A confined space is an enclosed or partially enclosed area that is not designed for continuous human occupancy, has limited means of entry and exit, and lacks adequate natural ventilation. In the construction industry, confined spaces represent one of the most hazardous working environments. Every year, serious and sometimes fatal accidents occur because the risks associated with these spaces are underestimated.
Examples of confined spaces
Confined spaces are found on virtually every construction site and in many existing structures:
- Crawl spaces beneath buildings
- Tanks and silos in industrial facilities
- Manholes and sewer chambers in civil engineering works
- Lift shafts during construction or maintenance
- Basements and cellars without mechanical ventilation
- Service ducts and risers in commercial buildings
- Closed formwork during concrete pours
- Attic spaces with restricted access
Hazards
Working in a confined space introduces specific dangers that do not exist in open environments:
- Oxygen deficiency — oxygen levels may fall below the safe threshold of 19.5%, leading to loss of consciousness or death
- Toxic gases — substances such as hydrogen sulphide (H2S), carbon monoxide (CO), or methane can accumulate without visible or noticeable warning signs
- Fire and explosion risk — flammable gases or vapours can reach dangerous concentrations in an enclosed area
- Entrapment — restricted movement increases the risk of becoming trapped or being unable to escape quickly
- Engulfment — free-flowing solids or liquids may suddenly enter the space
Required safety measures
In the UK, the Confined Spaces Regulations 1997 set out clear legal requirements. Similar frameworks exist in other countries (e.g., OSHA in the US). Key measures include:
- Risk assessment before any work begins
- Continuous gas monitoring using a multi-gas detector (minimum O2, LEL, CO, and H2S)
- Forced ventilation to maintain a safe, breathable atmosphere
- Standby person — a trained individual stationed outside the space to monitor conditions and raise the alarm
- Rescue plan and equipment immediately available on site
- Permit-to-work system — a formal written authorisation process before anyone enters the space
- Training — all workers must have completed an approved confined space entry course
Related terms
- Gas detection
- Standby person
- Permit to work
- Risk assessment
- Personal protective equipment (PPE)
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