Definition and Identification of Confined Spaces; Classification and Risk Assessment
This domain tests the legal definition of a confined space, how to identify one on a real site, and how to classify and assess the risk before any entry.
The legal definition
A confined space is any place such as a chamber, tank, vat, silo, pit, trench, pipe, sewer, flue, well or similar space which, by virtue of its enclosed nature, gives rise to a reasonably foreseeable specified risk. The five specified risks are:
- fire or explosion from flammable gas, vapour or dust, or from oxygen enrichment;
- loss of consciousness from an increase in body temperature;
- loss of consciousness or asphyxiation from gas, fume, vapour or lack of oxygen;
- drowning from an increase in the level of liquid;
- asphyxiation from a free-flowing solid, or entrapment from collapse of walls or floor.
The definition turns on the risk, not the name. A 1.5 m excavation can be a confined space if fumes can accumulate; a large room can be one if inert gas can enter.
Identification and register
- Survey drawings, drains, ducts, pits, sumps, manholes, silos, tanks, boilers and sewers.
- Mark access points with warning signs and keep a register of location, hazards, access and isolation points.
- Re-survey after modifications or a change of process.
Classification and risk assessment
The competent person identifies hazards, evaluates risk by severity and likelihood, and selects controls using the hierarchy: avoid entry, then engineering controls, then administrative controls, with PPE last. Consider the atmosphere before and during the task; residues and sludge; adjacent plant and services; the work itself (hot work, jetting, painting); access and egress; number of entrants; rescue; competence and duration. Record the assessment and review it when conditions change, after an incident, and periodically.
Worked example
A manhole receives flow from a food factory. A test at the top shows 20.9% oxygen, 0% LEL and 0 ppm H2S. The task is high-pressure jetting of grease. Reasoning: jetting disturbs sludge and can release hydrogen sulphide in bursts; the reading at the top does not represent the working level; the space is high hazard and needs continuous monitoring at the point of work, forced ventilation, BA on standby, a rescue plan and a permit. One reading is not a risk assessment.
Traps that cost marks
- "It's a trench, not a confined space" - the specified risk decides.
- Assuming an open top means good ventilation.
- Failing to review the assessment when the task or sludge depth changes.
- Ignoring hazards entering from connected plant, such as backflow or gas migration.