News

HSE safety notice: high concentrations of hydrogen sulfide (H2S) in cargo and slop tanks

11:11, 23/5/2023

The Health and Safety Executive (HSE) has identified high concentrations of hydrogen sulfide in cargo and slop tanks onboard some FPSOs (Floating Production Storage and Offloading) and FSUs (Floating Storage Units) operating in UKCS.

The concentration levels are up to 16,000ppm and this is above the measuring limits of the standard portable gas monitoring equipment generally used onboard tankers and FPSOs, and may be undetected.

Sulphate that reduces bacteria present in cargo and slop tanks can generate hydrogen sulfide. Hydrogen sulfide concentrations over 1,000ppm are severely dangerous. as it can cause immediate collapse with loss of breathing, even after inhalation of a single breath. This gas sits still and corrodes, which can damage the hull structure and the cargo containment system.

It has been found that standard equipment may not be able to detect the high concentrations of H2S, which leaves a high number of workers at risk of exposure to the hazardous gas.

Workers are at risk of being exposed to H2S during operational activities involving breaking of containment, unintentional releases due to poor integrity of pipework attached to cargo tanks, or during regular venting operations to maintain cargo tank pressure within operational limits.

Duty holders must ensure that the installation has implemented a suitable hydrogen management process that complies with HSE offshore information sheet no. 6/2009, ‘managing hydrogen sulfide detection offshore’, if hydrogen sulfide is detected.

It has been urged that training should be provided to anybody onboard about the risks and any additional control measures that have been implemented. Also, all the gas monitoring arrangements for cargo and slop tanks should be fixed. This would help prevent exposure to toxic gas while monitoring portable gas monitoring equipment.

What is hydrogen sulfide and why is it dangerous?

Hydrogen sulfide is a colorless, flammable, highly toxic gas. This gas is also known as ‘dihydrogen sulfide’, ‘sewer gas’ and sulphurated hydrogen. High levels of exposure to the gas could be very dangerous and even lethal. This is dangerous for the body, as it inhibits the respiration of cellular respiration which damages the central nervous system.

Hydrogen sulfide is formed during the rotting of many organic materials. This is because H2S is heavier than air and it tends to accumulate at the bottom of poorly ventilated spaces such as sewers, ship’s cargo holds, overflow wells and storage tanks etc.

How does hydrogen sulfide poisoning occur?

Mainly, H2S enters the body through the respiratory tract, but it can also be absorbed through intact skin.

H2S poisoning is possible when you are in an area where the maximum permissible gas concentration is exceeded (in the air of the working area – 10 mg / m ³).

Hydrogen sulfide poisoning is usually acute and occurs when:

• Violation of safety at work.
• Violation of technological processes.
• Emergency emergencies.

Often, workers in industries where hydrogen sulfide is used or released are exposed to regular exposure to small doses of gas, which can lead to chronic occupational hydrogen sulfide intoxication.

Symptoms

The symptoms of H2S intoxication vary depending on how severe the poisoning is. With mild intoxication, the symptoms are:

• Profuse discharge from the nose, lacrimation, conjunctival hyperemia
• A feeling of sand in eyes
• Burning and soreness in the nasopharynx
• Hoarseness

With moderate poisoning, the symptoms are:

• Headaches
• Dizziness
• Nausea
• Vomiting
• Diarrhoea
• Severe weakness
• Motor discoordination
• Increased heart rate
• Hypotension

With severe poisoning, the symptoms are:

• Impaired activity of the cardiovascular system (tachycardia, arrhythmia, severe hypotension, threadlike pulse).
• Impaired activity of respiratory systems (superficial unproductive breathing, shortness of breath).
• State of euphoria.
• Often the victim is tuned or inaccessible to contact.
• Coma may even develop.
• Psychomotor agitation.

What to do if you or a colleague has come into contact with hydrogen sulfide

1. Take the sufferer out of the place of contamination.
2. Provide the sufferer with fresh air (opening windows/doors etc.)
3. If the sufferer is unconscious, lay them on their side or back with their head turned to one side to prevent possible aspiration to vomit.
4. Rinse nose, eyes and open skin with 2% soda solution (1 tsp of soda in a 200ml glass of water) or plenty of running water, rinse your mouth.
5. Apply cool eye lotions with 3% boric acid.
6. Apply 1-2 drops of petroleum jelly to the eyes.

How to prevent hydrogen sulfide poisoning

• To help prevent H2S poisoning, it would be necessary to comply with the safety requirements at the workplace.
• Employers should provide the workers with relevant training to ensure that they are aware of the dangers of H2S and how to protect themselves from hazardous gas.
• To help prevent poisoning from the gas, workers should be wearing personal protective equipment such as goggles and face masks etc. People at risk of exposure to the gas should regularly undergo preventive medical examinations.

If there is any suspicion that intoxication is caused by hydrogen sulfide, it is necessary to seek medical help. Treatment is symptomatic: in case of a collaptoid state, anti-shock therapy is performed, in case of convulsive syndrome, sedatives are administered, etc.

The antidote to hydrogen sulfide is methemoglobin, therefore, in case of severe poisoning, the introduction of chromosmon or 1% solution of methylene blue in glucose (10 ml of blue per 20 ml of glucose) is indicated – as a result, methemoglobin is formed, which binds H2S.

Can hydrogen sulfide poisoning be treated?

There is no proven antidote for H2S poisoning, but the effects of H2S can be treated, and some exposed persons get well. Persons who have had serious exposures may need to be hospitalized.

If you or anyone you know has been suffering from H2S poisoning and is experiencing the symptoms listed above, then you might be able to claim compensation. We urge you to discuss your complaints and symptoms with a medical professional and subsequently seek legal advice.

If you feel your injuries have been caused as a result of your work and wish to enquire about a potential claim for compensation, please contact us.

Resources:

High concentration of hydrogen sulfide (H2S) in cargo and slop tanks – Safety bulletin – HSE

Managing hydrogen sulfide detection offshore – hse.gov.uk

What are the dangers of Hydrogen Sulfide (H2S)? – SEMA Gases

Hydrogen Sulfide Poisoning – Symptoms, First Aid, Treatment, Consequences: Diseases 2023 – abchealthonline.com

Further reading

Respiratory disease claims – Oakwood Solicitors

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