Guidance · Reviewed September 2026
What counts as a confined space in law, the hazards that kill people in them, what the Confined Spaces Regulations 1997 require of employers and the self-employed, and how to plan the work, the permit and the rescue before anyone goes in.
The short answer
The confined space regulations for Great Britain are the Confined Spaces Regulations 1997. Under them, a confined space is any substantially enclosed place where there is a reasonably foreseeable risk of fire or explosion, loss of consciousness, asphyxiation or drowning. It does not have to be small. The law sets three duties, in this order: avoid entry if the work can reasonably be done from outside; if entry cannot be avoided, follow a safe system of work; and have emergency rescue arrangements in place before work starts. HSE’s Approved Code of Practice L101 explains how to meet them. HSE says a number of people are killed or seriously injured in confined spaces in the UK every year, including people who try to rescue others without proper training and equipment.
| Key fact | Detail |
|---|---|
| The regulations | Confined Spaces Regulations 1997 (SI 1997/1713), in force since 28 January 1998 |
| Who has duties | Every employer and every self-employed person, including for work by contractors that is within their control |
| The three duties | Avoid entry (regulation 4(1)); safe system of work (regulation 4(2)); emergency arrangements before entry (regulation 5) |
| Official guidance | HSE Approved Code of Practice L101, Safe work in confined spaces, third edition, December 2014, and HSE leaflet INDG258 |
| Legal test | A substantially enclosed space plus at least one of five specified risks |
| Where they do not apply | Below ground in a mine, diving projects, and the normal work of a sea-going ship’s crew |
| Normal oxygen in air | 20.9%. L101 says below 16% can lead to unconsciousness and death |
| Rescue | Your own arrangements must be in place before entry. Relying on the emergency services alone does not comply |
On this page: Definition · Hazards · The regulations · Risk assessment · Safe system of work · Permit to work · Emergency rescue · Training · FAQs
What Is a Confined Space? The Legal Definition
The regulations define a confined space as “any place, including any chamber, tank, vat, silo, pit, trench, pipe, sewer, flue, well or other similar space in which, by virtue of its enclosed nature, there arises a reasonably foreseeable specified risk”. HSE’s Approved Code of Practice, Safe work in confined spaces (L101, third edition 2014), breaks that into two tests. Both must be met:
1. The space is substantially enclosed
It does not have to be enclosed on every side. Vats, silos and ships’ holds can have open tops or sides and still count.
2. A specified risk is present or reasonably foreseeable
One or more of the five specified risks listed in the hazards section below must exist in the space, or be introduced by the work done in it.
HSE’s leaflet INDG258 puts it more simply: a confined space is any space of an enclosed nature where there is a risk of death or serious injury from hazardous substances or dangerous conditions, such as a lack of oxygen.
Confined Space Examples
As well as the places named in the definition, L101 lists ducts, culverts, tunnels, boreholes, manholes, shafts, excavations and trenches, inspection pits, cofferdams, freight containers, ballast tanks, ships’ engine rooms and cargo holds, building voids, plant rooms, asbestos removal enclosures, unventilated rooms and the interiors of machines, plant and vehicles. Confined spaces are found in construction, water and utilities, telecoms, manufacturing, food and drink, agriculture, shipping and facilities management. Some dangers, such as vented gases, can also affect contractors and members of the public nearby.
Common Misunderstandings
- A confined space is not necessarily small. Grain silos and ships’ holds can be very large.
- It is not necessarily hard to get in or out of. Some have several entrances or large openings.
- It may be somewhere people work every day, such as a vehicle spray booth.
- An ordinary room can become a confined space for a while. Welding that uses up oxygen, paint spraying or cleaning with chemicals can create a specified risk. The space stays a confined space until the fumes have been ventilated away and the atmosphere has been tested as safe.
- Some are created on purpose, such as low-oxygen (hypoxic) rooms used to prevent fires in archives and server rooms, or stores protected by gas fire suppression systems.
- A cramped space with no specified risk is not a confined space under the regulations. Lofts, ceiling voids and some cellars still need a risk assessment, for example for manual handling and for getting an injured person out, but under other regulations.
