On this page
- Why confined-space hazards change
- Atmospheric hazards
- Engulfment and material flow
- Hazardous energy and connected systems
- Access, falls and restricted movement
- Heat, cold and physical workload
- Hazards created by the work
- Human factors and coordination
- Rescue is a control, not an afterthought
- Questions for the competent assessment
- Minimum evidence an employer should retain
- Official source
Quick answer
Assess the space, the work and the conditions that can change
Confined spaces can combine hazards that are difficult to see, measure or escape. A worker may enter a space that appears safe and then be exposed to oxygen loss, toxic gas, moving equipment, engulfment or heat created by the work itself.
Alberta employers must assess the actual space and planned work. Part 5 of the Occupational Health and Safety Code requires a written code of practice, competent hazard assessment, training, an entry permit, atmospheric testing where required, effective rescue arrangements and other controls.
Why confined-space hazards change
Conditions inside a space may be affected by connected equipment, process residue, weather, nearby vehicles, cleaning agents, welding, coatings, biological activity or ventilation failure. A reading taken before entry does not guarantee that the atmosphere will remain safe.
The assessment should consider routine conditions, the work to be performed, simultaneous operations and reasonably foreseeable failures. Review the assessment whenever the scope, crew, equipment, process or environment changes.
Atmospheric hazards
Oxygen deficiency or enrichment
Low oxygen can result from rusting, combustion, inert-gas displacement or biological activity. Oxygen enrichment increases fire risk. Alberta OHS Code s. 52 requires oxygen to be maintained between 19.5% and 23.0%.
Test with a suitable calibrated instrument before entry and at the locations where workers will be present. Continue monitoring at the frequency required by the assessment; continuous monitoring may be needed when conditions are unpredictable.
Toxic contaminants
Hydrogen sulphide, carbon monoxide, solvent vapours, welding fumes and process gases may accumulate. The specific contaminants and exposure limits must be identified from the process, safety data sheets, previous measurements and competent assessment. Generic four-gas monitoring may not detect every contaminant.
Use elimination, isolation, cleaning, purging and ventilation as appropriate. Respiratory protection must be selected and used under the applicable Alberta requirements and a site-specific respiratory protective equipment program.
Flammable or explosive atmospheres
Vapours, gases or dusts may ignite. Control sources, verify isolation, use appropriately rated equipment and monitor the atmosphere. Stop work when readings approach the limits set by the applicable legal requirement, equipment specification or approved procedure.
Engulfment and material flow
Grain, sand, water, slurry and other free-flowing material can trap or suffocate a worker. Material may bridge, form unstable surfaces or release without warning.
Prevent entry where possible. Isolate and secure all inflows and discharge equipment. Do not rely on a worker standing on the material or on a harness alone to control engulfment risk.
Hazardous energy and connected systems
Mixers, augers, conveyors, valves, dampers, pressure systems and mobile equipment can move or release energy into the space. Section 49 addresses hazardous substances and energy that could endanger a worker.
Identify every energy source and connection. Apply the energy-control requirements, equipment-specific isolation procedures, approved engineering and manufacturer instructions. Verify the isolation before entry and maintain control until the space is cleared and the permit is closed.
Access, falls and restricted movement
Narrow openings, ladders, obstructions and vertical entry can make normal movement and emergency removal difficult. Consider:
- safe access and egress under s. 57;
- fall protection where the Alberta fall-protection requirements apply;
- the size of the worker and protective equipment;
- lighting, visibility and communication;
- how an injured or unconscious worker will be removed; and
- whether equipment blocks the rescue route.
Entry equipment and rescue equipment must work together. A tripod or winch is not automatically suitable for every opening, worker position or rescue path.
Heat, cold and physical workload
Protective clothing, poor air movement and physically demanding work can increase heat strain. Cold surfaces, water and weather exposure can create cold stress. The assessment should consider work-rest arrangements, hydration, acclimatization, monitoring and emergency response appropriate to the conditions.
Fatigue and restricted posture can also affect judgement and self-rescue. Set realistic entry durations and rotate work where needed without introducing untrained personnel.
Hazards created by the work
The planned task may create the most serious hazard. Examples include:
- welding or cutting that consumes oxygen and generates fumes;
- coating or cleaning that releases vapours;
- pressure washing that introduces water, noise and restricted visibility;
- electrical tools used in wet conditions;
- combustion equipment producing carbon monoxide; and
- work that blocks access or alters ventilation.
Update the permit and controls when the task changes. Do not allow “small additional work” to proceed outside the assessed scope.
Human factors and coordination
Confined-space controls depend on people recognizing changes and responding quickly. Consider language and literacy needs, worker experience, medical limitations, fatigue, supervision and contractor coordination.
Where multiple employers are involved, define who controls the space, authorizes entry, verifies isolation, performs testing, provides rescue and stops the work. Confirm these roles in writing and in the pre-entry discussion.
Rescue is a control, not an afterthought
Section 55 requires effective rescue and emergency procedures. The rescue plan must match the hazards, access route and likely casualty condition. It must identify trained personnel, equipment, communication and response time.
A tending worker should not enter impulsively. Many multiple-fatality events occur when an unprotected person attempts rescue. The tending worker must initiate the planned response and enter only if separately trained, equipped and authorized for that role.
Questions for the competent assessment
- Can the work be completed without entry?
- What makes the space confined or restricted under Alberta’s definitions?
- What materials, residues and connected systems are present?
- What could change the atmosphere during the work?
- Which contaminants must the instrument detect?
- How will each energy source and material flow be isolated and verified?
- What communication method will work in the actual conditions?
- What would require workers to leave immediately?
- How will rescue personnel reach and remove the worker?
- Has the rescue method been practised under representative conditions?
Minimum evidence an employer should retain
- space classification and competent hazard assessment;
- current code of practice and related procedures;
- entry permits and atmospheric test records;
- instrument calibration and bump-test information;
- training and competency records;
- isolation and equipment inspection records;
- rescue plans, equipment inspections and drill records; and
- corrective actions and verification of effectiveness.
Alberta OHS Code s. 58 specifies retention requirements for confined-space records. Confirm the period that applies to the entry and any longer contractual or organizational requirement.
Official source
Alberta Occupational Health and Safety Code, Part 5 — Confined Spaces, including ss. 44–58.
Source verification date: November 6, 2026. This draft requires CRSP review and site-specific verification before publication.
John Duplessis, B.Sc., CRSP
This draft remains subject to the author’s professional review and approval before publication.
