Air Quality in Confined Space


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Air Quality in a Confined Space

Working in a confined space brings a set of challenges and hazards far different than any other type of work. The Occupational Safety and Health Administration defines a confined space as any space that “has limited or restricted means of entry or exit, is large enough for an employee to enter and perform assigned work and is not designed for continuous occupancy by the employee.”1 Examples of confined spaces include:

  • Underground vaults,
  • Silos
  • Tanks,
  • Storage bins,
  • Pits, and
  • Vessels.

One of the major concerns when working in a confined space is air quality and the lack of natural ventilation. Preparing for this hazard can make a significant difference in the outcome of the project.

Air Quality and Ventilation in a Confined Space

Air quality in a confined space can quickly be compromised. Natural ventilation is not usually sufficient to maintain breathable air quality at lower elevations with limited air circulation. In addition, conditions in the confined space can change as work is performed. Performing hot work such as welding, flame cutting, or grinding can release particles into the air or decrease oxygen supply. The substances brought into the space for the work could also affect air quality.

It is also important to remember air quality can vary greatly across the space depending on elevation. This is called stratification – the layering of different air compositions from floor to ceiling. If we think back to high school Chemistry class, we’ll remember that substances will settle depending on their density. Just as oil will sink to the bottom when mixed with water, some chemical substances are lighter or heavier than air and will settle accordingly. Once in the space, use air monitors frequently to check for stratification, however, take some time to plan before entering. For any substance or material that you plan to use, check the Safety Data Sheets for information on density. If the densities across substances vary greatly, you can anticipate and prepare for stratification.

In many cases, the scope of work will change during the job. For example, you enter a tank to inspect/repair a suspected steam coil leak. After identifying the leak near the entrance of the vessel, you repair and test again, only to identify another leak above you. The air quality at that elevation might be different due to the density of substances within the space. Be aware of the possibility for differing air qualities and prepare to adapt to complete the job.

Once you know the air quality aspects of the space, you can properly ventilate to increase air quality. The ventilation system, fans and hoses, can be set up to ensure good air quality throughout the space and maintained at that level during the course of the entry. Below is an example of a ventilation system used for a confined space entry job.

Related Articles:

Permit-Required Confined Spaces

How To Protect Employees From Confined Spaces Hazards

For specific questions regarding Permit Required Confined Spaces, air quality and ventilation systems, contact our Safety Helpline and speak with a Safety Professional today.


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