Guides
Confined space on site: prepare before entry
By Claude Piché, founder · Updated September 21, 2026
A confined space is not “a tight hole”. On a Québec jobsite it is a CSTC definition, atmosphere limits, a written rescue plan — and often lockout.
First: construction site or establishment?
On a construction site, confined space is CSTC 1.1 (17.1) and subsection 3.21. Establishments follow the RSST (including section 302 for atmosphere). Mixing the two applies the wrong LEL limit.
This guide is for the jobsite. Numeric thresholds live on the confined-space regulation sheet. Here: what does the crew do before anyone goes in?
Written identification before work
CSTC 3.21.1 requires written identification: tools, equipment, piping, hazards, contaminants, rescue means. It is not an RSST permit form.
Tie it to the confined-space checklist: PPE, ventilation, and CSTC 2.20 lockout before entering a machine danger zone. The checklist is “what now”; the legal sheet is “which article”.
Atmosphere: test, then hold
Nobody enters “to take a look”. CSTC 3.21.2 forbids entry outside the oxygen range, above the CSTC LEL fraction, or above RSST Annex I contaminants — including with a respirator. An APR does not bypass 3.21.2 on a construction site.
Readings follow 3.21.3. Continuous alarmed instruments drop the log, not the monitoring. Ventilation (3.21.4) must hold concentrations for the whole job.
Rescue: written, equipped, no improvisation
The rescue plan is 3.21.1 f). 3.21.5 keeps unassigned people away. The Code does not say “an attendant who never leaves”. A coworker jumping in without procedure is often the second victim.
Before entry: communication, rescue gear, headcount. During: evacuate on alarm. After: everyone out, access closed. The list sequences this; it does not replace training.
Energy around the hole
Many site confined spaces are also machines. Killing the motor is not CSTC 2.20. Each person with access applies a unique-key padlock.
Coordinate trades. The lockout list and the electrical list cover isolation; confined space covers atmosphere and rescue.
What the tool does not do
OK Sécurité timestamps checks. A PDF is not proof the atmosphere was good. Independent product: the CNESST does not certify these lists.
Start with the confined-space list and the CSTC 3.21 sheet. Do not enter until written identification and readings are done.
Informational guide for Québec construction SMEs. Thresholds are on the CSTC 3.21 / RSST 302 sheet. OK Sécurité is not certified by the CNESST. The official text prevails. Confirm with your prevention program. For information only — this is not legal advice. OK Sécurité is an independent company with no affiliation to the CNESST: we are not mandated, endorsed or certified by it. Where there is any discrepancy, the official text published by Légis Québec or the CNESST prevails.
Sources
Informational only. Confirm obligations with your prevention program and:
- CNESST — Mesures spécifiques pour les chantiers de construction
- Safety Code for the construction industry (CSTC) and Regulation respecting occupational health and safety (RSST)
Official rules (French)
Related checklists
Lists to open before entry:
Common questions
- Is the LEL limit 5% or 25%?
- Both, in two regulations. Jobsite: CSTC 3.21.2 (25% LEL). Establishment: RSST 302 (5%). Use the regime that applies.
- Can a respirator allow entry if oxygen is out of range?
- Not on a CSTC 3.21.2 construction site. See the confined-space sheet.
- Must an attendant never leave?
- The CSTC requires a rescue plan (3.21.1 f) and keeping unassigned people out (3.21.5). It does not write that oral slogan.
- Where to start in the app?
- Confined-space list, then lockout if a machine or energy source is involved. The demo shows the gesture without an account.