Overview of Confined Spaces in Construction (OSHA Subpart AA)

​Confined spaces are a significant safety concern in the construction industry, where hazardous conditions can quickly arise in tight, enclosed areas. OSHA’s Confined Spaces in Construction Standard, also known as Subpart AA, was created to protect workers by establishing requirements for safe entry and work in confined spaces. Let’s explore the basics of Subpart AA, key definitions, specific hazards, and essential safety measures for construction environments.

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What is a Confined Space?

According to OSHA, a confined space is any space that:

1. Is large enough for a worker to enter and perform tasks.
2. Has limited or restricted means for entry or exit.
3. Is not designed for continuous occupancy.

​Common examples of confined spaces in construction include manholes, tanks, crawl spaces, boilers, silos, and underground vaults.

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​Defining Permit-Required Confined Spaces

Subpart AA further identifies “permit-required confined spaces” (PRCS), which are confined spaces with one or more additional hazards. These hazards may include:

• Hazardous atmospheres (such as oxygen deficiency or toxic gases)
• Materials that could engulf an entrant
• Walls that converge inward, or floors that slope downward, which can trap workers
• Other serious health and safety hazards (like electrical or mechanical hazards)

​In cases where a confined space meets these criteria, a written permit program is required, specifying how entry will be controlled, monitored, and supervised.

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​Common Hazards in Confined Spaces

Working in confined spaces poses several risks, many of which can escalate rapidly. Some of the primary hazards include:

1. Oxygen Deficiency or Enrichment: Too little or too much oxygen in the air can be life-threatening. Normal air contains about 21% oxygen. Below 19.5% is considered oxygen-deficient, and above 23.5% is oxygen-enriched, both conditions that can create immediate danger.
   
2. Toxic Gases: Dangerous gases such as hydrogen sulfide, carbon monoxide, and methane can accumulate in confined spaces, posing severe health risks. Toxic gases can result from various activities, including welding, cutting, and cleaning with chemicals.
   
3. Engulfment Hazards: Some spaces contain loose materials like sand, grain, or soil that can engulf a worker, leading to suffocation or crushing injuries.
   
4. Physical Hazards: Uneven surfaces, narrow spaces, poor lighting, and machinery can increase the risk of slips, trips, and falls, as well as contact with moving parts or exposed electrical components.
   
5. Extreme Temperatures: Confined spaces can be prone to extreme temperature changes, leading to heat stress, dehydration, or hypothermia.
   

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​OSHA Requirements Under Subpart AA

To protect workers, OSHA’s Subpart AA standard establishes several requirements for employers:

1. Evaluate the Worksite: Employers must identify and evaluate confined spaces to determine if any are permit-required.
   
2. Develop a Permit System: For permit-required confined spaces, a written entry permit is essential. The permit should document all hazards, required safety measures, and entry and exit procedures.
   
3. Train Workers: Workers involved in confined space entry must receive training to recognize potential hazards and follow safe work practices. This includes authorized entrants, attendants, entry supervisors, and rescue personnel.
   
4. Test the Atmosphere: Before entry, employers must test for oxygen, combustible gases, and toxic air contaminants. Continuous monitoring may be required depending on the work being performed.
   
5. Provide Ventilation and PPE: Adequate ventilation can help control atmospheric hazards. Employers should also provide necessary personal protective equipment (PPE), such as respirators, gloves, and safety harnesses.
   
6. Establish Emergency Procedures: A quick response plan is crucial in confined space work. Employers must ensure that a trained rescue team is available, and that communication systems are in place.
   

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​Roles and Responsibilities in Confined Spaces

OSHA’s standard outlines specific roles to enhance safety in confined spaces:

• Authorized Entrants: Workers authorized to enter the confined space.
• Attendants: Workers stationed outside the space to monitor conditions and assist in emergencies.
• Entry Supervisors: Individuals responsible for authorizing entry, monitoring the conditions, and terminating the entry if necessary.

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​Steps to Safe Confined Space Entry

The process of confined space entry should follow a structured sequence:

1. Identify and Evaluate the confined space hazards.
2. Isolate the space to prevent unauthorized entry.
3. Ventilate the space to control hazardous atmospheres.
4. Monitor air quality before and during entry.
5. Enter and Perform Work under the supervision of trained personnel and with adequate PPE.
6. Terminate the Entry safely by exiting and securing the space once work is complete.

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​Why Compliance with Subpart AA Matters

Non-compliance with Subpart AA can lead to serious injuries, illnesses, or fatalities, as well as substantial OSHA fines. With proper safety measures, training, and awareness, employers can prevent confined space accidents and ensure that their teams return home safely.
For more information on OSHA’s Confined Spaces in Construction standard and in-depth training, you can take our online Confined Space Standards in Construction course. This course is designed to equip you with the knowledge to navigate confined space challenges safely and stay OSHA-compliant.

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OSHA 1926 Subpart AA - Confined Space in Construction Standard

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​OSHA 1926 Subpart AA - Confined Space in Construction Podcast