Monday Tech Talk – Confined Space Work in Manholes

Working in manholes is one of the most high-risk activities in the built environment. While the opening may look simple from the surface, what lies below is a confined space filled with invisible, unpredictable, and potentially fatal hazards. Toxic gases, oxygen depletion, engulfment, structural failure — these dangers can escalate in seconds.

This article explores the realities of confined space work, the mandatory controls required before entering a manhole, and the life-saving rescue procedures that every team must be prepared for.

What Makes a Manhole a Confined Space?

Confined spaces are defined by three key characteristics:

• Not designed for continuous human occupancy
• Restricted entry and exit
• Elevated atmospheric and physical risk

Manholes meet all these criteria. Unlike open workspaces, conditions inside a manhole can change rapidly, and hazards often cannot be detected without specialised equipment.

The primary hazard categories include:

1. Atmospheric Hazards

These are invisible but often deadly:

• Oxygen deficiency or enrichment — too little oxygen leads to asphyxiation; too much increases explosion risk.
• Toxic gases — hydrogen sulphide, carbon monoxide, and carbon dioxide can accumulate.
• Flammable or explosive gases — methane and other vapours can ignite from a spark or hot work.

Atmospheric testing is therefore non-negotiable.

2. Physical and Environmental Hazards

More visible, but equally dangerous:

• Falling objects such as tools or covers
• Engulfment by water, sewage, or collapsing soil
• Structural instability of ladders, steps, or walls
• Electrical or chemical exposure
• Biological hazards from sewage or contaminated water

Inside a manhole, even the walls and floor can become hazards if conditions shift unexpectedly.

Mandatory Safety Procedures: The “No Permit, No Entry” Rule

Before anyone enters a manhole, the first step is simple: justify entry. If the work can be completed from the surface, human entry is unnecessary and should be avoided.

If entry is required, a formal permit-to-work system must be followed.

Before Entry

• A trained entry supervisor completes and authorises the permit.
• Pipelines and ducts are isolated using blanks or vetter bags.
• Safety Data Sheets are reviewed for potential hazardous substances.
• A full risk assessment is conducted by a competent person.
• Atmospheric testing confirms oxygen levels (19.5%–23.5%) and checks for toxic or flammable gases.
• Gas detectors must operate continuously during entry.

If any condition is unsafe, entry is prohibited.

Entry Procedures: Setting Up the Safety Net

Once the space is declared safe, strict controls guide the entry process:

• Rescue tripod and retrieval system — workers must wear full-body harnesses attached to lifelines.
• Trained attendant — remains outside, monitors the entrants, and never enters under any circumstance.
• Reliable communication — via radios or line-of-sight methods.
• PPE — including hard hats, gloves, goggles, protective clothing, intrinsically safe lighting, and non-sparking tools.

These precautions ensure that if conditions deteriorate, workers can be removed quickly and safely.

Exit and Decontamination

After completing the task:

• Workers exit using ladders or retrieval systems
• A headcount confirms all personnel are safely out
• Tools and equipment are cleaned and decontaminated to prevent cross-contamination

Simple steps, but critical for preventing injury and maintaining accountability.

Emergency and Rescue Procedures

Confined space emergencies escalate rapidly. A standby rescue capability is therefore required before anyone enters.

Typical triggers include:

• Gas alarms
• Loss of consciousness
• Structural collapse
• Flooding
• Equipment malfunction

A rescue team must have both training and fully functional equipment ready at all times.

The Three Types of Rescue

1. Self-Rescue

The safest option — the worker recognises the danger and exits immediately (e.g., gas alarm sounds).

2. Non-Entry Rescue (External Rescue)

The standby attendant uses the tripod and winch to retrieve a worker without entering the space.

3. Entry Rescue

The highest-risk method. Specially trained rescue personnel enter the manhole using SCBA and lifelines to extract the victim. This is only performed when no other option exists.

Essential Safety Equipment

A confined space rescue kit must include:

• Tripod and winch
• Full-body harness
• Wristlets or retrieval straps
• Rescue ropes and pulleys
• Multi-gas detectors
• Intrinsically safe lighting

This equipment is lifesaving — and required for compliance.

Manholes are dangerous, unpredictable confined spaces. Safe entry requires strict compliance with procedures, continuous atmospheric monitoring, and trained personnel ready to respond to emergencies at a moment’s notice.

The message is simple: no shortcut is worth a life. With preparation, vigilance, and the right systems in place, confined space work can be performed safely and confidently.