How OSHA's confined-space rule works in construction
Confined-space work in construction is governed by 29 CFR 1926 Subpart AA (the “Confined Spaces in Construction” standard, 1926.1201–1926.1213). It is a separate standard from the general-industry rule at 29 CFR 1910.146 — citing 1910.146 on a construction permit is one of the most common mistakes inspectors flag, so this permit headers itself with the construction standard. A space is permit-required the moment it can contain a hazardous atmosphere, an engulfment hazard, an entrapment configuration, or any other recognized serious hazard (1926.1202).
Pre-entry atmospheric acceptance values
Test the atmosphere from outside the space, in order — oxygen, then combustibles, then toxics (1926.1204(e)) — and authorize entry only when every reading is acceptable. The calculator above applies exactly these rules and refuses to produce an “entry authorized” permit when any reading is out of range or missing.
| Gas | Acceptable (entry) | Basis | Citation |
|---|---|---|---|
| Oxygen (O₂) | 19.5–23.5% | 1926.1202 hazardous-atmosphere definition | 29 CFR 1926.1202 |
| Combustible gas (LEL) | < 10% of LFL | 1926.1202 — a flammable atmosphere in excess of 10% LFL is hazardous (the tool alarms at 10%, a step earlier than the definition) | 29 CFR 1926.1202 |
| Carbon monoxide (CO) | < 25 ppm (tool trigger) | 4-gas alarm setpoint, below the 50 ppm construction PEL (1926.55 Table 1) | 29 CFR 1926.55 Table 1 |
| Hydrogen sulfide (H₂S) | < 10 ppm (tool trigger) | 10 ppm construction PEL, 1926.55 Table 1 (NIOSH 10-min ceiling REL is the same) | 29 CFR 1926.55 Table 1 |
The H₂S figure is not a recommendation: 10 ppm is the construction limit itself, 29 CFR 1926.55 Table 1, and NIOSH sets the same 10 ppm as a 10-minute ceiling — which is what a pre-entry reading measures. The 20 ppm ceiling is Table Z-2, general industry, and does not govern construction work. CO alarms at 25 ppm, deliberately below the 50 ppm construction PEL. Continuous atmospheric monitoring is required throughout the entry (1926.1204(e)).
The three required roles
| Role | Responsibility | Citation |
|---|---|---|
| Entry Supervisor | Authorizes entry, verifies acceptable conditions, signs and terminates the permit. | 29 CFR 1926.1210 |
| Attendant | Stays OUTSIDE the space at all times, monitors entrants, keeps communication, initiates rescue. | 29 CFR 1926.1209 |
| Authorized Entrant | Performs the work; knows the hazards; exits immediately when ordered or on any alarm. | 29 CFR 1926.1208 |
Worked examples
Example 1 — Manhole entry, acceptable atmosphere. A crew enters Manhole B to repair a conduit. Pre-entry 4-gas readings: O₂ 20.9%, LEL 0% of LFL, CO 4 ppm, H₂S 1 ppm. All four are within the acceptable band, so the permit prints “READINGS WITHIN LIMITS” — and says in the same breath that the entry supervisor’s signature is what authorizes entry, not four numbers (1926.1205(b)). The crew names a supervisor, an attendant who stays at the opening, and one entrant; rescue is a tripod/winch retrieval system (non-entry); ventilation is a forced-air blower.
Example 2 — Tank with a toxic reading, entry blocked. A welder is about to enter Tank #3. Pre-entry readings: O₂ 20.8%, LEL 2%, CO 4 ppm, but H₂S 14 ppm. Because 14 ppm exceeds the 10 ppm trigger, the atmosphere is NOT acceptable; the tool flags H₂S specifically and refuses to authorize the permit. The correct action is to ventilate, re-test from outside, and only generate the permit once H₂S drops below the trigger. (Selecting “self-rescue” would also block the permit — a PRCS needs a non-entry retrieval system or a rescue service under 1926.1211.)
What to do next
- Before entry: confirm the written permit space program exists (1926.1204), calibrate the gas meter, and isolate/lock out energy and inflow lines feeding the space.
- During entry: keep continuous atmospheric monitoring running, keep the attendant outside and in constant communication, and stop work on any alarm.
- After entry: cancel the permit, note any problems, and retain the canceled permit for at least one year to review your program (1926.1205(f)).
- Bilingual crews: switch the permit to Spanish so the entrant and attendant read the same hazards, controls, and rescue plan you signed.
After the permit is printed: knowing who is inside, right now
A generated permit answers the paperwork question. It does not answer the one that matters at 2 p.m.: is anyone inside a space on this site right now, and since when? That answer lives on a clipboard next to the hatch — until the attendant is asked to help two bays over. In HazComFast, the entry permit is a live record attached to the jobsite: the moment an entry starts, the site's permit screen shows the space, the number of entrants, and the start time, and keeps showing them until the entry is closed.
