Confined Spaces: Hazards, Risks, and Safety Measures

Posted on Mar 31, 2025 in Chemistry

Confined Spaces: Definition and Examples

A confined space is any space with limited openings for entry and exit, where an employee can fully enter. These spaces often have unfavorable natural ventilation, allowing pollutants to accumulate, creating toxic, flammable, or oxygen-deficient atmospheres. Confined spaces are not designed for continuous human occupancy.

NIOSH Definition of Confined Space

The National Institute for Occupational Safety and Health (NIOSH) defines a confined space as any space with limited openings for entry and exit, unfavorable natural ventilation, potential for pollutant accumulation (toxic or flammable), and/or an oxygen-deficient atmosphere. These spaces are not intended for continuous worker occupancy.

Examples of Confined Spaces

Examples of confined spaces include, but are not limited to:

  • Ponds
  • Wells
  • Sewers
  • Basements
  • Tanks
  • Boilers
  • Reactors
  • Bodegas
  • Double bottom vessels
  • Silos
  • Tunnels
  • Cable ducts
  • Air conditioning ducts
  • Sewage lift shafts
  • Industrial smokestacks
  • Conveyor tunnels
  • Distillation towers
  • Trenches

Confined Space Risks

General Risks

General risks associated with confined spaces include:

  • Entrapment
  • Falls
  • Physiological disorders due to heat, cold, noise, and vibration
  • Awkward postures
  • Impact injuries
  • Thermal burns

Specific Risks

Specific risks associated with confined spaces include:

  1. Explosion and Fire: Primarily due to the presence of flammable or combustible gases, chemical reactions, solvents, or explosive particulate atmospheres with excess oxygen.
  2. Choking: Caused by non-toxic gases like nitrogen, carbon monoxide, argon, and helium displacing oxygen.
  3. Poisoning: Due to toxic gases, liquids, or solid fumes that can cause poisoning and death.
  4. Burns: Resulting from contact with toxic gases or liquids, causing thermal or chemical burns to the skin.

Confined Space Prevention Measures

General prevention measures in confined spaces include:

  • Training workers specifically for confined space work.
  • Following established procedures and instructions.
  • Obtaining a safe work permit before entry.
  • Checking the atmosphere before and during work.
  • Ensuring adequate ventilation.
  • Monitoring working conditions continuously.
  • Having a rescue system in place.
  • Maintaining positive pressure or continuous flow extraction with a forced extraction system.
  • Supplying air from an external source.
  • Securing safe access to the confined space.

Contaminated Atmospheres

Atmospheric Hazards

Atmospheric hazards in confined spaces include:

  1. Oxygen-deficient atmospheres: Less than 19.5% oxygen.
  2. Oxygen-enriched atmospheres: Greater than 23.5% oxygen.
  3. Explosive atmospheres: Exceeding 10% of the lower explosive limit (LEL).
  4. Toxic atmospheres: Concentrations of toxic substances exceeding OSHA permissible exposure limits (PELs).
  5. Asphyxiating atmospheres: Dust and haze reducing visibility to less than 1.5 meters.

Oxygen Deficiency

Oxygen deficiency is defined as an atmosphere containing less than 19.5% oxygen. Work in these conditions requires self-contained breathing apparatus or supplied-air respirators.

Causes of Oxygen Deficiency

  • Displacement: By gases like argon, helium, and neon.
  • Consumption: Through oxidation, corrosion, fermentation, or oxygen-consuming work involving flames or fire.

Excess Oxygen

An oxygen concentration exceeding 23.5% is considered an oxygen-enriched atmosphere, increasing the risk of fire or explosion. At 28% concentration, flame-resistant textiles and clothing lose their protective properties. Increased oxygen levels in the air and fuel sources can easily ignite.