Confined spaces in residential construction

TL;DR

Confined space entry is High-Risk Construction Work (HRCW) under WHS Regulation reg 291(f), so a SWMS is mandatory before anyone goes in. On a residential build the spaces that bite are sub-floor voids with less than 900 mm clear height, enclosed water tanks, sewer pits, and roof spaces with no through-ventilation. Before entry: a competent person must complete a written risk assessment, issue a signed entry permit, test the atmosphere (oxygen 19.5% to 23.5%, flammable gas below 5% LEL), and have a rescue arrangement in place. A standby person must remain outside for the full duration. Getting this wrong and someone dies inside is a Category 1 offence under the WHS Act.

Body

What is a confined space?

Under the model WHS Regulations (Part 4.3), a confined space is an enclosed or partially enclosed space that:

is not designed or intended primarily to be occupied by a person,
is at normal atmospheric pressure while any person is in the space, and
presents a risk to health or safety from one or more of: an unsafe oxygen level, a harmful concentration of airborne contaminants, a flammable or explosive atmosphere, or engulfment.

The definition appears in the definitions section of the model WHS Regulations (adopted in NSW as Work Health and Safety Regulation 2017, Cth as Work Health and Safety Regulations 2011, and equivalent instruments in QLD, WA, SA, TAS, ACT, NT). Victoria uses equivalent provisions under the Occupational Health and Safety Regulations 2017.

Source: Work Health and Safety (Confined Spaces) Code of Practice 2015, approved under WHS Act s 274, legislation.gov.au (verified 2026-05-10).

The three-part test on a residential site

A space qualifies as a confined space only if it meets all three elements. Most residential spaces meet the first two easily. The third is the practical question:

Sub-floor void below a suspended floor: restricted entry, typically low clearance, risk of oxygen depletion from organic soils or methane from decomposition. Commonly a confined space when clearance is below 900 mm and the space is enclosed on all sides.
Enclosed water tank or rainwater tank: oxygen can be depleted by internal coatings or microbial activity. Entry to clean or repair is a confined space entry.
Sewer pit or stormwater inspection shaft: hydrogen sulfide (H2S) is the primary hazard; can accumulate to lethal concentrations without warning. Almost always a confined space.
Roof cavity with no through-ventilation: if the space is enclosed (sarked, insulated batts on all sides) and has no adequate natural ventilation, it may qualify, particularly where off-gassing from insulation products or residual chemical treatments exists.
Under-slab service chambers and confined drainage channels: treated as confined spaces if meeting all three criteria.

Spaces with a door at ground level allowing quick, unobstructed exit (for example, a walk-in cool room or a plant room with cross-ventilation and clear egress) are generally not confined spaces. The test is always applied to the actual conditions at the time of entry, not to a general category.

Source: Work Health and Safety (Confined Spaces) Code of Practice 2015 (verified 2026-05-10).

HRCW classification and SWMS obligation

Work in or near a confined space is item 6 on the model HRCW list (WHS Regulation reg 291(f)). This means:

A SWMS must be prepared before the work starts.
The SWMS must identify the confined space hazards and specify the controls.
Workers must comply with the SWMS while work is being carried out.
The SWMS must be reviewed and revised if conditions change.

The SWMS does not replace the entry permit. Both documents are required: the SWMS covers the overall work method and controls; the entry permit authorises entry for a specific space at a specific time.

Source: Work Health and Safety Regulation 2017 (NSW) reg 291(f) and regs 293 to 300 (verified 2026-05-10).

Risk assessment

Before any confined space entry, a PCBU must ensure a competent person carries out and records a written risk assessment. The risk assessment must identify:

All hazards present (atmospheric, physical, biological, engulfment)
The likelihood and consequence of each hazard
Control measures, including isolation, ventilation, atmospheric monitoring, and PPE
Communication and rescue arrangements, including PPE

The entry permit can serve as the written record of the risk assessment provided it captures all the required elements.

Source: Work Health and Safety (Confined Spaces) Code of Practice 2015 (verified 2026-05-10).

Entry permit requirements

Under the WHS Regulations (Part 4.3), an entry permit is required before any person enters a confined space. The permit must be issued by a competent person and must specify:

The space to which the permit relates (identified uniquely)
The names of the persons authorised to enter, and the time period
The results of atmospheric testing and the control measures based on the risk assessment
Isolation procedures and any ventilation controls in place
PPE required
Communication arrangements and emergency procedures
The sign-in and sign-out record

One permit covers one space. A new permit is required for each entry, including re-entry after the space has been vacated. The permit must be displayed prominently at the entry point. Records must be kept for 30 days after completion of the work, or for at least 2 years if a notifiable incident occurs.

