Page 15 - Confined Space Training - Student Manual 2021

The atmosphere of a permit space which may contain a hazardous atmosphere should be tested
for residue of all contaminants identified by evaluation testing using permit specified equipment
to determine that residual concentrations at the time of testing and entry are within the range of
acceptable entry conditions.

Results of testing (i.e., actual concentration, etc.) must be recorded on the permit in the space
provided adjacent to the stipulated acceptable entry condition.

Monitoring Protocol
Testing Locations
When monitoring for entries involving a descent into a potential hazardous atmosphere, the
atmosphere should be tested at approximately 4 feet (1.22 m) in the direction of travel and to
each side of the space.

Remember that instrument sensors require time to clear and respond to new concentrations if
they differ from previous responses. Testing that does not permit a meter’s sensors to adjust to
new concentrations will produce false readings. It is best to test for 1 to 2 minutes at each location.
If the meter is equipped with a tubing extension, the meter will require additional time to clear the
tubing before new atmosphere can reach the sensor.

Be especially alert for dead ends or areas of low air movement where concentrations of unwanted
materials could have developed.

Testing Sequence
1. A test for oxygen is performed first because most combustible has meters are oxygen
dependent and will not provide reliable readings in an oxygen deficient atmosphere.
2. Combustible gases are tested for second because the threat of fire and explosion are
both more immediate and more life threatening, in most cases, than exposure to toxic
gases and vapors.
3. Testing for toxic gases and vapors is performed last.

All atmospheric tests are important and test results must be recorded on the entry permit.
NOTE: Not believing the instrument readings is one of the biggest mistakes you can
make. If you question instrument readings, obtain a second instrument to verify the
atmosphere is safe for entry.

Oxygen (O2) Concentrations
Asphyxiation, or suffocation, accounts for 47% of all confined space deaths. The air we breathe
is a mixture of gases that includes oxygen. Normal air contains 20.9% oxygen by volume.
Deviations from this level, either higher or lower, are a major concern in confined spaces.

The lower and upper limits for oxygen in a permit-required confined space are 19.5% - 23.5%.
Oxygen deficiency is a common problem in confined space. Oxygen levels below 19.5% by
volume are considered unsafe and can result from either the consumption or displacement of
ambient oxygen. Oxygen concentration reduction can be caused by:
• Oxidation of metals (rusting)
• Combustion (welding and cutting torches)
• Decomposition of organic matter (rotting foods, plant life and fermentation)

Confined Space Training for Entrants, Attendants & Supervisors 15