Where the regulations do not apply
The Confined Spaces Regulations 1997 apply to all work covered by the Health and Safety at Work etc. Act 1974, with three exceptions: below ground in a mine, diving projects covered by the Diving at Work Regulations 1997, and the normal shipboard work of the master and crew of a sea-going ship. Each of those has its own legislation. Shore-based workers on board a ship are covered.
What Are the Hazards of Working in Confined Spaces?
The confined space hazards that the regulations address are the five “specified risks”. They arise from the combination of an enclosed place and a substance or condition that is already there, or that the work brings in, such as fumes from chemical cleaners or welding.
| Specified risk | How it arises |
|---|---|
| Serious injury from fire or explosion | Flammable vapour left in a tank, flammable dust such as flour, oxygen leaking from welding equipment, or leaks from adjoining plant that has not been isolated. |
| Loss of consciousness from a rise in body temperature | Hot work, boilers or furnaces that have not cooled, spaces heated by the sun, and strenuous work in protective clothing. |
| Loss of consciousness or asphyxiation from gas, fume, vapour or lack of oxygen | Sludge and residues disturbed by cleaning, sewer and slurry gases, exhaust from engines and generators, welding fume, inert gas purging, rusting inside closed steel vessels, and wood pellet stores. |
| Drowning from an increase in the level of liquid | Water surging through sewers after heavy rain upstream, or liquid entering from plant that has not been isolated. Drowning can happen in a small depth of liquid. |
| Asphyxiation or entrapment by a free-flowing solid | Grain, sugar, flour, sand, coal dust and similar materials that can engulf a person, typically in silos and hoppers. |
Other hazards, such as electricity, noise, collapse of the structure and moving machinery, are not unique to confined spaces and are covered by other regulations. L101 points out that where they are present in a confined space, the precautions will almost always need to be more extensive because of the enclosed nature of the space.
What Do the Confined Spaces Regulations 1997 Require?
Employers have duties under the Health and Safety at Work Act 1974 to ensure the safety of their employees and of others who may be affected by the work, which can include contractors and members of the public. Employees also have a duty to work safely and to take care of colleagues and others affected by what they do. On top of the Act, the Confined Spaces Regulations 1997, which came into force on 28 January 1998, place duties on every employer and every self-employed person. Those duties extend, so far as is reasonably practicable, to work by other people that is within their control, such as contractors.
Regulation 4(1): avoid entry
Nobody may enter a confined space to carry out work unless it is not reasonably practicable to do the work without going in.
Regulation 4(2): safe system of work
Where entry cannot be avoided, the work must follow a system of work that makes it safe and without risks to health. That includes suitable equipment in good working order.
Regulation 5: emergency arrangements
Suitable and sufficient rescue arrangements must be prepared before anyone enters, whether or not the emergency arises from a specified risk.
| Law | What it means for confined spaces |
|---|---|
| Health and Safety at Work etc. Act 1974 | The general duty to provide safe systems of work, information, instruction, training and supervision (section 2), and the duty on designers, manufacturers and suppliers of plant to design out the need for entry where they can (section 6). |
| Confined Spaces Regulations 1997 | The three duties above. L101 is the Approved Code of Practice. If you are prosecuted and have not followed it, you must show that you complied with the law in another way. |
| Management of Health and Safety at Work Regulations 1999 | Regulation 3 requires a suitable and sufficient risk assessment, recorded where there are five or more employees. This is where a space is identified as a confined space. |
| COSHH Regulations 2002 | Control of toxic gas, fume, vapour and dust. Respiratory protective equipment must be thoroughly examined at suitable intervals. |
| Lifting Operations and Lifting Equipment Regulations 1998 | Rescue lines, harnesses and lifting equipment used to lift people must be thoroughly examined by a competent person every six months. |
| PUWER 1998 and the Electricity at Work Regulations 1989 | Work equipment must be suitable for the conditions, including protected equipment where a flammable atmosphere is possible. See our PUWER guidance. |
| Construction (Design and Management) Regulations 2015 | Designers must eliminate or reduce foreseeable risks through design, including the need for anyone to enter a confined space to build, clean or maintain a structure. L101 predates the 2015 regulations and refers to CDM 2007, which they replaced. |
How to Carry Out a Confined Space Risk Assessment
Risk assessment is the key to making sure that work in confined spaces is carried out safely and that the risk of injury or death is reduced. L101 says the assessment must be carried out by a competent person: someone with the skills, knowledge and experience of the processes, plant and equipment involved to understand the risks and devise the precautions. Where a number of spaces, such as manholes on one sewer network, are broadly the same, a generic assessment can cover them, as long as any differences at a particular location are identified.
