Hello, I'm an expert in respiratory health and safety. When discussing oxygen levels, it's important to understand the context in which they are being measured. In a general indoor environment, a healthy oxygen level is typically around 20.9%. However, in certain high-altitude locations or specific industrial settings, the acceptable levels might vary.

For humans, hypoxia can occur when the oxygen level in the blood drops below approximately 95%. This is a critical threshold because it's when the body's tissues start to suffer from a lack of oxygen. At 85% oxygen saturation, most people will begin to experience symptoms of hypoxia, which can include shortness of breath, rapid heart rate, and confusion. Levels below 80% are considered dangerous and can lead to serious health issues, including organ failure and death.

It's important to note that these numbers are for arterial blood oxygen levels, which are different from ambient air oxygen levels. In ambient air, a drop below 19.5% can be considered a potentially dangerous situation, as it can lead to a decrease in cognitive function and other health problems.

In summary, for arterial blood oxygen levels:
- Below 95% can lead to hypoxia.
- Below 85% can cause noticeable symptoms.
- Below 80% is considered dangerous.

For ambient air:
- Below 19.5% can be considered a potentially dangerous situation.

Please remember that these are general guidelines and individual health conditions can affect a person's response to low oxygen levels.

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Normal arterial oxygen is approximately 75 to 100 millimeters of mercury (mm Hg). Values under 60 mm Hg usually indicate the need for supplemental oxygen. Normal pulse oximeter readings usually range from 95 to 100 percent. Values under 90 percent are considered low.read more >>