1. What are they?

Dangerous atmospheres are usually invisible and result from a change in the composition of all, or part of the air, particularly in a confined or poorly ventilated space. They may be caused by a leak of the goods or a chemical reaction between the goods and the environment, or as a result of a process. As a result the atmosphere may be toxic causing damage to the lungs or mucous membranes. In some cases it may lack sufficient oxygen leading to asphyxiation.

Fumesare given off by substances when processes are being carried out on them (e.g. when they are being heated). Some fumes are merely irritants, whereas others can be toxic.

Mists are particles of substances which are carried through the air in droplets (usually of water). They can settle on floors, making them slippery, and reduce visibility by settling on windows and light fittings.

Both fumes and mists can be dangerous when inhaled.

2. Where might they be encountered?

You can encounter dangerous atmospheres in many areas, the most common being:
Remember: fumes can remain in vats, tanks, drums, etc. long after the contents have been removed and additional care must be taken when entering confined or poorly ventilated spaces.

3. What about fumigants?

Fumigants are the dangerous substances you are most likely to meet. They are used to rid containers of rodents and insect pests. Fumigants are often used before the containers are shipped to the EU. If the containers are not properly ventilated on arrival, the fumes can pose serious hazards to officers working in them. There are three common types of fumigant, each posing its own particular hazards:

Methyl bromide (bromomethane): A highly toxic chemical which is widely used as a fumigant, particularly with containers of soil or timber. Although methyl bromide is highly toxic, the symptoms of poisoning can take several hours to develop. They include:
Even short-term exposure to methyl bromide fumes can cause discomfort, including headaches, sore eyes, stomach pains and numbness of the feet. These effects can last several days, but their severity depends on the concentration and on the length of exposure. Long-term exposure to methyl bromide can even result in death.

Aluminium phosphide (phosphine): Pellets of aluminium phosphide are used to fumigate containers of foodstuffs, tobacco and other perishable goods while they are in transit. The pellets deteriorate during the journey, releasing phosphine gas which destroys pests and then disperses within two or three weeks. Danger arises when:
Incorrectly fumigated containers are occasionally imported from Africa, South America and the Middle and Far East. Phosphine gas is colourless, but has an unpleasant odour reminiscent of decayed fish. If inhaled, it can inflame the respiratory passages and affect the central nervous system. Symptoms include tremors, nausea, vomiting, headaches and gastric pain. Serious cases can even lead to coma or death.

Hydrogen cyanide: This fumigant is less widely used than methyl bromide and aluminium phosphide, but is particularly dangerous. It has a smell reminiscent of almonds. Even at low concentrations it can cause dizziness, nausea, headaches and stomach pains, leading to unconsciousness and paralysis. Inhalation of high concentrations can rapidly lead to death.

For handling of fumigated containers see: Safe working in docks and freight areas - Examining freight and containers.

4. What damage can they cause?

Dangerous atmospheres, fumes and mists generally cause damage after they are inhaled into the respiratory system, attacking the lungs, brain, nervous system and other organs. However, they can pose other dangers by:

5. What can be done to reduce the risks?

If you work in confined spaces, such as on a vessel, hazardous fumes or gases could be present. You must use gas monitoring equipment to check both the level of atmospheric oxygen and if any hazardous fumes are present.

As many fumes, and some mists, are not visible, the most important thing is to know when and where they are likely to arise.

Often, notices will be displayed in danger areas on a trader’s premises. If proper ventilation is not provided but you have to work in these areas when mists or fumes are likely to be generated, you must wear respiratory protection.

If you work in confined spaces, such as on a vessel, hazardous fumes or gases could be present. You must use gas monitoring equipment to check both the level of atmospheric oxygen and if any hazardous fumes are present.

6. Flammable atmospheres

Flammable gases, vapours and mists are produced or used in many industrial processes. If they are not properly controlled, they can cause serious explosions or fires. Areas where such atmospheres are present are known as hazardous zones and are classified as:
The main requirement in these zones is to prevent any chance of the atmosphere being ignited, by excluding all potential ignition sources.

Some of these are obvious, such as matches, lighters and lighted cigarettes, but others are less so. Flammable atmospheres can also be ignited by:
Whenever any type of electrical equipment or hand tool has to be used in a hazardous zone, special precautions will be necessary. You must find out the trader’s safety rules and follow them.

You must use ‘intrinsically safe’ equipment whenever there is a risk that the atmosphere could be flammable.

See Safety torches and Intrinsically safe equipment.

You must refer to the legislation and the guidance of your national administration for more information.
The guidance contained in this section intended to serve as a general reminder of the risks that are sometimes encountered during the examination and sampling procedure and of the safety equipment that you should use and precautions that you should take.

Version Date Changes
1.0 12.10.2012 First version
1.1 01.11.2019 Update - small text modification
1.2 15.07.2021 Update - total text modification