Oxygen FAQ

Up to date, expert answers to frequently asked questions (FAQ) about oxygen supply systems, respiratory care and pulse oximetry written by OCC & collaborators.

Oxygen Quality & Safety

  • Most are not considered reusable per manufacturer specifications 
  • Check with the manufacturer specification and clinical guidelines to determine if reuse is safe
  • Steps for disinfection must be closely adhered to and may be manufacturer specific 
  • Some reusable devices (e.g. some ventilator circuits) may have a finite lifespan (e.g. a predefined number of sterilizing cycles)
  • Reusability of respiratory care devices is often debated and may vary based on local/national practice guidelines and regulations   

Click here to review WHO tips for cleaning and disinfection of respiratory equipment 

Additional resources:


PSA plants need to be operated and maintained safely just like any other industrial motor and machinery, but they are not inherently explosive or combustible. The electrical system must be installed properly and safely. However, oxygen is an accelerant for combustion (fire). So, if there is an open flame or ignition source, an enriched oxygen atmosphere can highly accelerate fire. If oxygen is being exhausted even around the plant, there should be no ignition sources, no open flame, no smoking, no sparks allowed. If high pressure oxygen cylinders are being filled, there are additional safety considerations. NOTE: Electricity requirements are pertaining to the model and specification of each individual PSA plant, this specification must be provided by the PSA manufacturer.

FAQ by Assist International

  • Without access to an oxygen analyser it can be difficult to determine the gas contents in a cylinder. International standards for color of cylinders are not straightforward.
  • Most cylinders are filled using pressure swing adsorption (PSA) oxygen plants and thus have a maximum FiO2 of 95%  and often considerably less.
  • Older oxygen cylinders may be black with a white top. Outside of these standards many variations also exist.  All the cylinders in the images below contained oxygen.
  • Oxygen analysers should be used to determine gases before use. Cylinders require routine testing and cleaning by certified technicians. Outlet fittings should be examined for damage or corrosion.

This depends on if the source is liquid or PSA. Plant manufacturers are required to provide and meet certified quality standards and the machine will indicate the purity level during production. If the device is new, you should request the quality certificates. Please download the WHO generic specifications for PSA plants (See our supplementary resources). For periodic checkups, you will need oxygen analyzers.

All devices, including medical devices, should have a quality assurance process that is related also to the documents that the manufacturer provides, or can provide you, from the manufacturing site. We have published the WHO technical specifications that help to have a generic idea of what the standards and certifications are that you need to have in the output of the oxygen generator plants. If the plants are already in style and working, and you want to monitor the oxygen purity…normally in the control panel you will be able to look at what the purity is that they are giving to you. From there you could troubleshoot accordingly. You may also ask the manufacturer or authorized distributor to provide you with specific oxygen analyzers that can help you do the required maintenance and change the filters.

  • Provided by Assist International

We always advise to have a small 1Kw uninterruptible power supply (UPS) feeding the control circuit and PLC.  It is inexpensive protection.

FAQ by Assist International

There could be many reasons for this. If it is connected to the pipe network, it is possible the design of the pipe was not done correctly. Under “Supplementary Resources”, there are recommendations posted about rational use of oxygen that can provide further detail.

FAQ by Assist International

Here are some tips on how to safely conserve oxygen depending on the local context:

