Confined Spaces

Safety & Health Manual – Table of Contents

  1. UT Policies on Safety and Health
  2. General Safety
  3. Safety Suggestions and Hazard Reporting
  4. Office Safety
  5. Safety and Health Inspections
  6. Motor Vehicle Safety
  7. Fire/Life Safety
  8. Electrical Safety
  9. Shop Safety
  10. Personal Protective Equipment and Respiratory Protection Program
  11. Confined Spaces


No UTIA Employees are allowed to enter a confined space without advance approval from the Safety Office. If it is determined that a confined space must be entered, the Safety Office must be contacted to provide the necessary training and equipment for the entry.

The following sections provide general guidelines and procedures for confined space entry. This chapter covers the following topics:

  • Confined Space Definitions
  • Atmospheric Issues
  • Trenching/Shoring

Confined Space Definitions

Confined Space – any enclosed area with the following characteristics:

  • limited means of entry or exit – AND –
  • structure that is not designed for extended human occupation – AND –
  • potential for engulfment, entrapment, etc. – OR –
  • atmosphere that is actually or potentially hazardous.

Examples of confined spaces include the following: Crawl spaces, Manholes, Silos, Tanks, Trenches, Tunnels.

Note: Because confined spaces offer limited means of entry or exit and may contain hazards, employees must comply with 29 CFR 1910.146 and the UTIA Confined Space Entry Program when working in these areas. The Confined Space Entry Program is available from the Safety Office. If you have any questions about confined spaces, contact the Safety Office.

Permit-Required Confined Space – Confined space that contains actually or potentially hazardous atmosphere or the potential for engulfment or entrapment by particulate matter, equipment, or liquid.

Entry – Physical act of entering a confined space. An entry occurs when any part of a worker’s body breaks the plane of the confined space opening.

Authorized Entrants – Properly trained workers with the authorization to enter confined spaces.

Authorized Attendant – Properly trained worker who is positioned outside a confined space. This person monitors the entrants within a confined space and the external surroundings.

Person Authorizing Entry – Worker who is properly trained in administrative, technical, and managerial aspects of confined space entry. This person authorizes entry and has the authority to terminate entry when conditions become unfavorable.

Hazardous Atmosphere – Atmosphere that is oxygen enriched, oxygen deficient, combustible, toxic, or otherwise immediately dangerous to life or health.

Hotwork – Operations that could provide a source of ignition, such as riveting, welding, cutting, burning, or heating.​

Monitoring the Atmosphere

Due to poor ventilation and physical structure, the atmosphere in confined spaces may be actually or potentially hazardous. Atmospheric hazards include the following:

  • oxygen deficient or oxygen enriched atmospheres
  • combustible atmospheres
  • toxic atmospheres
  • any other atmosphere that is immediately dangerous to life or health

Employees trained in atmospheric monitoring will test several points in a confined space for the following:

  • oxygen content
  • combustible atmosphere
  • potential toxic contaminants

Atmospheric Issues

Oxygen enriched atmospheres are more than 23.5 percent oxygen; oxygen deficient atmospheres are less than 19.5 percent oxygen. Certain chemical or biological reactions may reduce oxygen over time, but employee operations such as cutting or welding may reduce oxygen content very quickly. Oxygen levels must be tested regularly whenever hotwork is performed within a confined space.

The following graph outlines human reaction to various oxygen levels:

Human Reaction to Oxygen Concentrations  

  • 23.5% – Oxygen Enriched 
  • 21.0% – Normal Atmosphere 
  • 21.0% – Normal Atmosphere 
  • 19.5% – Minimum for Safe Entry 
  • 16.0% – Impaired Judgement & Breathing 
  • 14.0% – Faulty Judgement & Rapid Fatigue 
  • 6.0% – Difficult Breathing & Death in Minutes

Combustible Atmospheres Combustible atmospheres have enough oxygen and flammable vapor, gas, or dust to ignite and support a fire or explosion if exposed to flames, sparks, or heat. Oxygen-enriched atmospheres and hazardous atmospheres in excess of their lower flammable limits are extremely combustible and dangerous.

Toxic Atmospheres Toxic atmospheres can cause injury, illness, or death. Safety concerns include inhalation and skin exposure. If the identity of the toxic atmosphere is known, check all appropriate Material Safety Data Sheets (MSDSs) for threshold limit values and recommended personal protective equipment. If the identity of the toxic atmosphere is not known, use maximum PPE (i.e. Self Contained Breathing Apparatus).


Ventilation controls the atmospheric hazards of a confined space by replacing unsafe air with clean, breathable air. There are several methods for ventilating a confined space. The method and equipment used depend on the following factors:

  • size of the confined space
  • atmosphere
  • source of the makeup air

IMPORTANT: Ventilation alone cannot reduce some atmospheric hazards to safe levels. Use atmospheric testing to confirm whether the ventilation system has been successful.

Trenching and Shoring

Some operations such as trenching result in confined spaces. Shoring or sloping systems are necessary to protect these spaces and reduce the chance for cave-ins.

A trench is a narrow excavation below the ground. Trenches are typically deeper than they are wide; however, the width of a trench is less than 15 feet. Trenches may become confined spaces when an employee must enter the area to work, and the conditions in section 21.2 exist.

A shoring system consists of a structure that supports the sides of an excavation and is designed to prevent cave-ins. Employees must follow all the requirements associated with confined spaces when working within trenches. Prior to any trenching activities, you must contact the Safety Office.