The screen above the list keeps the running counts — active, completed, canceled — so a supervisor arriving on site reads the state of every permit space in one glance, filtered by jobsite. Each active entry carries its space ID, its location in plain words, its entrant count and its start time. When the entry ends, the permit moves to Completed and stays on the record — canceled permits are what 1926.1205(f) asks you to keep and review.
The free generator stays free, and the printed permit it produces is yours. The difference the platform adds is the part paper cannot do: the permit that knows whether it is currently open. See how HazComFast handles digital permits →
Frequently asked questions
What defines a confined space under OSHA?
A confined space meets ALL three criteria: (1) it is large enough for an employee to bodily enter and perform work, (2) it has limited or restricted means of entry or exit, and (3) it is not designed for continuous employee occupancy (29 CFR 1926.1202). Tanks, vessels, silos, storage bins, hoppers, vaults, pits, manholes, and tunnels are typical examples. Trenches and excavations are NOT confined spaces — they are governed by 1926 Subpart P.
What makes a confined space 'permit-required' (PRCS)?
A confined space becomes permit-required if it contains, or has the potential to contain, a hazardous atmosphere; material that could engulf an entrant; an internal configuration that could trap or asphyxiate (converging walls, inwardly sloping floors); or any other recognized serious safety or health hazard (29 CFR 1926.1202). For construction this is 29 CFR 1926 Subpart AA. 1910.146 is the general-industry analog and does not apply to construction work.
What atmospheric readings are required before entry, and in what order?
Test from outside the space, in this fixed order (29 CFR 1926.1204(e)): (1) oxygen, (2) combustible gases and vapors, then (3) toxic gases. Acceptable: O₂ 19.5–23.5%, combustibles below 10% of the LFL (29 CFR 1926.1202). For H₂S the 10 ppm this tool uses is the construction limit itself — 29 CFR 1926.55 Table 1, 8-hour TWA — and NIOSH sets the same 10 ppm as a 10-minute ceiling, which is what a pre-entry reading measures; the 20 ppm ceiling is Table Z-2, general industry, and does not govern construction work. CO alarms at 25 ppm, below its 50 ppm construction PEL.
Who are the required roles for a permit-required confined space entry?
Three roles are required (duties at 29 CFR 1926.1208–1926.1210): the Entry Supervisor authorizes entry, verifies acceptable conditions, and terminates entry; the Attendant remains OUTSIDE the space at all times, monitors entrants, maintains communication, and initiates rescue; and the Authorized Entrant performs the work, knows the hazards, communicates with the attendant, and exits immediately on order. One attendant may monitor more than one space only if the program allows it and they can effectively perform every duty.
Why isn't 'self-rescue' an acceptable rescue plan?
For a permit-required confined space, 29 CFR 1926.1211 requires the employer to provide a non-entry retrieval system (e.g., a full-body harness, retrieval line, and a tripod/winch at the opening) OR arrange for a rescue service. Relying on the entrant to climb out unassisted is not a compliant rescue plan, because the most common confined-space fatalities — oxygen deficiency and toxic gas — incapacitate the entrant before they can self-rescue. OSHA data repeatedly shows that more than half of confined-space deaths are would-be rescuers. This tool blocks a permit that names self-rescue.
Is a confined space permit valid across shifts or days?
No. An entry permit covers a single, defined entry operation and its duration may not exceed the time required to complete the assigned task identified on it (29 CFR 1926.1205(d)). It must be re-evaluated whenever conditions change, when there is an interruption, or at the start of a new shift, and the canceled permit is retained for at least one year to review the program (29 CFR 1926.1205(f)). Generate a fresh permit for each shift or each new space.
Does OSHA require a written permit space program?
Yes. If your worksite has one or more permit-required confined spaces, the employer must develop and implement a written permit space program and make it available to employees (29 CFR 1926.1204). This permit is one record produced under that program; it does not replace the program itself. State-Plan states (e.g., California, Michigan, Washington) may impose additional requirements.
Sources & verification
- OSHA — 29 CFR 1926 Subpart AA (Confined Spaces in Construction)
- eCFR — 29 CFR Part 1926, Subpart AA (full text)
Standard & thresholds verified 2026-10-05. This generator produces a permit template per 29 CFR 1926 Subpart AA — Confined Spaces in Construction (1926.1201–1926.1213) — it is not legal advice and it does not certify any specific entry as compliant. The qualified person on site is responsible for verifying conditions before authorizing entry. State-Plan states may impose additional requirements.
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