  1. Be cautious with high flow nasal cannula – high flow nasal cannula uses up to 60-70 LPM flow and can deplete stores quickly. This delivery device generally should not be used on cylinders unless a manifold system is present and a large cylinder pool is present. Additionally, even when supply may be ample, multiple HFNC devices in simultaneous use may cause system pressure failure or a rate of decline that causes excess freezing of liquid oxygen sources (which will decrease liquid oxygen output further). Always wean patient flows as quickly as possible and transition to alternative lower flow devices as soon as tolerated. There are some turbine and Venturi based devices which do not require a robust medical air supply, but these devices still consume O2 at high rates. 
  2. Use evidence based SpO2 goals and avoid hyperoxia – Avoiding higher than necessary SpO2 goals will save vast quantities of oxygen (Read more on Optimal SpO2 Goals). The difference in SpO2 goal of 90 vs 92% in COVID19 patients can translate to 2-3x less oxygen utilized. This requires continuous or frequent pulse oximetry checks and careful, frequent titration. (see SpO2 goals). There are multiple auto-titration devices that are receiving increasing attention, but yet to see widespread use. 
  3. Consider oxygen conserving devices – There are multiple types of oxygen conserving devices, which may or may not be useful depending on the use case. These devices include oxymizers (both pendant style and nasal reservoir style) as well as conserving devices that are placed on the cylinder directly (also known as ‘pulse dose’ devices). Reservoir-based devices conserve oxygen by enabling a higher FiO2 with lower flow rate as the patient is breathing some oxygen from the reservoir. These devices were designed to work in patients with chronic lung conditions, and their performance in patients with acute respiratory failure is largely unproven (i.e. if a patient has a higher minute ventilation). Pulse dose devices can be expensive. There are numerous other oxygen delivery devices that claim or prove oxygen conservation, however, for most of these devices performance and outcome data are lacking for acute respiratory failure patients.  
  4. Consider liquid oxygen when possible –  this is the most efficient way to store and produce oxygen, based on size:capacity. However, liquid oxygen requires considerable infrastructure on site and regionally(e.g. roads, trucks, oxygen separating plants, etc). 
  5. Utilize additional O2 storage methods – these may be mobile liquid oxygen units, additional cylinders (Size H/J), or reservoir devices.  
  6. Inspect and eliminate O2 system leaks – leaks in oxygen infrastructure and delivery devices are common. Common causes to include: 
    • Using excess flow
    • Not turning off devices that not in use (e.g. anesthesia machines or flowmeters)
    • Incorrectly secured fitting from cylinders
    • Leaks in high or low pressure tubing due to lack of adequate maintenance
  7. Utilize oxygen concentrators – Consider utilizing oxygen concentrators to preserve cylinders and central supply when possible. There are multiple ways to split an oxygen concentrator to maximize the benefit of its output for multiple patients.  
  8. Carefully adjust intentional leak for CPAP/NIPPV – properly used NIPPV/CPAP will have a leak. Too much or too little can be problematic depending on the interface and patient. Proper titration requires close monitoring and regular adjustment
  9. Account for Bias Flow & consider devices without bias flow – Some ventilators utilize continuous flow during the expiratory cycle – ‘bias flow.’ In some cases, this adds considerably to oxygen consumption (see ventilator settings in step 3 of this calculator) above and beyond minute ventilation consumption. See manufacturer specifications and account for this in planning. 
  10. Consider systems that allow on-site filling of cylinder – PSA plants and deployable oxygen concentrator systems (DOCS) can be used to refill cylinders. Specifications vary widely depending on need. 
  11. Frequent inspection and countermeasures to avoid liquid oxygen failure: 
    • Daily inspection to look for excess icing with increased use and colder weather, liquid oxygen evaporators may freeze – dramatically reducing O2 output. Regular inspection and countermeasures are critical (e.g. de-icing or warming systems to prevent freezing
    • Inspect daily for potential leaks
    • Maintain daily line pressure log and fill level
  12. Frequent inspection and countermeasures to avoid portable oxygen concentrator failure:
    • Avoid running beyond max flow (this can cause humidity to build up in the zeolite and cause decreased efficiency and failure)
    • Inspect and clean air intake filter regularly (weekly)
    • Ensure functioning voltage stabilization unit if applicable
    • Even when not in use, be sure to periodically turn on the concentrator for 30 minutes weekly – this will flush the system and filters of humidity which can damage the device
    • Never run the unit without proper filters in place
    • Keep the air intake away from walls and curtains
  13. Frequent inspection and countermeasures to avoid cylinder failure:
    • Keep regulators and valves dust free
    • Avoid (fire) ignition sources
    • Ensure cylinders are stored and secured properly to prevent falling over
    • Always open cylinder valves slowly
  14. Estimate your burn rate and plan ahead – in some settings oxygen shortages can be avoided or ameliorated by planning ahead. Keeping track of daily facility consumption and modeling surge scenarios can help with planning for production and maintenance (PSA plans), cylinder numbers needed, refill frequency (liquid oxygen). There are many tools to help with planning. The online interactive tool (below) helps quickly model ward scenarios with varying levels of detail.  
  15. Ensure adequate power and backup power for PSA/concentrators – power failures can be a significant and abrupt cause of oxygen supply failure. If dependent on oxygen concentrators (whether portable or PSA plant), it is imperative to:
    • Utilize voltage stabilization units where power supply voltage is variable
    • Implement and regularly test backup power supply and/or backup cylinders in the event of power failure


Additional Resources:

Oxygen supply and demand calculator by OpenCriticalCare.org 

Blakeman TC, Branson RD. Oxygen supplies in disaster management. Respir Care. 2013 Jan;58(1):173-83.

Compilation of oxygen planning tools and presentations by OpenCriticalCare.org

Frank’s Hospital Workshop Tutorials – Oxygen Concentrators – by Frank Weithoner

Oxygen conservation infographic – Branson et al, CHEST, May 2021

Elimination of a machine mounted inspiratory filter – If a bacterial viral filter is used between the circuit Wye and the patient, then an additional inspiratory filter between the machine and the inspiratory limb may not be necessary to protect the patient (so long as the machine is kept clean and an airway mounted filter and/or expiratory limb filter is used). That is a big “if,” and the use of an inspiratory limb filter at the circuit takeoff is to eliminate this chance of error.  

A single inspiratory filter setup (at the wye) has been suggested as an option in settings of severe shortage. This setup may create potential for error and subsequent contamination of the machine. Additionally, the use of one instead of two filters in series significantly decreased viral filtration efficiency. The impact on risk of viral contamination is unknown. 

Expiratory limb filter extended use (i.e. not changing between patients) has been suggested by some as an option if severe shortage is faced and appropriate bacterial viral filter is used at the patient. APSF

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