What you need to know about atmospheric hazards in confined spaces

Atmospheric hazards include things such as oxygen deficiencies, dusts, chemical vapors, welding fumes, fogs, and mists that can interfere with the body’s ability to transport and utilize oxygen, or that have negative toxicological effects on the human body, according to a University of South Carolina paper on confined space training.

Before entry into most confined spaces, a multi-gas meter is commonly used to determine levels of oxygen, carbon monoxide, hydrogen sulfide, and the concentration of combustible gas. Other types of meters and sensors are available to detect concentration of specific gases (chlorine, sulfur dioxide, etc.) if needed.

The most common atmospheric hazards associated with confined spaces are:

  • Oxygen Deficiency
  • Oxygen Displacement
  • Flammable Atmospheres
  • Toxic Gases
  • Oxygen Deficiency

Low levels of oxygen can be caused by the consumption of oxygen during open flame operations such as welding, cutting, or brazing. In addition, low levels of oxygen can be present in manholes that are located near garbage dumps, landfills and oxygen displacement:

Some types of gases will “push” or displace oxygen from a confined space. An example of this is nitrogen. Nitrogen is commonly used to purge some types of tanks. If a person were to enter into the space before the nitrogen was properly removed and vented from the tank, death could result in a matter of minutes.

Flammable Atmospheres:

Three components are necessary for an atmosphere to become flammable: fuel, oxygen, and a source of ignition.

Some confined spaces may contain solvents, fuel oil, gasoline, kerosene, etc. which provide the fuel for combustion. In order for an atmosphere to become flammable, it must have the proper mixture of fuel and oxygen. If the concentration of a specific gas is below the lower explosive limit (LEL) it is too lean to burn. If the concentration is above the upper explosive limit (UEL) it is too rich to burn.

Toxic gases:

Toxic gases can be present in a confined space because the type of manufacturing process uses toxic substances as part of the production process, or biological and chemical “breakdown” of the product being stored in a tank, and from maintenance activities (welding) being performed in the confined space.

Common types of toxic gases encountered in confined spaces are:

  • Hydrogen Sulfide– “sewer gas” a colorless gas with the odor of rotten eggs. Excessive exposure has been linked to many confined space deaths. Hydrogen sulfide causes a loss of our sense of smell, causing people to mistakenly think that the gas has left the space. Hydrogen sulfide inhibits the exchange of oxygen on the cellular level and causes asphyxiation.
  • Carbon monoxide– is an odorless, colorless gas that is formed by burning carbon based fuels (gas, wood). Carbon monoxide inhibits the bodies ability to transport oxygen to all parts of the body.
  • Solvents– many solvents, such as kerosene, gasoline, paint strippers, degreasers, etc. are not only flammable, but if inhaled at high concentrations can cause central nervous system (CNS) effects. CNS effect can include dizziness, drowsiness, lack of concentration, confusion, headaches, coma and death.

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