Hello @caregiver4
When I still worked in Respiratory Care, now and then we would have to re-instruct patients/family on the use of their O2 tanks upon leaving the emergency room. It usually included keeping the oxygen saturation at or above what the doctor ordered. Whoever your home care/O2 provider is should be able to also provide you with more information and answers to your specific questions. Very important .

You're more than likely using what are called 'E" cylinders which would only last 1 hour and 28 min @ 8LPM.
For transport I always recommended taking an extra tank or two to compensate for unexpected delays.

There is a conversion factor for every size O2 tank. For the E tank it's .28
You can always calculate how long your tank will last at any given LPM.
.28 x PSI (pressure in the tank) divided by LPM then divided by 60min equals the duration.
Ernie