Working in a confined space can expose workers to serious hazards that aren’t always obvious from the outside.
Tanks, silos, manholes, pipelines, sewers, pits, and underground chambers may have limited entry and exit points, poor ventilation, or hazardous atmospheres.
Understanding confined space hazards and precautions is essential for preventing injuries, toxic exposure, fires, and fatalities.
Before anyone enters a confined space, the hazards should be identified, evaluated, and controlled through a proper safety program.
What Is a Confined Space?
A confined space is generally an area large enough for a worker to enter and perform work, has limited or restricted means of entry or exit, and isn’t designed for continuous occupancy.
Common examples include storage tanks, boilers, sewers, silos, tunnels, crawl spaces, pits, vessels, and utility vaults.
Some confined spaces are considered permit-required confined spaces because they contain, or have the potential to contain, serious hazards such as toxic gases, oxygen deficiency, engulfment hazards, or conditions that could trap or incapacitate a worker.
Common Confined Space Hazards
1. Oxygen Deficiency
One of the most serious confined space hazards is an atmosphere with insufficient oxygen. Oxygen can be displaced by other gases or consumed through processes such as combustion, corrosion, or decomposition.
Workers may experience dizziness, confusion, unconsciousness, or death when oxygen levels become dangerously low.
Precaution: Test the atmosphere before entry and continue monitoring as required. Never rely on smell or other senses to determine whether an atmosphere is safe.
2. Toxic Gases and Vapors
Confined spaces can accumulate hazardous gases and vapors. Examples include hydrogen sulfide, carbon monoxide, and other chemical vapors.
Some gases can be toxic at relatively low concentrations, while others can quickly overwhelm a worker.
Precaution: Conduct atmospheric testing using properly calibrated equipment. Provide appropriate ventilation and respiratory protection when required by the hazard assessment.
3. Flammable or Explosive Atmospheres
Flammable gases, vapors, or combustible dust can accumulate inside confined spaces. A spark, flame, hot surface, or electrical equipment can potentially ignite the atmosphere.
Precaution: Test for flammable atmospheres before and during work when conditions can change. Eliminate ignition sources and use equipment appropriate for the environment.
4. Engulfment
Workers can become buried or trapped by materials such as grain, sand, soil, sludge, or other bulk materials. Engulfment can occur quickly and may prevent a worker from escaping or breathing.
Precaution: Isolate material flow before entry and implement procedures that prevent unexpected movement of materials into the space.
5. Mechanical and Electrical Hazards
Moving equipment, rotating machinery, electrical systems, valves, conveyors, and other energy sources can create serious hazards inside confined spaces.
Precaution: Lockout/tagout applicable energy sources before entry. Verify that equipment has been properly isolated and cannot unexpectedly start or release stored energy.
6. Poor Ventilation
Limited airflow can allow toxic gases, vapors, or heat to accumulate. Poor ventilation can also contribute to oxygen deficiency.
Precaution: Use mechanical ventilation when appropriate and continuously evaluate the atmosphere. Ventilation should never be treated as a substitute for atmospheric testing.
7. Heat Stress
Confined spaces can become extremely hot, particularly tanks, boilers, underground spaces, and areas exposed to hot equipment or weather.
Precaution: Control the heat source where possible, provide adequate ventilation, schedule appropriate work and rest periods, and ensure workers have access to drinking water.
8. Falls and Physical Hazards
Ladders, slippery surfaces, uneven floors, narrow openings, and elevated work areas can create fall and access hazards.
Precaution: Provide safe entry and exit systems, inspect ladders and access equipment, control slip and trip hazards, and use appropriate fall protection where required.
9. Limited Visibility
Poor lighting can make it difficult to identify hazards, operate equipment, or find an exit during an emergency.
Precaution: Provide suitable lighting and keep access routes clear. Emergency lighting may also be necessary depending on the work environment.
10. Biological Hazards
Sewers, wastewater systems, agricultural facilities, and other confined spaces may contain bacteria, viruses, mold, insects, rodents, or other biological hazards.
Precaution: Identify potential biological exposures and provide appropriate hygiene practices, PPE, vaccinations where applicable, and other controls based on the hazard assessment.
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Confined Space Precautions
Effective confined space safety starts before anyone enters. A competent person or qualified safety professional should evaluate the space and determine which hazards are present or could develop during the work.
