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Appendix C. Ventilation Of Confined Spaces

Ventilation is one of the most effective means of controlling hazardous atmospheres in confined spaces. In this procedure, clean air replaces contaminated air by natural or forced (mechanical) ventilation.

When ventilating a confined space, the following factors must by taken into consideration:

Volume of air: This determines the capacity of the blower or ejector.

Type of atmosphere: This will determine the type of blower or ejector used and the length of time needed to ventilate until it is safe for people to enter the space.

Access to space: This determines how to get the ventilating air into and out of the space.

Power requirements and availability: This will influence the power source and fan motor size. A portable generator may be required as a source of power.

Cost, efficiency and maintenance: This may have an effect on the type of device that is selected and what is necessary to keep it working properly.

Shape of space: This will affect the typed of directional device needed and the amount of air pressure required to provide sufficient ventilation.

Source of clean air: This is necessary to ensure adequate ventilation.

Length of time ventilation is needed: This is determined by the type of contaminant and the work that is to be done in the space

Type of work to be done: This determines whether local exhaust ventilation or general ventilation is required.

Ventilation Guide

  1. Select fan with a capacity to quickly replace the air in the space. Limitations are pasted on the fan housing
  2. Use reliable, grounded electrical power.
  3. Eliminate any hazardous atmosphere. Exhaust toxic and flammable air; supply fresh air when oxygen-deficient.
  4. Provide constant circulation of fresh air while space is occupied.
    • Natural ventilation is allowable only on "non-permit" entry.
    • Direct high-velocity supply ventilation to mix the air throughout the space.
    • Capture contaminants during hot work or cleaning with solvents by using additional local (or point) exhaust.
    • Pure oxygen is not "fresh air". Never use bottled oxygen for ventilation.
  5. Arrange ductwork to ensure safety:
    • Locate supply fan intake away from flammable or toxic air.
    • Position exhaust fan outlet to avoid recirculation of bad air or endangering others outside the space.
    • Position exhaust duct inlet next to the source of contaminants.
    • Keep ducts short and straight.
    • Make sure air circulates through entire space and does not short-circuit.
  6. Monitor the air to ensure ventilation is keeping the air safe to breathe.

Confined Space Table of Contents


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