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Confined spaces: risks and preventive measures

Confined spaces: risks and preventive measures

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Confined spaces are dangerous because they have narrow access means, both inside and outside, entailing a lack of natural ventilation and a stagnant atmosphere.


Most serious or even fatal accidents are caused by an oxygen-deficient atmosphere, the presence of toxic gases or vapours, an explosion or a fire.




What is a confined space?

Confined spaces: Some example
Confined spaces: Some example

They are many types of confined space – they can be located underground or in the air, but they are always small in size. They are defined as: an area that is partially or completely closed, and not suitable for people or designed to be occupied by people for long periods of time. Performing work inside tanks involves significant health and safety risks because tanks fall into the category of confined spaces.

The sectors most affected by this type of work are:

  •     Chemical industry: all types of tanks, cisterns, reactors, etc. that have contained toxic, corrosive, flammable or explosive substances
  •     Food industry: tanks, wineries or cellars in inert (nitrogen) conditions (presence of gases such as CO₂, SO₂)
  •     Transport sector: road and rail tankers, barges, vessels, planes, etc.
  •     Sanitation: tanks, sewers and collectors for cleaning, degassing and decontamination operations
  •     Farming: silos, wells, pits
  •     Welding: work in metal enclosures that have contained flammable materials or inside poorly ventilated areas

To find out more about confined spaces, please read our article: click here

Pour en savoir plus sur les espaces confinés, consultez notre article : Cliquez ici

Main hazards and risks of confined spaces

Main hazards and risks of confined spaces
Main hazards and risks of confined spaces

A hazard is the sum of all the factors that constitute a threat, a risk for people or their environment. In a confined space, there are a wide variety of hazard sources:

  •     Toxicity: solids such as sludge, liquids such as contaminated water, gases such as H₂S
  •     Ventilation: insufficient natural ventilation
  •     Access: restricted access

A risk results from the assessment of the probability that a hazard will occur. Risks related to the atmosphere are induced risks such as:

  •     Asphyxiation/Anoxia
  •     Poisoning
  •     Explosion / Fire

People performing work in confined spaces face other types of risks related to: the road (marking), falls (work at height), burns, drowning, presence of asbestos, burial, electrocution, biological, handling & postures, and so on.


Oxygen level in the air and consequences for humans

Usually caused by a lack of ventilation leading to the build-up of gas and toxic vapours, the formation of an explosive or oxygen-deficient atmosphere.

  •     Asphyxiation: inability to breathe or breathing difficulties caused by a lack of oxygen
  •     Poisoning: inhalation of a toxic gas that may cause death, such as carbon monoxide, carbon dioxide, hydrogen sulphide, chlorine substances, ammonia, sulphur dioxide, ozone, etc.

Hypoxia / Anoxia is caused by an oxygen level of less than 19% due to fermentation, combustion (welding, fire, etc.), metal oxidation (rust), a gas leak, etc.

  •     Hypoxia: reduced oxygen concentration in the blood
  •     Anoxia: organs and living tissues do not receive an adequate oxygen supply.

Explosion / Fire

The fire triangle
The fire triangle

In a confined space, any fire – even a minor one – can have dramatic consequences that far exceed those that would have occurred in the open air. Smoke can be poisonous and the fire can trap people inside, preventing them from getting out through the access doors.

Hydrocarbon compounds such as acetylene, ammonia, hydrogen, propane, propylene and methane are all flammable gases. They are also known as combustible gases. These gases pose a risk of explosion when they are present in poorly ventilated areas.

Combustion is a chemical reaction in which oxygen mixes quickly with another substance, resulting in the release of energy, in the form of heat or even flames. A fire is triggered when three factors are combined:  the presence of flammable gases (methane by fermentation, hydrocarbon vapours, etc.), inadequate ventilation and a trigger (spark, flame, the build-up of static electricity, etc.).

Preventive measures BEFORE carrying out work

  • Désigner un responsable compétent pour l’évaluation des risques propres à l’espace confiné.
  • Obtenir les autorisations administratives et arrêtés de voiries pour une interventions sur la voie publique.
  • Former les intervenants : l’employeur doit former ses équipes afin de pénétrer dans les espaces confinés
  • Délivrer un permis de pénétrer, pour cela l’employeur doit s’assurer :
  • S’assurer que les détecteurs de gaz soient étalonnés et entretenus suivant les préconisations des constructeurs
  • Avoir préparer un plan d’intervention des secours
  •     Appoint a qualified person to make an assessment of the risks inherent to the confined space.
  •     Obtain the administrative permits and road work orders required to carry out work on public roads.
  •     Train workers: employers need to train their staff in how to enter confined spaces.
  •     Issue a permit to enter a confined space. To do this, the employer needs to make sure that:
    •         there is a person present who is trained in how to take and interpret measurements using gas detectors;
    •         the provisions laid down in the risk assessment have been applied;
    •         the work performed in the confined space is under the surveillance of a qualified person who has the skills to intervene in the event of an incident, while remaining in a secure area outside of the confined space;
    •         the supervising staff member has adequate communication means.
  •     Make sure that the gas detectors are calibrated and serviced according to the manufacturer recommendations;
  •     Draw up an emergency rescue plan.

