100% oxygen under high pressure is dangerous

There is a fire risk, but competent chamber operators will make sure that patients don't bring in any ignition sources or highly flammable objects.

There will also be some pulmonary oxygen toxicity effects. Based on the protocol described those will be limited and resolve quickly in most patients.

The oxygen exposure is too limited to cause any significant risk of neurological effects, like a seizure.

So I don't know whether this treatment is actually effective but it's not particularly dangerous.

> make sure that patients don't bring in any ignition sources or highly flammable objects.

Out of curiosity, what would this include? Smartphones? Bluetooth headphones (to be used with smartphones that are outside)? Smartwatches?

Consumer electronic devices are usually not allowed. Every chamber has their own list of prohibited items. This one is pretty typical.

https://www.advocatehealth.com/assets/documents/subsites/lut...

My guess is that the mask is the only source of pure oxygen and that the rest of the atmosphere in the chamber has less oxygen than atmospheric air, making it still breathable because of the higher pressure.