Hydrocarbon releases: consideration of acute health effects

  • Safety notice: 4/2004
  • Issue date: Nov 2004


1. This notice reminds industry of the acute health effects associated with exposure to mixtures of hydrocarbons.

Action required

2. When assessing the risks from hydrocarbon releases, dutyholders should consider adverse health effects, as well as the potential for asphyxiation, fire and explosion. Emergency response procedures should therefore include consideration of the toxic effects of hydrocarbons.


3. Exposure to vapour/aerosol mixtures of hydrocarbons can cause acute adverse health effects at concentrations below those presenting an explosion or asphyxiation risk. The risk this poses during releases should be assessed and adequate controls applied.

Health effects

4. The acute health effects of hydrocarbon mixtures are generally associated with exposure concentrations at thousands of ppm. However, the exposure concentration and exposure duration leading to the onset of acute health effects varies between individual hydrocarbons, and this may influence the effects of exposure to mixtures.

5. Health effects associated with a single exposure to hydrocarbons are asphyxiation, narcosis (ie depression of the central nervous system; anaesthesia), cardiac arrest and aspiration. Of these, the first two are probably the most significant in the offshore context.

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6. Hydrocarbon gases/vapours can act as asphyxiants by displacing oxygen. Even if oxygen concentrations remain sufficiently high to support life, self-rescue may be impaired.


7. Effects depend on the substance(s), the concentration, and the period of exposure, but onset can be very rapid, eg if the concentration in the air is high enough, a few breaths can rapidly induce unconsciousness. Also, the difference between concentrations producing narcosis and those leading to death may be small.

8. Typically, narcosis is characterised by 'intoxication', leading through stupor to anaesthesia and, if not removed from exposure, to death by respiratory arrest. Some hydrocarbons may also produce convulsions. Features of intoxication (inappropriate behaviour, vertigo, nausea, giddiness) can impair self-rescue during an incident.

9. Narcotic effects are associated with all types of hydrocarbons that have sufficient vapour pressure, and the effects of individual components in a mixed exposure situation can be regarded as additive. Narcotic potency generally increases with molecular weight, so the risk is higher from mixtures such as condensate compared with mixtures of the lower gaseous hydrocarbons.

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Cardiac arrest

10. High concentrations of hydrocarbons, including those regarded as asphyxiants, can lead to cardiac arrhythmias and cardiac arrest, particularly where exposure is accompanied by stress and exercise.


11. Taking liquid aerosols of hydrocarbons directly into the lung can produce chemical pneumonitis, pulmonary oedema, haemorrhage and death.

Control of toxic risks

12. Offshore, hydrocarbons are subject to the Control of Substances Hazardous to Health Regulations 2002 (COSHH) and the Offshore Installations (Prevention of Fire and Explosion, and Emergency Response) Regulations 1995 (PFEER). In assessing and controlling the risks from hydrocarbons, and implementing emergency response procedures, dutyholders may deal with health and safety risks together, but the following paragraphs refer to the control of toxic risks.

13. Exposure to hydrocarbon gases/vapours may result from a breach of plant integrity. This breach may be intentional (eg for sampling, maintenance, pigging etc) or accidental (eg leaks or plant failure).

14. An intentional breach of integrity is by its nature readily foreseeable, and the risk is easily assessed. Controls applied for preventing exposure vary according to the risk, but include de-pressurising, de-gassing, closed systems for sampling, local exhaust ventilation and the use of respiratory protective equipment.

15. The basic control of accidental failure is prevention, eg by plant and systems maintenance. If integrity is breached, control will depend on a predefined safe system of work that needs to consider the likely locations and nature of significant releases, the ease of escape, area alarms and personal alarms, training and the use of respiratory protection (escape kit).]

Knowing where significant releases may occur and what hydrocarbons they are likely to consist of

16. Dutyholders need to have carried out sufficient analysis of their systems which contain hydrocarbons to know those areas where significant concentrations could be released in the event of foreseeable faults/leaks in the system, process control errors, or process upsets, and the likely nature of the hydrocarbons present.

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Ease of escape

17. In the context of acute health effects, confined or semi-confined spaces present the most difficult escape scenarios. Any place from which escape is potentially difficult, or where a gas/vapour release may not easily and quickly disperse (whether because of poor or failed ventilation), may also prove difficult to negotiate for someone affected by hydrocarbons.


18. The level at which area and personal alarms are set may be crucial to escape. The level needs to be set in relation to the nature of the stream, the local environment and the type of detector used. Alarm levels set for mainly methane gas streams may not be adequate for heavier streams such as condensate, especially in the type of situations noted in paragraph 17 above.


19. As well as the usual training for evacuation and emergency response (EER), employees should:

  • be aware of the toxic risks from hydrocarbons;
  • understand, use, and respond to area and personal alarms; and
  • where necessary, be trained in the use of escape kit.

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Respiratory protection

20. Equipment needs to be suitable and properly maintained. Because of the potentially rapid onset of narcotic effects, users need to be aware of the need to put on escape kit as soon as the alarms are triggered, and that supplying air to an affected individual may rapidly reverse the symptoms.

Relevant legal requirements

21. The relevant legal requirements are:

  • the Health and Safety at Work etc Act 1974;
  • the Management of Health and Safety at Work Regulations 1999 (SI 1999/3242), regulations 3, 4, and 7;
  • the Control of Substances Hazardous to Health Regulations 2002 (SI 2002/2677), regulations 6, 7, 8, 9, 12 and 13;
  • the Offshore Installations (Prevention of Fire and Explosion, and Emergency Response) Regulations 1995 (SI 1995/743), regulations 5, 8 and 9;
  • the Confined Spaces Regulations 1997 (SI 1997/1713) do not apply offshore but, along with the associated ACOP and guidance, they provide valuable advice where confined spaces present an additional risk.

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Further information

22. Any queries relating to this notice should be addressed to:

Health and Safety Executive
Hazardous Installations Directorate
Offshore Division
Lord Cullen House
Fraser Place
AB25 3UB
Tel: 01224 252500
Fax: 01224 252629

This guidance is issued by the Health and Safety Executive. Following the guidance is not compulsory and you are free to take other action. But if you do follow the guidance you will normally be doing enough to comply with the law. Health and safety inspectors seek to secure compliance with the law and may refer to this guidance as illustrating good practice

Updated 2024-02-09