Preventive measures DURING work

An operator is appointed to survey the work from the outside, remain in contact with the people inside the confined space and ensure compliance with the instructions in the work permit with regard to:

Marking out of the work area

You need to protect the openings providing access to the space and mark out the work area to avoid any risk of falling for people who are external to the job, as well as the risk of traffic accidents.

Prevention: Protect the openings and mark out the work area


Good ventilation can offset many risks such as the build-up of gas (poisoning), anoxia and asphyxiation (lack of oxygen) as well as removing one of the 3 elements of the fire triangle. This is why you must carry out a test of the atmosphere before entering the confined space.

Prevention: it is essential to ventilate the area for 20 minutes and to test the atmosphere just afterwards. Be careful about where you put the fan and avoid power generators, sources of pollution and exhaust pipes.

Gas detector

A multi-gas detector (oxygen, carbon monoxide, H₂S, explosive gases such as methane and toluene) is used to test the atmosphere in the confined space. It is placed at the end of a cable or stick so that the atmosphere in the area can be measured from the outside.

In dangerous situations such as the release of disolved H₂S, a gas leak or faulty ventilation, the detector raises the alarm (visual and audible warning, vibration). If this occurs, you will need to ventilate the area again for a further 20 min.

Prevention: All workers must have a portable gas detector with them so that they can check the atmosphere at all times.

Work at height

There is a high risk of falling, especially if the work involves coming down a ladder. You also need to be careful about the condition of the ground, and handle any changes in level.

Prevention: you need to wear a harness hooked up to a tripod or davit arm and be fitted with a retractable type fall arrester connecting the harness to the outside (at the anchor point, as per NF EN 795).
Permit to work in confined spaces with all anchor points and anchor devices.

Self-rescuer (Category 3 PPE)

If the multi-gas detector raises the alarm a second time, this means that the atmosphere in the area is not breathable. You need to wear breathing apparatus (self-contained, air line breathing apparatus, etc.) if you need to work in a confined space. Self-rescuers provide respiratory protection by isolating the worker’s lungs from the surrounding atmosphere using compressed oxygen. They should never be used to perform work but only for emergency rescue operations.

Prevention: All workers entering a confined space need to have a self-rescuer and know how to use it.

How do we prepare to carry out work in a confined space?

Titre du push

The equipment

X-AM 2500 FLEX
Titre du push


Training in confined spaces
Formation en espaces confinés

In order to issue a permit to carry out work in a confined space, the employer needs to make sure that staff have received appropriate training and:

  •     Know the specific risks related to confined spaces, especially those concerning the atmosphere;
  •     Are able to perform the required tasks safely;
  •     Understand the purpose of safety equipment (gas detectors, self-rescuers, harnesses, etc.) and rescue equipment and know how to use it;
  •     Know the right behaviour to adopt in the event of an incident or accident.

Employers will keep an up-to-date folder recording the type of training courses completed, the trainer’s organisation and qualification, the dates on which the training courses took place.
A special procedure for certifying the required skills has been put together – it is known as CATEC (Authorisation to work in confined spaces, for the water treatment and waste water management sector).

FPS - Organisme de formation
FPS - Organisme de formation

La formation chez FPS c’est les spécialistes des Espaces confinés  

Partenaire de BE ATEX, Formation Prévention Sécurité est spécialisée dans la formation aux espaces confinés et CATEC, FPS utilise des nouvelles techniques pédagogiques basées sur l’approche par compétence. Nos formateurs réalisent votre ingénierie de formation complète basée sur le savoir, le savoir-faire et le savoir-faire dispose de l’ensemble des équipements et outils pédagogiques, des équipements de dernière génération (G7C, BW CLIP 4, Ari etc…). Les formations sont rendues les plus vivantes, conviviales et réalistes que possible par l’application des principes suivants : Discussions-débats sur les expériences vécues. Adaptation du programme et des mises en situation aux risques et activités spécifiques de la structure. Création d’un climat serein et dénué de jugements propice à l’apprentissage et à la participation active de tous. Utilisation de simulateur de formation en espace confiné à disposition.

Lieux d’intervention :

Formation Prévention Sécurité intervient sur votre site pour former vos personnels avec des contenus et des méthodes pédagogiques éprouvées, avec la possibilité de mettre à votre disposition du matériel, et simulateur de formation espace confiné. Nous avons des sites pédagogiques sécurisées à la location aussi. Nous intervenons sur l’ensemble du territoire français et dans le monde (Maroc, Guinée, Algérie, Gabon etc…).