Safer handling of oxygen

Welding oxygen is often considered harmless compared to acetylene or other combustible gases. However, this is not the case. Oxygen gives us life and forms around 21% of the content of the atmosphere along with nitrogen, argon, carbon dioxide (CO2) and a few other trace gases. This amount is sufficient to cause metal to rust, fires to burn out of control and certain foods to sour. Multiply that by 750 to 1,000 times and you can appreciate how dangerous the environment inside a high-pressure cylinder is.

Oxygen-Enriched Environments Are Fire Hazards

Any air mixture with an oxygen content of more than 21% is considered oxygen-enriched. A content of 23% oxygen in air, only 2% above the normal atmospheric content, represents an extreme fire and explosion hazard.

To start a fire, you need a source of ignition, fuel and an oxidizing agent. A source of ignition can be a spark from a grinder or welding process, a short-circuit in electric equipment or machinery overheating or misfiring.

The most common cause of oxygen enrichment onboard a ship is a leak in a system or component using compressed oxygen. Gas welding and cutting equipment is the most common of these. The risk of an incident occurring increases if the leak is in a confined space where a welder has stopped work for some time and then resumes, creating a spark.

Compared with a fire in normal air, a fire in an enriched oxygen atmosphere is more intense, burns at higher temperatures, higher speeds and has a greater heat output rate. In most circumstances, an oxygen fire cannot be extinguished until the source of oxygen feeding it has been isolated. The same applies in an oxygen-enriched atmosphere, but the amount of heat and fuel required decreases dramatically.

Important: Use approved trolleys or roll cylinders while holding them vertically upright. This ensures that the physically demanding task of lifting the cylinders is not required. When lifting cylinders, ensure that the right equipment is used.

The Hidden Dangers of Clothing

Not many seafarers are aware that clothing tends to absorb oxygen. The clothing of a person who has been exposed to an oxygen-enriched atmosphere retains a high concentration of oxygen for some time and is highly susceptible to fire. You must avoid sources of ignition and refrain from smoking for at least 15 minutes while the oxygen in clothing is replaced by normal air. Clothing must be loosened and aerated to help disperse any trapped oxygen.

Many so-called ‘non-flammable’ textiles burn fiercely in oxygen-enriched air. Garments treated with a flame retardant are useful only when the enriched-oxygen concentration is very low.

Important: Retardant properties reduce considerably when there is approximately 25% oxygen concentration or above, after which such clothing offers little protection at all.

Oxygen Deprivation Poses Asphyxiation Hazards

Lack of oxygen in the atmosphere is just as dangerous as enrichment. In this case, the risk is not of fire but asphyxiation. Asphyxiation is usually associated with nitrogen and other inert gases, such as argon, CO2 and helium, since they do not support life and can reduce oxygen concentration in the atmosphere to very low levels through displacement and dilution.

Being odourless, colourless and tasteless, inert gases give no warning of their presence and the inevitable reduction of oxygen. For an unaware crew member, the asphyxiation effect occurs without any preliminary physiological signs. This can be very rapid, taking as little as two breaths to cause unconsciousness and death.

Another cause of asphyxia can be decomposition of organic materials often resulting not only in lower oxygen levels but also increased levels of CO2 and sometimes even methane (CH4), carbon monoxide (CO) and hydrogen sulphide (H2S). The physiological effects of reduced oxygen concentration are summarised as follows:

Concentration of Oxygen Physiological Effects
21-18 % No symptoms detectable
18 -11% Reduction in physical and mental performance
11- 8 % Possibility of fainting within minutes without prior warning
8-6% Fainting occurs after a short time, with resuscitation possible if carried out immediately
6-0% Fainting is almost immediate, with brain damage likely even if rescued

Given longer exposure to an oxygen-depleted atmosphere, symptoms of asphyxia may present as rapid breathing and shortness of breath, rapid fatigue as well as nausea and vomiting. However, it is not unusual for a person suffering from asphyxia to be totally unaware of their symptoms, and they may even feel euphoric. Pay attention!

Most onboard accidents occur when crew members enter rooms or tanks that are connected to a nitrogen supply and have not been properly checked beforehand. Also keep in mind that a gas like CO2 is heavier than air and can accumulate at floor level. Complete entry is not necessary for a very serious or fatal accident to occur. The simple act of leaning in to inspect a tank with an oxygen-depleted atmosphere has resulted in death.

Tragically, there have also been many examples of seafarers going to the aid of victims and becoming victims themselves because they were not aware of what caused the initial incident.

Important: Any depletion of life-supporting oxygen below 21% must be treated as hazardous and all relevant precautions taken.

Air Quality Monitoring

Prevention is the surest solution to the above-mentioned scenarios. Air sampling and analysis is the only way to prevent crew members from entering an oxygen-enriched or depleted atmosphere. Equipping them with portable oxygen detectors means they can constantly monitor air quality even while performing their work.

Constant monitoring is vitally important, as some processes may either increase or reduce oxygen in the room or tank. When an oxygen reduction of oxygen occurs, be prepared also to measure for flammables and toxic gases like H2S and CO.

Important: Always remember to test gas detection equipment (bump testing) and/or verify calibration prior to using it to check atmospheres.

Wilhelmsen Ships Service always puts safety first

Our service does not stop at providing gas in cylinders. We also share our extensive knowledge of welding processes both on our website and through publications such as our Welding Handbook. We do our utmost to ensure customers benefit from our experience, and we have a reputation for setting high quality standards in the maritime industry.

WSS supplies oxygen in two sizes (5 and 40 litre) of refillable cylinders that can be picked up and returned in more than 2,000 ports around the world. Gases for calibration and bump testing of gas detection equipment are available in 10-litre refillable cylinders and smaller disposable cans.

Our global exchange program ensures availability and constant quality of safe cylinders. We have been doing this for more than 100 years, so you can trust us completely.

Check out our Product Catalogue ( for more details, and please do reach out to your local WSS representative.