- How to conduct a risk assessment
- Identify risks and improve safety with a Health and Safety Risk Review for Businesses.
What the Assessment Should Cover
- Previous contents and residues. Fires and explosions have been caused by substances thought to have been removed long before. Assume that disturbing sludge, scale or slurry will release gas, fume or vapour.
- Contamination from outside. Gases and liquids can leak in from adjacent plant, gas mains, landfill or the surrounding ground. Spaces below ground can be affected by installations many metres away.
- Oxygen levels. Normal air is 20.9% oxygen. L101 warns that a relatively small reduction can impair mental ability with no warning to the senses, and that concentrations below 16% can lead to unconsciousness and death. Too much oxygen is also dangerous, because it makes clothing and other materials far more flammable.
- The shape of the space. Remote or low-lying pockets can hold poor air even after ventilation.
- Hazards from the work itself. Cleaning chemicals, welding and other hot work, including welding on the outside of the space.
- Hazards from outside. Machinery being started by mistake, materials being delivered automatically into the space, and exhaust fumes from engines and generators drifting in.
- The people. Physical build where access is tight, claustrophobia, respiratory conditions such as asthma, and the fitness to wear breathing apparatus.
- How a casualty would be rescued.
First, Avoid Entry
Where possible, the regulations require the work to be done from outside the space. Limiting entry also means making sure that members of the public, and staff who are not trained for it, cannot easily get into the work area. L101 gives these examples of working from outside:
- testing the atmosphere or sampling contents with long probes and tools
- cleaning with water jetting, steam or chemical cleaning, long-handled tools or in-place cleaning systems
- clearing blockages in silos with remotely operated flails, vibrators and air purgers
- inspecting through a sight glass, grille or porthole, or with CCTV
- remote visual inspection, but only where it gives the same results and safeguards as going in
Working in Confined Spaces: the Safe System of Work
In many cases entry is necessary to complete repairs, alterations or construction. The regulations then require a safe system of work, and emergency arrangements established before the work begins. L101 says that, to be effective, a safe system of work should be in writing, and that priority should go to removing the source of danger before deciding on precautions for entry. The main elements it lists are:
- Supervision and competence, with a competent person present where the risk calls for it
- Communications between those inside, those outside, and a way to summon help
- Testing and monitoring the atmosphere before entry and during the work, testing for oxygen first, then flammable gases, then toxic gases
- Gas purging and ventilation. Flammable gas or vapour must be purged with inert gas only, never with air
- Removal of residues
- Isolation from gases, liquids and flowing materials, and from mechanical and electrical equipment, with locks and tags
- Suitable equipment, including lighting and tools protected for use in flammable atmospheres
- Safe access and egress, with signs prohibiting unauthorised entry and a check that everyone is out before the space is closed up
- Fire prevention, control of static electricity and no smoking. See fire safety training
- Limits on working time in heat, in breathing apparatus or in very restricted spaces, with a tally system for large spaces
Three things L101 says never to do
Never add oxygen to “sweeten” the air. Oxygen enrichment can make grease and other materials ignite spontaneously.
Never use petrol-engined equipment in a confined space. Diesel engines and portable gas cylinders are nearly as hazardous and need exceptional precautions. Gas cylinders should be removed at the end of every work period.
Never wear a filtering respirator in an oxygen-deficient atmosphere. It does not supply air. In most confined spaces where respiratory protection is needed, it has to be breathing apparatus.
Protective and Breathing Equipment
So far as is reasonably practicable, the space should be made safe to work in without personal protective equipment or respiratory protective equipment. L101 treats both as a last resort, except for rescue, because they restrict movement, are heavy and add to heat stress. Where the risk assessment calls for them, understanding what equipment and clothing is required, and making sure it is used when needed and used properly, is essential. Breathing apparatus should be inspected each time before use, and atmospheric monitors calibrated and tested in line with the manufacturer’s recommendations, with records kept.
When Is a Confined Space Permit to Work Needed?
