Confined Space Hazard – Oxygen Deficiency

October 1, 2012 Dave Weber No Comments



There are a variety of hazards that could exist inside of a confined space – oxygen deficiency is one of them.  Oxygen can be depleted before entry is made due to:

  • the rusting process of metal that is within the space
  • the decomposition of material that is within the confined space
  • oxygen being displaced by other gases 

It is important to use a properly calibrated multi-gas tester to measure the oxygen levels before entry is made.  Test the oxygen levels at various different areas and heights within the confined space.  This can be facilitated through the use of an extension wand on your multi-gas tester.

If the measured oxygen levels are below the safe level, I will usually postpone the entry until the oxygen levels become safe.  Entering a confined space that is known to be oxygen deficient (even with an air supplied respirator) is extremely dangerous and should only be done by highly trained and qualified professionals.

I ventilate a confined space with a fan blowing into the space for at least one-hour before any entry is made.  Every few minutes I like to reposition the fan to better ventilate the entire space.

Even if oxygen levels are safe at the beginning of the entry,  please remember that oxygen can be depleted during the entry if welding is performed (or any other process that uses up oxygen).  Have the entrant wear the multi-gas tester during their entire entry.  Most multi-gas testers have an alarm that will sound should the oxygen levels drop below the safe level.  If the alarm sounds, the confined space must be vacated immediately.

During the entire entry, be sure to leave the ventilating fan(s) running.  The fan should be fairly quiet;  it must not interfere with the attendant(s)’ verbal communications with the entrant(s). 

If the ventilating fan is run by electricity, and the area where it is being used is (or could become) wet or damp, minimize the electrical hazard by protecting  the fan with a GFCI.


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