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Published on 09/06/2022

Marine Gas Poisoning Symptoms

Awareness of key signs of gas poisoning is a vital extra line of defence should an undetected leak occur. Although sourcing robust gas detection solutions is essential (more below), occasionally, gas leaks can occur without prior warning, leading to potentially catastrophic results.

Each type of gas affects the body and brain differently – making awareness of the different types of gas poisoning essential to identify which gas a person may have been exposed to and arrange appropriate treatment and remedial action. 

The toxicity of gases on board sea-going vessels is multiplied due to the confined spaces crew members often operate in.

It is essential to avoid further illness or fatalities on board to notice when someone may be suffering from gas poisoning and which type of gas their symptoms correspond with. 


Methane is the primary component of natural gas, so it’s often present on board tankers, cargo ships, or vessels using natural gas as fuel. Methane is naturally odourless and completely invisible to the naked eye – but a scent is usually added to make it more easily identifiable should a leak occur.  

When present in high amounts, methane reduces the amount of oxygen in the air we breathe, causing our oxygen levels to become depleted, leading to initial symptoms such as:

*Slurred speech

*Mood changes 

*Nausea and vomiting

*Vision impairment 

*Memory loss

*Facial flushing


More severe cases can also produce the following symptoms:

*Changes to heart rate

*Difficulty breathing



Without timely intervention, methane exposure can lead to death. 

Methane is also highly flammable and explosive, even in small quantities – so once a leak is identified, fast action is required to avoid further consequences. 


Oxygen can often be found on vessels as cargo or as medical or diving equipment. 

Although oxygen is a key component of the air we breathe, breathing in too much can cause a condition known as Oxygen Toxicity. Symptoms to look out for include:


*Throat irritation

*Breathing difficulties

*Chest pain

*Muscle twitching in the face and hands


*Blurred vision

*Nausea and vomiting

*Confusion and disorientation


Severe cases of oxygen toxicity primarily affect the central nervous system and can lead to cell damage and death – so, as is the case with all types of gas poisoning; early medical intervention is key. 


Carbon monoxide poisoning is often dubbed the ‘silent killer’ – because, as with many other poisonous gases, it has no smell or taste, making it undetectable without specialist equipment. Sixty people in the UK die of carbon monoxide poisoning each year – a number dramatically reduced in recent years by the prevalence of carbon monoxide detectors. 

When inhaled, carbon monoxide enters the bloodstream and mixes with haemoglobin, red blood cells that carry oxygen around the body. When this occurs, the blood can no longer carry oxygen, causing tissues and cells to fail and die rapidly. 

The initial symptoms of carbon monoxide poisoning aren’t always obvious and gradually get worse, especially during low-level exposure – so a breach can quickly become life-threatening. They also mimic flu or food poisoning, which can delay diagnosis. The best way to determine whether a person is suffering from carbon monoxide poisoning as opposed to flu is to check their temperature – with gas exposure; there won’t be any change as is often seen with an infection. 

Primary symptoms of carbon monoxide poisoning include:


*Nausea and vomiting

*Tiredness and confusion

*Stomach pain


Over time symptoms can worsen depending on the level of exposure, including:

*Loss of balance

*Vision impairment

*Loss of consciousness 


*Elevated heart rate (over 100 beats per minute)

*Chest pain


In confined spaces, the effects of carbon monoxide are accelerated, and death can occur in a matter of minutes – so swift action is key. 


Like oxygen, exposure to small amounts of hydrogen is fine – but when a leak occurs and large amounts are inhaled, hydrogen poses a significant health risk. 

Like methane, hydrogen sulphide is often given a scent to warn of a leak – but this is not a failsafe protection method against hydrogen poisoning. 

Symptoms of hydrogen sulphide gas poisoning include:

*Nausea and vomiting


*Watering eyes and eye irritation

*Digestive upset and loss of appetite 




*Loss of smell

After some time, hydrogen exposure can cause loss of consciousness and collapse, eventually becoming fatal without intervention. 

How intelligent gas detection solutions can keep your crew safe

Having a reliable front-line defence against the dangers of gas leaks is key on board any vessel – large or small. As marine safety specialists, we’re proud to have developed world-leading gas detection solutions specifically equipped to deal with the unique challenges posed at sea. 

Our portable and fixed gas detectors boast an array of features, including easy maintenance, immunity to sensor poisoning and superior protection against dust, dirt and moisture to offer complete peace of mind to keep your crew safe from the dangers of gas. 

Discover gas detection solutions from Martek Marine today.