All About Confined Spaces

Maintenance and repair crews across the United States are presented with a dangerous and potentially life threatening situation when they enter a confined space. 

Since a confined space can be encountered in virtually any occupation, it's vital that employers and employees adhere to the standards and regulations outlined by the Occupational Safety and Health Administration (OSHA). 

Stonehouse Signs OSHA Compliant Confined Space Signs

This article takes a look at the definitions of the various types of confined spaces, along with the dangers and hazards they present. 

We also identify the components of a Confined Space Pre-Entry Checklist and/or Permit.

Use These Links to Jump To the Information You Are Interested In:

What is a Confined Space?
Non-Permit vs. Permit Required Confined Space
Dangers and Hazards in Confined Spaces
Entry Permit/Confined Space Pre-Entry Check List
Stonehouse Confined Space Signs and Tags

NOTE: The information presented in this document is intended for general discussion only and should not be used for compliance purposes. For more detailed information on OSHA standards and their application to specific situations, please visit the links provided for the Occupational Health and Safety Administration's website, or contact OSHA directly.

What is a Confined Space?

A confined space has limited or restricted means for entry or exit, and it is not designed for continuous employee occupancy.

Here are some generic examples of confined spaces:

  • Underground vaults
  • Tanks
  • Storage bins
  • Manholes
  • Pits
  • Silos
  • Process vessels
  • Pipelines

OSHA Also offers a comprehensive list of confined space examples grouped by major industry type.

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Non-Permit Confined Space vs. Permit Required Confined Space

There are very specific definitions that help identify whether or not a confined space requires an entry permit and a pre-entry checklist. 

Non-Permit Confined Space

A Non-Permit confined space does not contain or have the potential to contain any hazard capable of causing death or serious physical harm.

Examples of non-permit required confined spaces include:

  • Interiors of HVAC units
  • Certain air plenums and pipe chases
  • Attics
  • Walk-in freezers or refrigerators
  • Some building crawl spaces

Permit Required Confined Space

OSHA uses the term "permit-required confined space" ( or 'permit space') to describe a confined space that:

  • Contains or has a potential to contain a hazardous atmosphere.
  • Contains a material that has the potential for engulfing an entrant.
  • 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.
  • Contains any other recognized serious safety or health hazard, such as unguarded machinery, exposed live wires, or heat stress.

OSHA offers some excellent tools to help identify a confined space for any industry.  For more information, visit their Frequently Asked Questions about Confined Spaces, or utilize the OSHA’s Confined Spaces Advisor, which provides guidance regarding OSHA's Permit-Required Confined Spaces rules for general industry employers.

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Dangers and Hazards in Confined Spaces

Entering a confined space can be extremely dangerous without taking proper precautions.  OSHA has identified several specific hazards that could cause severe injury and death in a confined space.  Every pre-entry checklist and confined space entry permit has to identify any of the following hazards before a worker can enter the space

Hazardous Atmospheres

The most common hazard in a confined space is a hazardous atmosphere. This hazard primarily deals with the air in the confined space and includes oxygen-deficient, oxygen-enriched, flammable, and toxic atmospheres.

Oxygen-Deficient Atmosphere

An oxygen-deficient atmosphere is a confined space that has less than 19.5 percent of available oxygen.  Chemical reactions, sewage or other decomposing organic matter such as domestic waste and plant life can cause the low oxygen level in a confined space.  The work being done in the space or certain chemical reactions can also lower the oxygen level.

In order to have a safe working environment in a confined space, the oxygen level must be between 19.5 and 23.5 percent.  Any level below 19.5 percent is dangerous to a worker's health and safety.

Levels below 10 percent can cause unconsciousness and levels below 8 percent can quickly cause death.

Any confined space with less than 19.5 percent oxygen generally requires an approved self-contained breathing apparatus (SCBA) or supplied air hose with an escape pack.

Oxygen-Enriched Atmosphere

An oxygen-enriched atmosphere is a confined space where the percentage of oxygen is above 23.5 percent.  A high concentration of oxygen will cause flammable materials (such as clothing and hair) to burn violently when ignited. 

Flammable Atmospheres

A flammable atmosphere will only occur when a certain chemical/oxygen mixture is present.  This is usually caused by a build-up of methane or other flammable chemicals that can also occur in confined spaces.

There are two levels that require monitoring in flammable atmospheres- the Lower Flammable Limit (LFL) and the Upper Flammable Limit (UFL).

Flammable gas and vapor will not ignite below the LFL and above the UFL, but between these two levels, a source of ignition (i.e. sparking or electrical tools) could result in an explosion.

Let's take Methane as an example.  Methane is the most common flammable gas in sewers. It is generated by decomposing organic material. The LFL for methane is 5%. When the levels reach 10% of that level, or .5% methane, the space may not be entered.

According to OSHA, a space is unsafe if the flammable gas or vapor level is above 10% of the LFL and workers should not enter.