Conduct a Hazard Assessment
Identify atmospheric, mechanical, electrical, physical, chemical, biological, and environmental hazards. Consider how the work itself could introduce additional hazards.
Conditions can change after entry, so the assessment should account for hazards that may develop during the job.
Test the Atmosphere
Atmospheric testing is one of the most important confined space precautions. Depending on the hazards, testing may include oxygen concentration, flammable gases and vapors, and toxic contaminants.
Testing should be performed with properly maintained and calibrated instruments by personnel who understand how to use them.
Provide Ventilation
Adequate ventilation can help control hazardous atmospheres and heat. However, ventilation requirements depend on the specific space and contaminants involved.
Workers should continue atmospheric monitoring even when ventilation is being used.
Isolate Energy Sources
Before entry, identify and isolate hazardous energy sources. This can include electrical, hydraulic, pneumatic, mechanical, chemical, thermal, and other forms of energy.
Lockout/tagout procedures should be followed where applicable, and isolation should be verified before workers enter.
Use Appropriate Personal Protective Equipment
PPE should be selected based on the hazards identified during the assessment. Depending on the work, this may include a hard hat, safety glasses, gloves, protective clothing, hearing protection, safety footwear, respiratory protection, or fall protection equipment.
PPE should complement, rather than replace, effective engineering and administrative controls.
Establish Communication
Workers inside a confined space need a reliable way to communicate with the attendant or other personnel outside the space.
Communication systems should be tested before work begins, particularly when workers cannot be seen or heard directly.
Have an Emergency Rescue Plan
A rescue plan should be developed before entry, not after an emergency occurs. The plan should identify rescue equipment, personnel, communication methods, and procedures for contacting emergency services.
Simply having a phone number available isn’t a complete rescue plan.
The Importance of a Confined Space Attendant
For permit-required confined space operations, an attendant can play a critical role in worker safety. The attendant remains outside the space, monitors authorized entrants, maintains communication, and initiates appropriate emergency procedures when necessary.
An attendant should understand the hazards of the space and know when an evacuation is required. The attendant should not enter the confined space to perform an unplanned rescue unless properly trained, equipped, and authorized to do so.
Confined Space Entry Checklist
Before entering a confined space, verify that:
- The space has been properly identified and evaluated.
- Hazards have been assessed and controlled.
- Atmospheric testing has been completed as required.
- Ventilation is adequate when needed.
- Hazardous energy has been isolated.
- Required PPE is available and properly fitted.
- Safe entry and exit methods are in place.
- Communication systems are working.
- Required permits and procedures have been completed.
- An emergency rescue plan is in place.
- Workers understand the hazards and entry procedures.
Final Thoughts
Confined space hazards can be difficult to recognize and can change quickly. Oxygen deficiency, toxic gases, fire, engulfment, mechanical hazards, falls, heat, and poor ventilation are among the most important risks to address.
The safest approach is to identify hazards before entry, eliminate or control them where possible, test the atmosphere, provide appropriate equipment and training, maintain communication, and have a realistic rescue plan in place.
For workplaces in the United States, confined space procedures should be developed around the applicable OSHA requirements and the specific hazards of the workplace. Always follow applicable regulations, manufacturer instructions, and your organization’s established safety procedures.
Frequently Asked Questions
1. What are the most common confined space hazards?
Common hazards include oxygen deficiency, toxic gases, flammable atmospheres, engulfment, electrical and mechanical hazards, falls, heat stress, and poor ventilation.
2. How do you know if a confined space is safe to enter?
The space should be properly assessed and, when required, tested for oxygen, toxic gases, and flammable vapors before entry. Conditions should also be monitored as necessary during the work.
3. What PPE is needed for confined space entry?
PPE depends on the hazards but may include a hard hat, safety glasses, gloves, protective clothing, safety footwear, respiratory protection, and fall protection equipment.
4. Why is atmospheric testing important?
Atmospheric testing helps identify dangerous conditions such as low oxygen, toxic gases, or flammable vapors that may not be visible or detectable by smell.
5. Is a rescue plan required for confined space work?
A suitable emergency and rescue plan should be established before entry when the hazards and applicable regulations require it. Workers should never rely on improvised rescue procedures during an emergency.