Confined Space Stratification

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The Safety Print - Safety Rise

Confined Space Stratification

All confined spaces have the potential for developing a hazardous atmosphere. As part of the overall confined space hazard evaluation, trained personnel must reasonably expect that a confined space will have atmosphere concerns. Some gases layer in confined spaces. Some gather at the top of the space, while others gather in the middle or floor. This is called stratification. Remember stratification when doing atmosphere testing - the life-saving component of confined space entry procedures.

STRATIFICATION – LAYERING OF GASES IN A SPACE

1. GASES AT THE TOP
• Natural Gas
• Methane
• Also remember that HEAT can take contaminants to the top as well.
2. GASES IN THE MIDDLE
• Carbon monoxide
• Mixtures of gases in the top and bottom of the space
3. GASES AT THE BOTTOM
• Propane
• Chlorine
• Gasoline
• Hydrogen Sulfide

Remember that cold air can cause toxic contaminants to stay at floor level. 

• Cooler air sinks

Test just outside of the enternce also for Good, Poor , Deadly Airs

• Always test the air at various levels to be sure that the entire space is safe.
• Good air near the opening doesnot means there is good air at the bottom 

Remember:

• Check Often: Oxygen, Flammables, Toxics.
• Check for oxygen contects: At least 19.5% and less than 23.5%.
• Check for flammable: Less than 10% of the LEL.
• Check for toxic gasses: Most commonly carbon monoxide (PEL <35 ppm) or any other hazardous materials as determined by the use of the space.

NOTICE! Any time a limit is exceeded, no matter what the reason, all personnel shall immediately exit the space, and no others shall enter until atmospheric conditions are returned to safe levels.