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A Safety Guide to Working in Confined Spaces

Confined Spaces Prepare for maintenance work in confined spaces the best you can in order to ensure your employees’ safety.

Some maintenance work requires entering confined spaces, where confined space hazards can result in serious or even fatal accidents. In order to prevent work-related risks in confined spaces, one needs to make the area safe and use appropriate protective equipment, but also to prepare correctly by assessing the risks through professional confined space training and by following appropriate health and safety regulations and confined space regulations.

What is a confined space?

Definition of an enclosed space

A confined space is defined as a place combining the following characteristics:

  • A completely or partially closed space, which has not been designed to accommodate workers in the medium to long term.
  • A difficult to access space which needs to be temporarily occupied to complete maintenance work.
  • A space with a dangerous atmosphere, due to the presence of fluids, substances or chemical residues, a lack of ventilation or because of the nature of the work to be done.

An enclosed space is therefore dangerous and all maintenance work must be carefully planned to eliminate the different risks as much as possible.

Which places can be considered as confined spaces?

Confined spaces are found in many industries, including:


(silo, wells, pits)


(tanks, wine cellars, cold rooms)

Chemical Industry

(tanks, cisterns, reactors)


(pipes, sewers, main sewers)


(main sewers, storage facilities)

Transport Network



(crawl spaces, cellars)

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Is it dangerous to work in confined spaces?

Why are the risks higher in an enclosed space

Panneau atmosphère asphyxiante pour espaces confinés

The layout of a confined space can make it particularly dangerous for workers who have to enter the space. Confined spaces are often difficult to access, both to get in and to get out. They can be narrow or low and don't allow for optimum movement. In cases of immediate danger it may be difficult for the worker to escape quickly. It may also be difficult for a supervisor to assist a stuck or discomforted worker.

Apart from the lack of ventilation, which can prevent the renewal of oxygen, conditions can change very quickly because of the work done, or because of external circumstances (sudden rise in water or release of toxic substances). If the safety of the worker is threatened then he or she will need to evacuate the premises urgently and the above difficulties will need to be taken into consideration.

By definition, a confined space is a place with an atmosphere with little or no air renewal. Therefore, there is frequently an accumulation of toxic vapours or gas, to the detriment of oxygen levels. A “breathable atmosphere” contains 21% oxygen, the alert threshold being at 19%; below that, one needs to work with a respiratory protection apparatus. Below 17%, described as the danger threshold, the first symptoms of discomfort appear. A worker who is required to enter a confined space will therefore be exposed to the risk of not being able to breathe correctly without assistance, and being exposed to toxic substances. It is therefore vital to ensure that there are safe oxygen levels in a confined space.

When work procedures are written, special attention must be given to the emergency response procedure to allow for a worker’s evacuation.

Any confined space must be indicated by a “Confined Space” sign in order to prevent unauthorised persons from entering it by mistake.

Confined Space Signage

In general, any confined space work environment must be indicated with an appropriate safety sign in order to prevent unauthorised entry into this area by mistake.

What are the dangers related to confined spaces?

There are numerous risks related to work carried out in confined spaces:

  • Asphyxia and anoxia, if oxygen becomes scarce or is replaced during the maintenance work by toxic gases, which can cause headache, loss of consciousness, etc.
  • Poisoning following inhalation and ingestion of toxic substances released during the maintenance work or skin contact with such substances.
  • Electrocution, fire, explosion, in the event of the release of gas, excessive heat, an electrical fault, etc.
  • The risk of a fall if a safety harness isn’t worn or due to a faulty safety harness.
  • Collapse within the enclosed space and/or burial.
  • Drowning in the event of a sudden rise in water, especially when working on a water system.
  • Burns caused by leaking chemicals or hot water pipes.
  • Hearing risks: confined spaces can amplify sounds, which can damage the hearing.
  • Thermal hazards: temperatures can be extremely high or, conversely, extremely low.
  • “Unpredictable” risks, particularly risks of “complications of an accident” if the worker panics when a dangerous situation arises

Each maintenance task is different and the risks can differ according to the place’s technical characteristics, the nature of the work undertaken, substances potentially present in the atmosphere or the pipes, etc.

What steps should be taken when entering a confined space?

How can maintenance work in a confined space be made safe?

Before allowing a worker to enter a confined space, one needs to secure the space and ensure that the atmosphere poses no immediate risks. Therefore, many procedures should be followed:

  • Isolate the area: secure the surroundings with galvanised steel works barriers, indicate hazards with work signs and construction signs, ensure the correct assignment of machines and gates (from the outside as far as possible, or if this is not possible, from the entrance to the area).
  • Aerate and ventilate the enclosed space as much as possible to obtain a minimum air renewal. Ventilation must be maintained during the entire duration of the work taking place and as close as possible to the worker.
  • Check the atmosphere and its oxygen and gas content from the outside after 20 minutes of ventilation, and again once inside the enclosed space.
  • The worker must not be authorised to enter the area if his safety cannot be guaranteed.
  • Put in place, if necessary, a fall protection system, as well as appropriate means to light up the enclosed space.
  • Ensure that contact between the worker inside the enclosed space and his or her supervisor will be maintained for the entire duration of the operation. To this end, use of walkie-talkies is specifically recommended, especially if visual contact is broken.

