---
title: "Confined Space Entry Safety Construction | AVANORTH"
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description: "Confined space safety guide for construction: atmospheric hazards, entry procedures, monitoring, rescue planning, and Ontario regulatory requirements."
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"og:title": "Confined Space Entry Safety Construction"
"twitter:description": "Confined space safety guide for construction: atmospheric hazards, entry procedures, monitoring, rescue planning, and Ontario regulatory requirements."
"twitter:title": "Confined Space Entry Safety Construction"
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AVANORTH Home
**Safety**·April 2, 2026· 4 min read
# **Confined Space Entry Safety for Construction Workers**
Confined spaces on construction sites include manholes, tanks, trenches, and partially completed buildings. Understanding atmospheric hazards, entry procedures, and rescue planning is essential to preventing fatalities.
**AVANORTH Team**
AVANORTH Construction
Confined spaces are among the deadliest hazards in construction. A confined space is any enclosed or partially enclosed area that is not designed for continuous human occupancy, has limited entry/exit, and may contain or develop a hazardous atmosphere. In Ontario, confined space fatalities typically involve atmospheric hazards (oxygen deficiency, toxic gases, or flammable atmospheres). The most dangerous aspect is that these hazards are often invisible.
> **Statistic:** More than 60% of confined space fatalities involve would-be rescuers who entered without proper training or equipment. The impulse to save a co-worker is understandable but entering a confined space without atmospheric monitoring and rescue equipment turns one victim into two or more.
---
## Common Confined Spaces in Construction
| Space | Hazards | Examples of Atmospheric Danger |
| --- | --- | --- |
| Manholes / utility vaults | Oxygen deficiency, toxic gases, flooding | H2S from sewers, CO from nearby engines |
| Tanks and vessels | Toxic residues, oxygen deficiency | Residual chemicals, nitrogen purge |
| Deep trenches | Oxygen displacement, cave-in | Heavier-than-air gases settle in depth |
| Crawl spaces | Limited ventilation, gas accumulation | Radon, CO from adjacent furnaces |
| Partially completed buildings | CO from equipment, poor ventilation | Gas-powered equipment exhaust |
| Pipe systems | Residual chemicals, O2 deficiency | Nitrogen purge, chemical residue |
---
## Atmospheric Hazards
### The Three Killers
1. **Oxygen deficiency:** Normal air is 20.9% oxygen. Below 19.5% is dangerous. Below 16%, impaired judgment. Below 6%, death in minutes. Caused by displacement (nitrogen, CO2), consumption (rusting, bacterial action), or absorption.
2. **Toxic gases:** Hydrogen sulphide (H2S), carbon monoxide (CO), methane, ammonia, and chemical vapours. Many are odourless or overwhelm the sense of smell at dangerous concentrations.
3. **Flammable atmosphere:** Methane, gasoline vapour, and other flammable gases or vapours. Explosive when concentration is between the Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL).
| Gas | OEL (Ontario) | IDLH | Properties |
| --- | --- | --- | --- |
| Hydrogen sulphide (H2S) | 10 ppm (TWA) | 100 ppm | Rotten egg smell (deadens at high conc.) |
| Carbon monoxide (CO) | 25 ppm (TWA) | 1,200 ppm | Odourless, colourless, tasteless |
| Methane (CH4) | LEL 5% | Explosive | Odourless, lighter than air, displaces O2 |
| Carbon dioxide (CO2) | 5,000 ppm | 40,000 ppm | Heavier than air, accumulates in low areas |
---
## Entry Procedures
### Before Entry
1. **Confined space assessment:** Identify all confined spaces on the project and classify them
2. **Hazard identification:** Determine what hazards exist or could develop
3. **Entry plan:** Written plan specifying procedures, PPE, monitoring, ventilation, and rescue
4. **Entry permit:** Signed by a competent person authorizing the entry. Specifies: location, purpose, entrants, attendant, atmospheric levels, equipment, and time limits.
### During Entry
- **Continuous atmospheric monitoring:** 4-gas monitor (O2, LEL, CO, H2S) running continuously. Pre-entry readings at top, middle, and bottom of the space.
- **Ventilation:** Mechanical ventilation to maintain safe atmosphere. Do not rely on natural ventilation alone.
- **Attendant:** A trained attendant stationed at the entry point at all times. The attendant monitors conditions, maintains communication, and initiates rescue if needed. The attendant never enters the space.
- **Communication:** Continuous communication between entrant and attendant (visual, voice, or radio).
- **Rescue equipment:** Non-entry rescue equipment (retrieval system with mechanical winch) ready for immediate use.
> **The Attendant Rule:** The attendant's sole job is to monitor the entry and call for rescue if something goes wrong. The attendant must resist the urge to enter the space to help. Entering without proper equipment creates additional victims. This is the hardest rule to follow and the most important.
---
## Rescue Planning
| Rescue Type | Method | When Used |
| --- | --- | --- |
| Non-entry rescue (preferred) | Retrieval system (tripod + winch + harness) | Vertical entry (manholes, tanks) |
| Entry rescue (last resort) | Trained rescue team enters with SCBA | Horizontal spaces, complex geometry |
| Emergency services | Fire department confined space rescue team | Backup to on-site rescue |
Key rescue planning requirements:
- Rescue must be available before entry begins, not planned after an incident
- Non-entry rescue equipment must be set up and tested before entry
- If entry rescue is the plan, the rescue team must be on site, trained, and equipped
- Emergency services must be notified of the entry and the space location
- Practice rescue drills at least annually
> **AVANORTH Policy:** No confined space entry on any AVANORTH project occurs without a signed entry permit, continuous atmospheric monitoring, a trained attendant, and a rescue plan tested before entry. Every worker who may enter a confined space receives specific training. We have a zero-incident target for confined space work because the margin for error is zero.
#confined-space #safety #atmospheric-hazards
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