A permit to work is a formal written system, usually required where there is a reasonably foreseeable risk of serious injury in entering or working in the space. It records the checks, gas test results, time limits and authorisations before entry, and it is cancelled when the job is finished. L101 is clear that a permit is an extension of the safe system of work, not a replacement for it, and that a permit does not by itself make the job safe. HSE’s wider guidance on permits is HSG250, Guidance on permit-to-work systems. Read more in Confined Space Risks and Permit To Work.
Confined Space Emergency and Rescue Arrangements
Regulation 5 makes rescue planning a condition of entry. The arrangements must reduce the risks to the rescuers as well as to the casualty, and must include resuscitation equipment where the need for resuscitation is a likely consequence of the specified risk. L101 says the arrangements should cover rescue and resuscitation equipment, raising the alarm, safeguarding the rescuers, fire safety, control of nearby plant, first aid, liaison with the emergency services, and training.
Rescuers die too
L101 records that a major cause of death and injury in confined space incidents is ill-conceived attempts to save someone who has collapsed or stopped responding. Multiple fatalities have happened when rescuers were overcome by the same conditions. Nobody should go in after a casualty without protection against whatever caused the emergency.
You should not rely on the public emergency services. L101 says that reliance on them alone will not be enough to comply with the regulations. Your own arrangements must be in place before work starts, along with a way of calling the emergency services quickly and briefing them on the conditions inside.
- Rescue equipment often includes lifelines, lifting equipment, spare breathing apparatus sets and first aid equipment, including defibrillators. Even a strong person is unlikely to lift an unconscious casualty with a rope alone.
- Mouth-to-mouth resuscitation is not appropriate where the casualty has been exposed to toxic gas, because it puts the rescuer at risk.
- Experience shows that an opening needs to be at least 575 mm in diameter to allow access with full rescue equipment including self-contained breathing apparatus. Many existing openings are smaller, for example around 500 mm on rail tank wagons and 410 mm on road tankers, so access must be checked in advance.
- L101 recommends that people should not normally enter sewers smaller than 0.9 m high by 0.6 m wide.
- People with a rescue role should be trained for it, with refresher training on a regular basis, for example annually, and realistic practice drills. First aiders should be trained to deal with the foreseeable injuries.
- Some incidents are reportable under RIDDOR.
Who Needs Confined Space Training?
Training is essential for everyone who works in confined spaces, and in industries such as water and utilities, telecoms, energy and construction it is a core part of the health and safety training programme. L101 says workers must have adequate training and experience in the particular work involved, and that training should cover, as a minimum:
- an awareness of the Confined Spaces Regulations, and in particular the need to avoid entry unless it is not reasonably practicable to do so
- an understanding of the work to be done, the hazards and the necessary precautions
- an understanding of safe systems of work, including permits to work where they apply
- how emergencies arise, the need to follow the prepared emergency arrangements, and the dangers of not doing so
Depending on the role, it may also cover the use of atmospheric testing equipment and what to do with the readings, breathing apparatus and escape sets, other protective equipment, and the communication methods used inside the space. L101 does not set a fixed refresher interval for entry training. It says the frequency depends on how long it is since the person last did the work and on any changes to methods, procedures or equipment. L101 notes that regulated qualifications in confined space working and in emergency rescue are available. The main suite is City & Guilds 6160, Working in Confined Spaces, which went live in March 2021 and replaced the older 6150 qualifications. It is mapped to the National Occupational Standards and graded as low, medium and high risk. Those grades are an industry classification, not part of the regulations, and the right level follows from your risk assessment.
| If you need to… | Usual route |
|---|---|
| Give staff an awareness of confined space hazards and the law | Working in Confined Spaces (e-learning) |
| Enter low risk spaces: adequate natural or mechanical ventilation, simple unobstructed access and no likely risk of flooding | City & Guilds 6160-01 Working in Low Risk Confined Spaces |
| Enter medium risk spaces, where a specified risk is realistically expected and escape breathing apparatus is carried | City & Guilds 6160-02 Working in Medium Risk Confined Spaces |
| Enter high risk spaces, with complex access or work that needs full working breathing apparatus | City & Guilds 6160-03 Working in High Risk Confined Spaces |
| Supervise confined space work on a construction site | SSSTS – Site Supervisor Safety Training Scheme |
| Manage a site where confined space work takes place | SMSTS – Site Management Safety Training Scheme |
| Compare every confined space course and date | All Confined Spaces training courses |
Tools
See our health, safety and construction tools for help with planning and recording your health and safety arrangements.
