8.3 Safe Working in Confined Spaces

Types of confined spaces and why they are dangerous

Definitions differ by jurisdiction. Under HSE guidance, a confined space is an enclosed or largely enclosed place where specified serious risks are reasonably foreseeable, such as oxygen deficiency, toxic or flammable atmospheres, drowning or engulfment. Lack of normal occupancy or restricted access alone does not establish the British definition.

It can be any enclosed space where there is a risk of death or serious injury from hazardous substances or dangerous conditions, such as lack of oxygen.

Confined spaces can be found in almost any workplace, and they can be below or above ground. Despite the name, a confined space is not necessarily small. Some examples:

• storage tanks
• silos
• reaction vessels
• enclosed drains
• sewers
• open-topped chambers
• combustion chambers in furnaces
• ductwork

It is not possible to give a complete list. Some places become confined spaces when work is carried out in them, or during their construction, fabrication or later modification.

Working in a confined space is dangerous because of noxious fumes, reduced oxygen or the risk of fire. Other dangers include flooding and drowning, or suffocation from another source such as dust, grain or some other contaminant.

The main hazards and risks of working in a confined space

Confined spaces are dangerous because of the number of hazards that may be present:

• a lack of oxygen
• poisonous gas, fume or vapour
• liquids and gases that can suddenly fill the space, or release gases into it, when disturbed
• free-flowing solids such as grain, which can partly solidify or bridge in silos, causing blockages that can collapse without warning
• fire and explosion, for example from flammable vapours or excess oxygen
• residues left in tanks and vessels, or remaining on internal surfaces, which can give off gas, fume or vapour
• dust in high concentrations, for example in flour silos
• hot conditions that cause a dangerous rise in body temperature
• restricted access. Confined spaces can be hard to get into, which makes escape difficult and hinders emergency rescue. Once inside, there may be no quick or easy way out

Some of these conditions may already be present in the space. Others may arise from the work itself, or from ineffective isolation of nearby plant, such as a leak from a pipe connected to the space. The enclosure and the limited working room can also make other dangers from the work worse. For example:

• machinery in use may need special precautions, such as dust extraction for a portable grinder, or special precautions against electric shock
• gas, fume or vapour can arise from welding or from the use of volatile and often flammable solvents, adhesives and so on

Summary notes for Element 8 · Cheat sheet · Glossary. A study aid, not published or endorsed by NEBOSH.