Toxic Gases and Vapors

Toxic gasses and vapors can come from a wide variety of sources in confined spaces, including:

Products Stored in the Space

  • Gases released when cleaning
  • Materials absorbed into walls
  • Decomposition of materials

Work Performed in the Space

  • Welding, cutting, brazing, soldering
  • Painting, scraping, sanding, degreasing
  • Sealing, bonding, melting

Sewage and other rotting organic materials produce hydrogen sulfide and carbon monoxide, while other toxic substances may have been spilled or dumped into a sewer system.

The atmosphere in a confined space is considered hazardous if toxic chemicals are present that exceed the OSHA Permissible Exposure Limit, which can immediately endanger the workers' lives or health, up to and including death or serious illness.

Other Confined Space Hazards

There are a number of other potential physical and safety hazards inside a confined space, including engulfment, falling objects, temperature extremes, noise, slips, and falls.

  • Engulfment
    Engulfment is the surrounding and effective capture of a person by a liquid or finely divided (flowable) solid substance that can be aspirated to cause death by filling or plugging the respiratory system or can exert enough force on the body to cause death by strangulation, constriction, or crushing. Loose, granular material stored in bins and hoppers (grain, sand, coal, or similar material) can engulf and suffocate a worker. The loose material can also crust or bridge over in a bin and break loose under the weight of a worker.
  • Falling Objects
    Workers in confined spaces should be aware of the possibility of falling objects where work is being done above the worker and in spaces that have topside openings.
  • Temperature Extremes
    Extremely hot or cold temperatures that are caused by work being completed or existing factors (steam cleaning, humidity, extremely cold liquids, etc.)
  • Noise
    Noise within a confined space can be amplified because of the acoustics within the space. Excessive noise can damage hearing and affect communication.
  • Slick/Wet Surfaces
    Slips and falls can occur on wet surfaces causing injury or death to workers. A wet surface will also increase the likelihood and severity of electric shock in areas where electrical circuits, equipment, and tools are used.
  • Any other hazard that could cause serious injury or death.

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Entry Permit/Confined Space Pre-Entry Check List

Confined Space Entry Permits document compliance with section 1910.146(f) of the OSHA Standard for Permit-Required Confined Spaces.  It authorizes entry to a permit-required confined space.  Each entry permit addresses all of the items included below and any additional hazards not addressed in this list that may be present in any particular confined space.

  1. The permit space to be entered
  2. The purpose of the entry
  3. The date and the authorized duration of the entry permit
  4. The authorized entrants within the permit space by name or by such other means (i.e. rosters or tracking systems).
  5. Note: This enables the attendant to determine quickly and accurately which authorized entrants are inside the permit space for the duration of the permit.
  6. The personnel currently serving as attendants by name.
  7. The individual currently serving as entry supervisor by name with a space for the signature or initials of the entry supervisor who originally authorized entry.
  8. The hazards of the permit space.
  9. The measures used to isolate the permit space and to eliminate or control permit space hazards before entry.
    Note: Those measures can include the lockout or tagging of equipment and procedures for purging, inerting, ventilating, and flushing permit spaces.
  10. The acceptable entry conditions.
  11. The results of initial and periodic tests performed, accompanied by the names or initials of the testers and by an indication of when the tests were performed.
  12. The rescue and emergency services that can be summoned and the means (such as the equipment to use and the numbers to call) for summoning those services.
  13. The communication procedures used by authorized entrants and attendants to maintain contact during the entry.
  14. Equipment, such as personal protective equipment, testing equipment, communications equipment, alarm systems, and rescue equipment that is provided to comply with this section.
  15. Any other information whose inclusion is necessary, given the circumstances of the particular confined space, in order to ensure employee safety.
  16. Any additional permits, such as for hot work, that have been issued to authorize work in the permit space.

Appendix D to section 1910.146 presents examples of permits whose elements are considered to comply with the requirements of Permit-required confined spaces. 

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Stonehouse Signs Confined Space Signs and Tags

Stonehouse Signs offers a complete line of confined space signs and tags to identify confined spaces and keep your workers safe while they are performing maintenance and repair.

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Confined Space Signs

OSHA Confined Space Signs- Danger Confined Space Enter By Permit Only OSHA Confined Space Signs- Caution Lifeline Required OSHA Confined Space Signs- Danger Permit Required Confined Space Do Not Enter
OSHA Confined Space Signs- Danger Confined Space Entry Procedures OSHA Confined Space Signs- Danger Confined Space Authorized Personnel Only OSHA Confined Space Signs- Danger Confined Space Hazardous Atmosphere

View our Entire Line of Confined Space Signs Here

Confined Space Tags

OSHA Confined Space Tag- Permit Required Confined Space OSHA Confined Space Tag- Permit Required Confined Space Entry In Progress
OSHA Confined Space Tag- Danger Worker In Confined Space OSHA Confined Space Tag- Danger Do Not Operate Worker in Confined Space

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