Confined Spaces FAQs
What are the confined space regulations in the UK?
The Confined Spaces Regulations 1997 (SI 1997/1713), which came into force on 28 January 1998 and apply across Great Britain. Northern Ireland has its own equivalent regulations. They require employers and the self-employed to avoid entry to confined spaces where reasonably practicable, to follow a safe system of work where entry is unavoidable, and to have emergency rescue arrangements in place before work starts. HSE’s Approved Code of Practice L101 explains how to comply.
What is a confined space in UK law?
Under the Confined Spaces Regulations 1997 it is any place, such as a chamber, tank, vat, silo, pit, trench, pipe, sewer, flue or well, that is substantially enclosed and where there is a reasonably foreseeable risk of serious injury from fire or explosion, loss of consciousness, asphyxiation or drowning. Both parts of the test must be met.
What are the five specified risks?
Serious injury from fire or explosion; loss of consciousness from a rise in body temperature; loss of consciousness or asphyxiation from gas, fume, vapour or lack of oxygen; drowning from a rise in the level of liquid; and asphyxiation or entrapment by a free-flowing solid such as grain, sand or flour.
Does a confined space have to be small?
No. HSE’s L101 says a confined space is not necessarily small, difficult to work in or hard to get out of. A large grain silo or a ship’s hold is a confined space. A cramped loft with no specified risk is not, although it still needs a risk assessment under other regulations.
Is a trench or excavation a confined space?
It can be. Trenches and excavations are named in the regulations and in L101, but only where a specified risk is reasonably foreseeable, for example gas from contaminated ground, exhaust fumes from nearby plant settling in the excavation, or flooding. The risk of the sides collapsing is dealt with under construction law, not the Confined Spaces Regulations.
Is a permit to work a legal requirement for confined space work?
The regulations require a safe system of work. L101 says a permit to work is usually required where there is a reasonably foreseeable risk of serious injury, and that a decision not to use one should be taken by a competent person. A permit is unlikely to be needed where the risks are easily controlled, the system of work is very simple and other work nearby cannot affect the space.
How often should confined space training be refreshed?
The regulations and L101 set no fixed interval for entry training. L101 says it depends on how long it is since the person last did the work and on changes to methods, procedures or equipment. For people with a rescue role, L101 suggests refresher training on a regular basis, for example annually. In practice most employers and clients, particularly in the water industry, expect confined space certificates to be renewed every three years.
Can we rely on the fire and rescue service for confined space rescue?
No. L101 says reliance on the emergency services alone will not be sufficient to comply with the regulations. Your own rescue arrangements must be in place before anyone enters. You should still be able to call the emergency services quickly, and it can be worth notifying them in advance of prolonged or higher-risk work.
Do the Confined Spaces Regulations apply in mines?
Not below ground. The regulations do not apply below ground in a mine, to diving projects covered by the Diving at Work Regulations 1997, or to the normal shipboard activities of a sea-going ship’s crew. Separate legislation covers each of those.
Does Envico carry out confined space work or rescue?
No. Envico is an independent training intermediary. We help you compare and book accredited confined space training from approved providers. We do not carry out confined space entry, atmospheric monitoring or rescue cover.
Other Courses
Related Guidance
Sources and Further Reading
- Confined Spaces Regulations 1997 (legislation.gov.uk)
- HSE L101: Safe work in confined spaces, Approved Code of Practice (third edition, 2014)
- HSE INDG258: Confined spaces, a brief guide to working safely
- HSE HSG250: Guidance on permit-to-work systems
General guidance only, reviewed September 2026 against the Health and Safety at Work etc. Act 1974, the Confined Spaces Regulations 1997 and HSE’s Approved Code of Practice L101 Safe work in confined spaces (third edition, 2014), HSE leaflet INDG258(rev1) and City & Guilds’ published information on the 6160 qualifications. It is not a substitute for a site-specific risk assessment by a competent person. Envico is an independent training intermediary and is not affiliated with the HSE.