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Travel Health & Safety Blog

Oxygen Resupply: Everything You Need to Know


If you’re a medical officer onboard a yacht, you will almost certainly have faced tricky questions when refilling your cylinder abroad.

There are several reasons why Oxygen refill can be difficult, a few of the key ones include:

  • There is no one standardised global solution
  • Oxygen is a hazardous material
    • Under high pressure it is an oxidiser
    • It is a fire hazard
    • In some countries it is a prescription medicine and so should be considered as such - over and under dosing can be hazardous for the patient

As Oxygen therapy has become more widely adopted over the years, gas cylinders and lately Oxygen concentrators have become the standard methods of delivery. For the reasons mentioned above, these cylinders need to be treated with respect: don’t leave them out in the sun, use the case the cylinder was supplied in etc.

All medical and non-medical gas cylinders are pressure vessels, rated for high or low pressure depending on the gas in them. All cylinders must be tested and date-stamped at regular intervals; these tests are mostly done every 5 years.

Tests can only be done by a certified agency because it is dangerous and illegal in most countries to refill a cylinder that is out of test and not certified for use in the country you’re filling in.


Although medical and non-medical gas cylinders are colour-coded to safety, the colour codes are not universal, Oxygen Cylinders commonly come in the following colours:

  • Some areas of Asia: Black body and white shoulder.
  • UK and EU: Often entirely white
  • US: Frequently all-green or have a green collar and a lacquered aluminium body
  • Certain specific industries and countries: May have other colours, including blue.
  • Oxygen can also be stored in scuba-cylinders which can be any colour (always be very careful and ensure proper labelling)

It’s important that you are certain what the content of the cylinder is, for example if you connect a nitrogen cylinder to a patient it'll kill them quickly and with CO2 gas (coloured grey) almost immediately.

You cannot just rely on colour alone, the cylinder will need to have a certified contents sticker, stating clearly ‘Medical Oxygen’ (in some cases ‘Aviation Oxygen’)

If there is any doubt as to the contents of the cylinder you can analyse the gas, using a Nitrox oxygen analyser.

Each gas has a specific valve and regulator combination that prevents the wrong gas being connected, this means that a nitrogen cylinder cannot be connected to a medical oxygen regulator – because the parts are not compatible.

In many countries there are a large number of other connection standards that may not be compatible with your system. The most common portable oxygen connection standard is the CGA 870, commonly known as PIN index. The washer that seals the regulator to the valve should be a Bodok Seal (rubber washer encased in a brass ring) it should never be a plastic (crush) washer due to the pressures that Oxygen is supplied in the EU.

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It is important to always carry a sufficient supply of Oxygen, plus a reserve for what your expected medical needs may be. If possible, we also recommend having an onboard Oxygen concentrator for an unlimited supply.

If you require Oxygen to be refilled it is often easiest to contact a technical dive shop as they will often have large supplies of Oxygen and be able to fill small and large quantities of cylinders - this will normally require a CGA 870 to DIN300 adaptor which most shops will have. If they do not have one they are easily sourced from technical dive websites.

If all other options are not available it may be necessary to locally purchase a system and/or compatible cylinder. Note: in some countries you can only rent cylinders and are unable to purchase.

If you are unsure of the system – reach out to our medical team who can advise.


A simple formula for calculating Oxygen duration is:

Volume of Cylinder in L (expressed on the neck as Litres, Volume or KG) * the pressure (Bar) / the flow rate

For example a 2L cylinder filled to 146 Bar with the regulator flow rate set at 15/L per minute will give you 19 minutes of Oxygen


In medical situations always contact MedLink first and if diving related, do not delay administering Oxygen.

If your vessel is travelling to more remote areas, we always suggest having an oxygen concentrator onboard with a crewmember that has appropriate understanding and training. Contact us to find out more.


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