Calculations: How Long Will An Oxygen Tank Last?

Your question. 

My dad wears 3 LPM oxygen at home oxygen. When he goes out of the house he has these little tanks. I think they are ML6 tanks. He is always stressed that they won't last very long. Tomorrow we have to go from the hospital to our house, which is about a 30 minute drive. He insists that I bring two tanks for the journey, but I'm wondering if we need that many. So, I am wondering how you determine how long tank will last on 3 LPM. 

My humble answer.

I completely understand your concern, and it's great that you want to ensure your dad has a comfortable journey. To estimate how long an ML6 tank will last at a flow rate of 3 liters per minute, you can use a simple formula:

Duration (minutes)=Flow Rate (in liters per minute)Tank Capacity (in liters)​×60

For an ML6 tank with a capacity of around 170 liters:

$\text{Duration (minutes)}=\frac{170}{3}\times 60$

$\text{Duration (minutes)}\approx 56.67\times 60$

$\text{Duration (minutes)}\approx 3,400.2$

Calculating this further, we can use another formula to convert this to minutes. 

        Duration (hours)=60Duration (minutes)​

For example:

$\text{Duration (hours)}=\frac{3,400.2}{60}$

$\text{Duration (hours)}\approx 56.67$

So, 3,400.2 minutes is approximately 56.67 hours.

So, at a flow rate of 3 liters per minute, one ML6 tank is estimated to last approximately 3,400.2 minutes or 56.67 hours. For a 30-minute drive, one tank should be more than sufficient. 

However, it's always a good idea to bring a spare for unexpected delays or emergencies, providing peace of mind during the journey. So, in my humble opinion, you are your father are both correct. You are correct in that one tank should be efficient to make the journey. But, your father is right in that it is always a good idea to have a spare tank just in case something unexpected happens.