Source: Work Health and Safety (Confined Spaces) Code of Practice 2015 (verified 2026-05-10); WorkSafe WA, WHS duties on managing the risks of working in confined spaces (verified 2026-05-10).

Atmospheric monitoring

AS/NZS 2865:2009 and the WHS Regulations set the atmospheric standards for confined space entry.

Safe atmosphere thresholds:

Parameter	Safe range / limit
Oxygen content	19.5% to 23.5% by volume
Flammable gas / vapour	Below 5% of Lower Explosive Limit (LEL)
Toxic contaminants	Below the relevant Workplace Exposure Standard (WES)

If flammable gas reaches 5% LEL, workers must evacuate immediately. Continuous monitoring during work is required where the atmosphere may change. Testing must occur before entry (pre-entry test establishes permit conditions) and monitoring must continue throughout the entry period.

The distinction matters: atmospheric testing is a short-term measurement before entry; atmospheric monitoring is continuous measurement during the work. Both are required where atmospheric hazards are present or cannot be ruled out.

Source: AS/NZS 2865:2009 (Safe Working in a Confined Space); model WHS Regulations Part 4.3; f7i.ai Confined Space Gas Testing Requirements Australia 2026 Guide citing WHS Regulations and AS/NZS 2865:2009 (verified 2026-05-10).

Rescue arrangements

A rescue arrangement must be in place before anyone enters. The key requirements are:

Standby person: a competent person must be stationed outside the confined space for the entire duration of the entry. The standby person must maintain continuous communication with entrants, never enter the space themselves (even in an emergency), and summon rescue if needed.
Non-entry rescue preferred: rescue by tripod, winch, and retrieval line from outside the space is the preferred method. It avoids putting rescuers at risk.
Rescue equipment pre-staged: harnesses, tripods, winches, respiratory protective equipment (RPE), and first-aid equipment must be in position before entry begins, not retrieved during an emergency.
Practised emergency procedures: rescue procedures must be documented, trained, and rehearsed. An untested rescue plan is not a rescue plan.

Entry rescue (a rescuer physically entering) requires trained confined space rescue personnel with appropriate RPE and is a last resort.

Source: Work Health and Safety (Confined Spaces) Code of Practice 2015; WorkSafe WA (verified 2026-05-10).

Isolation and ventilation

Before entry, all energy sources affecting the space must be isolated: electrical, mechanical, hydraulic, pneumatic, gravity. Pipes and ducts that could introduce contaminants must be physically blanked off, not just valve-closed.

Natural ventilation is the preferred control for atmospheric hazards. Where natural ventilation is insufficient, forced mechanical ventilation must be used to maintain a safe atmosphere before and during entry. Purging (continuous ventilation to displace contaminants before entry) is often required for sewer pits and enclosed tanks.

Victoria: OHS Regulations 2017

Victoria uses the Occupational Health and Safety Act 2004 (Vic) and OHS Regulations 2017 (Vic). The confined space provisions sit in Part 3.4 of the OHS Regulations and apply equivalent duties to those under the model WHS Regulations. The practical requirements for entry permits, atmospheric monitoring, and rescue arrangements are substantively the same.

What can go wrong

Not recognising the space as a confined space: the most common failure. A builder assumes a sub-floor void is just a crawl space. No risk assessment, no permit, no atmospheric test. If soil gas (methane, H2S) is present, the first sign is a collapsed worker.
Permit issued but atmosphere not tested: the permit is treated as paperwork rather than a live safety document. Conditions inside change between issue and entry.
Standby person leaves post: standby person steps away briefly to get tools. Entrant collapses. No one to summon help.
Rescuer enters without equipment: the single most common way a confined space incident becomes a multiple fatality. Well-intentioned rescuers entering without RPE are overcome by the same atmosphere that felled the first person.
Ventilation removed before work finishes: forced ventilation switched off partway through to reduce noise. Atmosphere deteriorates while workers are still inside.
Sewer pit assumed safe because it was safe last time: H2S concentrations are variable and can spike rapidly with temperature or disturbance. Historical safe entry is not evidence of current safe conditions.

References

Work Health and Safety (Confined Spaces) Code of Practice 2015, approved under the Work Health and Safety Act 2011 (Cth) s 274, legislation.gov.au (verified 2026-05-10)
AS/NZS 2865:2009 Safe Working in a Confined Space, Standards Australia (verified 2026-05-10)
Safe Work Australia, Model Code of Practice: Confined Spaces (July 2020), safeworkaustralia.gov.au (verified 2026-05-10)
WorkSafe WA, WHS duties on managing the risks of working in confined spaces, worksafe.wa.gov.au (verified 2026-05-10)
Work Health and Safety Regulation 2017 (NSW) reg 291(f), Part 4.3, legislation.nsw.gov.au (verified 2026-05-10)