much oxygen entering your body is indeed harmful to your health and could cause a person to die.
That's why it's important to make sure the oxygen levels on an oxygen tank or an oxygen machine are set correctly otherwise you risk serious issues with your health and potential death.
Too little oxygen and you can suffer brain damage as well as harm your heart and too much oxygen can cause your breathing to slow down which can result in death.
Our bodies need oxygen to survive but when you get too much pure oxygen you can begin to experience nausea, dizziness, muscle twitches, and convulsions.
So make sure you get trained to use the oxygen when you need to use oxygen.