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Confined/Enclosed Space Hazards

Proper signage indicates the designation of an enclosed or confined space.
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The confined or enclosed spaces on barges may have an atmosphere that is unsafe, causing injury or death. The three main atmospheric hazards while working in a confined or enclosed barge space are:

  1. oxygen deficiency
  2. explosive or flammable atmospheres
  3. atmospheres containing toxic compounds

These hazards might be found in any watertight compartment or other area on a barge with little or no ventilation.

Oxygen-Deficient Atmospheres

Carbon Monoxide Dangers in Confined Spaces
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The most hazardous confined or enclosed space conditions in barge operations occur while exposing workers to oxygen-deficient atmospheres and toxic atmospheres. Toxic vapors may be produced by the previous cargo or cleaning agents and could present significant health hazards. When encountered in confined or enclosed spaces, these agents produce vapors that are often heavier than air. This can cause displacement of air, reducing oxygen levels, which may be fatal. An oxygen-deficient atmosphere inside a tank can be caused by many factors such as:

  • Rusting that may occur in a steel tank where water or water vapor is present. If the tank is airtight, as they are designed to be, then the rusting process would remove oxygen from the tank atmosphere until there is not enough oxygen in the space to support human life.
  • Displacement of oxygen by another gas or vapor, which may occur when a tank is sealed after it is freshly painted. The paint coating may not have time to cure, resulting in the paint vapor displacing oxygen.

Explosive or Flammable Atmospheres

Competent person checks atmosphere prior to entry into a confined space.

An explosive or flammable atmosphere can develop from many sources. Some examples of these sources may include:

  • If you are leasing a barge, a previous user may have dumped waste into the space or used it as a slop tank.
  • A spill of diesel fuel or gasoline on deck may have entered the tank, resulting in an explosive atmosphere.
  • The paint or coating system applied to the tank could ignite if not locally removed prior to hotwork.

Before beginning work in, near or around a confined space or compartment, be sure to do the following:

  1. A visual inspection must first be performed in order to identify potential physical, atmospheric and fire hazards.
  2. The atmosphere must be tested, using a combustible gas meter, not only prior to entry into the space but also if you plan on doing hotwork on a tank exterior. Conducting hotwork on the exterior of a tank can be just as dangerous as when done internally if an explosive atmosphere or a flammable coating is present, which could result in a fire or explosion.
Improper Ventilation Causes Fire in Confined Space
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Identifying Toxic Atmospheres

confined space
Employee entering a confined space.
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Toxic atmospheres are generally the most difficult to identify and can only be determined through testing, which should only be conducted by a qualified person (i.e., marine chemist, competent person, etc.). The potential for a toxic atmosphere is always present and can come from several sources including:

  • A space that is painted and sealed up before the paint has time to cure, causing the off-gassing of the fresh paint to release toxic levels of paint and solvent vapors into the secured space.
  • A tank cover is inadvertently left open that allows nearby engine exhaust to raise the amount of carbon monoxide in the tank to dangerous levels.
  • Contents from a chemical spill (deck above) enters the space.
  • Multiple waste or slop is dumped into a space that creates a toxic compound.

Based on the hazards discussed above, entry into any confined/enclosed space or any space with limited ventilation space on a deck barge should be done with caution.

Accident Summary

Two riggers were capping a sulfur well in a shallow bay, working from the deck of a barge equipped with a crane with a clamshell bucket. The employees dug around the well casing and then set a caisson around the wellhead. Standard procedures required them to cut off the casing and then weld a circular plate over the end. The first employee went into the caisson to wrap a sling around the pipe end, and was asphyxiated due to hydrogen sulfide gas. The second employee entered the caisson to rescue him, and was also overcome by the gas. Neither was wearing respiratory protection (i.e., airline or Self-Contained Breathing Apparatus). Both employees died.

More Information About Atmospheric Hazards and Confined Spaces

OSHA Safety and Health Topics: Confined Spaces

Shipyard Employment e-Tool: Ship Repair

Take OSHAcademy Course 713, Confined Space Safety


Before beginning this quiz, we highly recommend you review the module material. This quiz is designed to allow you to self-check your comprehension of the module content, but only focuses on key concepts and ideas.

Read each question carefully. Select the best answer, even if more than one answer seems possible. When done, click on the "Get Quiz Answers" button. If you do not answer all the questions, you will receive an error message.

Good luck!

1. The most hazardous confined space conditions in barge operations occur while exposing workers to _____.

2. Rusting that may occur within a steel tank where water or water vapor is present may result in which of the following conditions?

3. Which of the following conditions may occur if the paint or coating system applied to a tank was not locally removed prior to hotwork?

4. Which of the following must be completed prior to beginning work in, near or around a confined space?

5. Which of the following are generally the most difficult types of hazardous atmospheres to identify within a barges confined space?

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Important! You will receive an "error" message unless all questions are answered.