3.5 Confined Space Entry & Permitting (OSHA 1910.146)

Confined Space Entry and Permitting

Working in confined spaces presents invisible, often rapidly fatal hazards. Oxygen deficiency, toxic gas accumulation, and engulfment are frequent causes of death in these environments. OSHA addresses these severe risks in the General Industry standard 29 CFR 1910.146 (Permit-Required Confined Spaces).

Defining a Confined Space

Not all small or tight spaces are "confined spaces" under OSHA regulations. To meet the baseline definition of a confined space, an area must meet all three of the following criteria:

1. Size: It is large enough and so configured that an employee can bodily enter and perform assigned work.
2. Access: It has limited or restricted means for entry or exit (e.g., tanks, vessels, silos, storage bins, hoppers, vaults, and pits).
3. Occupancy: It is not designed for continuous employee occupancy.

Permit-Required vs. Non-Permit Required

Once a space is deemed a confined space, the employer must evaluate it to determine if it is a Permit-Required Confined Space (PRCS). A confined space becomes permit-required if it has one or more of the following characteristics:

• It contains or has a potential to contain a hazardous atmosphere.
• It contains a material that has the potential for engulfing an entrant (e.g., grain, sand, liquid).
• It has an internal configuration such that an entrant could be trapped or asphyxiated by inwardly converging walls or by a floor which slopes downward and tapers to a smaller cross-section.
• It contains any other recognized serious safety or health hazard (e.g., exposed live electrical wires, unguarded machinery).

If a space does not contain any of these hazards, it is a non-permit confined space. However, if conditions change (e.g., introducing a chemical solvent for cleaning), a non-permit space can quickly become a permit-required space.

Atmospheric Hazards and Testing

Hazardous atmospheres are the leading cause of confined space fatalities. These hazards are often undetectable by human senses. Therefore, rigorous, pre-entry atmospheric testing is mandatory.

The Rule of Three (Testing Sequence)

When testing the atmosphere of a confined space, the tests must be conducted in a strict, specific sequence because the results of one test can affect the reliability of the sensors used in subsequent tests. The mandatory sequence is:

1. Oxygen Content: Test first for oxygen levels.
   • Acceptable range is between 19.5% and 23.5%.
   • Below 19.5% is an oxygen-deficient atmosphere (asphyxiation risk).
   • Above 23.5% is an oxygen-enriched atmosphere (extreme fire/explosion risk).
   • Why first? Combustible gas sensors require sufficient oxygen to operate accurately. If oxygen is low, the LEL reading may be falsely low.
2. Flammable/Combustible Gases (LEL): Test second for flammability.
   • The concentration of flammable gas, vapor, or mist must not exceed 10% of its Lower Explosive Limit (LEL).
   • Why second? An explosion is an immediate, catastrophic threat that must be ruled out before focusing on long-term toxic exposures.
3. Toxic Gases and Vapors: Test third for specific toxic substances.
   • Test for anticipated toxins like Hydrogen Sulfide (H2S) or Carbon Monoxide (CO), ensuring concentrations remain below their respective Permissible Exposure Limits (PELs).

Testing must be done using a calibrated direct-reading instrument. Because gases stratify based on their molecular weight relative to air, testing must evaluate the top, middle, and bottom of the space.

The Permitting Process and Personnel Roles

Entry into a PRCS requires a formal written permit system. The permit is a document that verifies all safety procedures, hazard controls (like LOTO and ventilation), and rescue plans are in place before anyone enters.

The standard defines three critical roles for any PRCS entry:

1. The Authorized Entrant

The entrant is the employee who is authorized by the employer to enter a permit space. They must:

• Know the hazards that may be faced during entry.
• Properly use equipment (e.g., ventilation, lighting, communication, PPE).
• Communicate regularly with the attendant.
• Alert the attendant whenever warning signs of exposure appear or a prohibited condition exists.
• Exit the space immediately if instructed by the attendant, an alarm sounds, or a hazard becomes apparent.

2. The Attendant (Hole Watch)

The attendant is stationed entirely outside the permit space. Their most critical rule is that they must never enter the space to attempt a rescue. Attendants account for more than half of all confined space fatalities because they instinctively rush in to save a collapsed coworker, only to be overcome by the same atmospheric hazard. The attendant must:

• Know the hazards and behavioral effects of exposure.
• Maintain an accurate count of authorized entrants.
• Remain outside the space during entry operations until relieved by another attendant.
• Communicate with entrants to monitor their status.
• Monitor activities inside and outside the space to determine if it is safe for entrants to remain.
• Order an immediate evacuation if a prohibited condition or behavioral effect of hazard exposure is observed.
• Summon rescue and emergency services if needed.

3. The Entry Supervisor

The entry supervisor is the person (often the employer, foreman, or crew chief) responsible for determining if acceptable entry conditions are present. They must:

• Know the hazards of the space.
• Verify that all tests specified by the permit have been conducted.
• Verify that all procedures and equipment (including rescue services) are in place.
• Sign (endorse) the permit to authorize entry.
• Terminate the entry and cancel the permit when work is complete or a prohibited condition arises.