What equipment is necessary for maintenance work in a confined space?

In order for the worker to be able to enter the confined space, she or he needs to be equipped with all the PPE (personal protective equipment) suitable for the work involved and for the conditions s/he is likely to experience:

  • Overalls, gloves, safety goggles and safety shoes: choose from our wide range of PPE products.
  • Work mask (refer to our page dedicated to the choice and maintenance of respiratory masks for more information).

The worker must also have specific equipment:

  • gas detector
  • fall protection kit and harness
  • equipment to raise an alert or warning
  • helmet
  • headlamp

Seton offers you many products for the successful completion of maintenance work in an enclosed space.

How to prepare for working in an enclosed space?

A person should not enter a confined space without preliminary work: risk analysis, writing of procedures, certifications, any necessary entry permits, etc.
Specific procedures have been developed in order to reduce the risks related to enclosed spaces as much as possible.

Signalisation de sécurité lors d'une intervention en espace clos

Assessing potential risks inside the enclosed space

First of all, one needs to ensure that it is absolutely necessary to enter the enclosed space and that it is completely impossible to carry out the maintenance works from outside via pipes, valves, faucets, cameras, etc.

If the maintenance work proves to be necessary, the employer must take necessary measures to ensure the workers’ safety and protect their physical and mental health.

These measures include actions to prevent occupational risks through precise risk assessment, which should detail:

  • the size and shape of the enclosed space, precisely described thanks to reconnaissance carried out on site.
  • substances that may be present according to the current use and any previous use of the space.

Based on this analysis, the employer will need to write a detailed procedure, in which all scenarios must be taken into account by considering all the potential risks and describing the work to be undertaken, the equipment to be provided and the procedures anticipated.

Finally, in order for the defined rules to be followed, they need to be communicated on signs, and any concerned persons must be informed of the risks and procedures that apply. A supervisor should be appointed; he will see that the appropriate procedures are followed during the maintenance work.

Training for Working in Confined Spaces

The Employer's Obligation.

The employer is also responsible for training the team who will enter the enclosed space “An employer may need to appoint a competent person to ensure employees are adequately trained under the Management of Health and Safety at Work Regulations 1999, regulation 7.

The employer must therefore ensure that only those trained in confined space work are involved in the work whether they are employees entering the confined space or supervisors.

Any worker or supervisor involved in working in an enclosed space must understand theoretical knowledge, ie what is the definition of an enclosed space, and what are the risks involved in working in an enclosed space. In addition, the worker/ team must be up to date on current regulations regarding working in enclosed spaces.

  • Practical skills: know how to assess the situation, identify the risks, prepare for work in an enclosed space, develop emergency procedures, etc.
  • Risk assessment: do not take risks, adjust one’s behaviour and responses according to the situation.
  • If an assessment identifies risks of injury from work in confined spaces then the Confined Spaces Regulations 1997 will apply.
  • Whenever possible, avoid entry to confined spaces by, for example, doing the work from outside.
  • If work in a confined space is unavoidable then follow safe practices.
  • Put emergency arrangements in place before the work commences.

These duties, and how to carry them out are described in the sections below.

Avoid entering confined spaces

Is the intended work actually necessary or is there a viable alternative option available? Could the work be done in another way in order to avoid working in a confined space? Perhaps the work could be done from outside the confined space – for example, blockages could be cleared using remote devices or by using silos. Cleaning and inspection jobs can often be done remotely, without the need to enter the enclosed space through use of special tools and equipment.

Safe Work Systems

If maintenance work in a confined space cannot be avoided then ensure that a safe working system is in place to protect workers from injury. Risk assessment needs to be completed and appropriate precautions implemented. All relevant persons need to be properly trained to ensure that they know exactly what to do and how to do it safely.


A supervisor should be appointed to check that safety precautions are being followed and they may need to be present while the maintenance work is being undertaken.

Testing the Air

The air in a confined space may need to be tested to check that it is suitable to breathe. A competent person would need to test the air quality with an appropriate and correctly calibrated gas detector. Continuous air monitoring may be necessary in some circumstances.

Ventilation of Confined Spaces

Mechanical ventilation may be necessary to ensure an adequate supply of fresh air. The number of openings to the confined space may need to be increased to improve ventilation where possible. In instances where diesel-fuelled machinery or portable gas cylinders are being used, additional ventilation may be essential. Warning: petrol-fuelled engines are dangerous because of carbon monoxide from their exhausts and should therefore never be used in confined spaces.

Provision of Special Tools

Special lighting and non-sparking tools are essential when working in an environment with a potentially explosive or flammable atmosphere. When working in certain confined spaces, such as inside a metal tank, precautions such as extra-low voltage equipment (typically less than 25 V) can be a good preventative measure against electric shock.

Breathing Apparatus

If the air inside a confined space is not fit to breathe, due to fumes, gases or lack of oxygen, then special breathing apparatus needs to be provided. Warning: Never try to ‘sweeten’ the air in a confined space with oxygen as this can greatly increase the risk of a fire or explosion.

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