Portable Oxygen: A User's Perspective

Compressed, Liquid, or Concentrator?

Portable Oxygen: A User's Perspective

Portable Use:
Compressed, Liquid, or Concentrator?

This is a continuation of the feature article, Home Use: Compressed, Liquid, or Concentrator?   This article focuses on sources of oxygen for portable systems..


I have reported on the two portable concentrators, AirSep's LifeStyle (image) in and Inogen's Inogen One (image) in Concentrators: Portable & Transportable. A portable concentrator may not be a first choice for most of us because of several factors, including cost. The focus here therefore will be on compress and liquid oxygen for portable use.

Some of the concerns I hear about portables are about system weight and how long the oxygen lasts. Manufacturers focus their advertising on these two features. Table 2 shows the relative benefits of compressed and liquid oxygen systems, based on average weight and average duration of the portable systems I have reported in the Compressed Oxygen and Liquid Oxygen sections of this website.

Table 2
Comparison of Average Weight and Duration

Compressed Oxygen Liquid Oxygen

B (or M6)
C (or M9)
Avg. Weight (lbs.)*
Avg. Durations @ Setting 2 (hrs.):
   Cont. Flow
    Pulse Flow**
Ratio: Pulse/Weight
*Includes conserver, case, spare batteries and a wrench, as required.
**Assumes a breathing rate of 20 bpm.

As the above table shows, not only does the typical liquid portable weigh less than both compressed oxygen configurations, it is also more efficient. The ratio of pulse flow to weight is highest for liquid portables. The ratio1.6 indicates that at setting 2 and breathing at 20 bpi, a user gets 1.6 hours of pulse oxygen for every pound he/she must carry. For the B  (or M6) cylinder, this ratio is 1.0, meaning the user gets one hour of oxygen for each pound, or about 60 percent less.

Listen to how Chip from NH, a founding member of  COPD-International , handles portables.
For me, there is a definite advantage to liquid oxygen. My lifestyle and work take me away for many hours at a time. Using the Helios (image) gives me "portablility." I use an oxygen unit the size of a canteen that weighs less than 4 pounds, which hangs from my waist. The Helios lasts me more than 8 hours, depending on my setting and breathing rate. I also carry the Stroller (image) as a back up, which gives me up to 6 Lpm continuous flow when I need it for exertion. This combination of tanks gives me up to 15 hour away from my 50' tether and the reservoir.
But liquid oxygen has a characteristic that bottled oxygen does not. Like dry ice, it evaporates. Left overnight, a liquid portable can lose a half liter of oxygen. On the other hand, a cylinder of compressed oxygen may be used day after day, until it is empty. Liquid oxygen users are dependent on having at home or in their vehicles liquid oxygen reservoirs from which they can periodically refill their portable tanks.
Since bottled oxygen does not evaporate, its users have the freedom to travel far from home for extended periods of time by transporting their bottles. Liquid oxygen users cannot remain away from their reservoir for more than a day. Extended travel for them means carrying a reservoir, which can be refilled periodically during a trip. Fortunately, there are liquid oxygen reservoirs that are small enough to fit inside a midsize car, an RV and van type vehicles.

So, the choice between compressed and liquid is really only a matter of convenience to you. In that regard, I present the following information about portable compressed oxygen (COX) and liquid oxygen (LOX) systems. This information is from manufacturers, reactions I have heard from users, and my own personal experience (I have been on oxygen 24/7 for four years, half that time on each system.) 

On Safety
COX- Compressed at 2,000 to 3,000 psi, can turn into a missile if severe damage occurs to its valve. Store cylinders securely in an upright position.
LOX- Stored at 20 psi, its primary danger is causing burns when the fill valves are touched after filling. Also, liquid oxygen continuously vents, so it should always be in a well ventilated area.
BOTH- require safe handling and have the same dangers regarding fire. For more information on safety, see Safety .
On Evaporation
COX- Compressed oxygen does not evaporate. If the contents gauge shows a cylinder to be half full and you close the cylinder valve, then the gauge will still show it is half full a day or two later. 
LOX- Liquid oxygen evaporates--in small portables at a rate of between 1 and 1.5 lbs. per day. Since these portables contain only 0.8 to 1.6 lbs. of liquid oxygen when full, you can expect your portable to be depleted in 24 hours, whether you use it or not. Oxygen in a reservoir will deplete at a rate of about 3 lbs. per day.
On Replacing or Refilling 
COX- Replacing an empty cylinder with a full one  requires agility with the hands and arms. For this reason the user should be connected to another source of oxygen while performing this task. 
LOX- The user can remain connected to and receive oxygen from the portable while it is filling.
On Surprises
COX- After replacing an empty cylinder, the user discovers the replacement has a defective valve and is empty. Be prepared with another replacement.
LOX- After filling a portable, the user discovers the portable has frozen and does not produce oxygen. Learn to fill so the portable does not freeze up. If not, be as prepared as the COX user.
On Replacement or Fill Procedures
COX- To replace an empty cylinder, close its valve with a wrench, unscrew and remove the conserver from the neck of the cylinder, and move the depleted cylinder out of the way. Move a full cylinder in its place, place the conserver over the neck of the cylinder then screw it in place, and open the cylinder valve. 
LOX- To fill a liquid portable, place the portable on the reservoir, press down on the portable, and lift its valve. When full, close the valve and remove the portable.
On Operating Positions
COX- Portable systems with electronic conservers will operate in any position. Some pneumatic conservers operate most effectively when the cylinder is vertical. For more information, see Pneumatic Conservers .
LOX- Most liquid systems will operate in a limited number of positions--on its back to vertical, but not on its side or upside down.
On Appearance
COX- Most units are contained in bags and do not draw attention. 
LOX- At high flow rates and under humid conditions, a unit will produce noticeable "smoke," snow, and condensation.
On Conservation
COX- Most users systematically start the day by using their partially filled cylinders because they do not want to appear wasteful by returning partially filled cylinders for refill. Such dedication impacts how these users organize the backups they carry with them. 
LOX- Users recognize that liquid oxygen will dissipate from both their portable and reservoir whether they are used or not. Knowing this, they will never partially fill their portables. They will begin the day by filling their portable and refilling them as needed.
The argument about which is best--compressed or liquid-- has gone on for decades. The important thing to know is that both can support you equally well when you are properly fitted to a system at a prescribed flow rate. If you have any questions about how well oxygen supports you, you should speak with your physician or oxygen provider. 

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© 2003 Copyright 
Peter M. Wilson, Ph.D. 
Founder of PortableOxygen.org

