Silent, Invisible, Insidious & Deadly...

By Pat Furr, Safety Officer & VPP Coordinator for Roco Rescue, Inc.

Oxygen-Depleted Atmospheric Hazards in Confined Spaces

It will take your breath away! This is a phrase often used to describe tremendous beauty, or exhilaration. However, in an oxygen-depleted environment, this phrase has a much more ominous meaning. The emotion it elicits is hardly pleasant and joyful. Confusion, panic, impending doom, and okay... maybe even euphoria, which has been reported in near drowning cases, but the euphoria is a late onset emotion once the brain is deprived of oxygen. Suffice to say, having your breath taken away in an oxygen-depleted environment is never a good thing!

In my prior career with USAF Pararescue, I underwent regularly scheduled physiological training in an altitude chamber; otherwise, known as a hypobaric chamber. This was used to train me to recognize the onset of hypoxia (low physiologic oxygen content) and the symptoms that are particular to me. The symptoms of hypoxia differ from person to person and mine were pretty subtle. A loss of peripheral vision and color acuity, a slight warming of the sides of my neck and face, but other than those symptoms, I didn’t have any dramatic, obvious clues that I was in trouble. On at least two occasions, I had to be told by the chamber operator to don my oxygen mask. Once I did, the return to normalcy was profound! I was then able to jot down my symptoms as I remembered them. As I was undergoing my slide into hypoxia, I was given basic written tests to perform such as simple addition problems, connecting the dots, finishing incomplete squares and circles. In every case, I thought that I was doing really well on my assignment; that is until my oxygen mask was returned and I reviewed my work. FAIL!!! This exercise was intended to demonstrate to me the insidious nature of hypoxia and the unrecognized affects it has on coordination and judgment.

My experiences in the altitude chamber were educational and potentially lifesaving if I were ever exposed to a low oxygen environment. By having experienced my subtle symptoms multiple times, perhaps I would recognize them in a lower than normal oxygen environment and be able to take action to rescue myself. However, the environment that I was exposed to was probably in the range of 12% oxygen by volume give or take. In lower concentrations, say below 10%, the onset of impaired judgment would be so rapid that I would have little chance to recognize and react on my own behalf. In extremely low concentrations of 0-8%, there is little chance for anyone to take self-rescue actions. More than likely, the individual will pass out after only one or two gasping breaths. And, most importantly, my experiences were in a controlled environment with highly trained observers and emergency personnel standing by. This is not always the case during confined space entry operations.

How do we end up with depleted oxygen concentrations in confined spaces? 

There are several ways, but I am going to address two broad categories of occurrence: (a) planned, and (b) unplanned. Planned low oxygen concentrations may be unavoidable when doing entries that require an inert gas environment, such as certain types of welding or when doing work in a flammable or explosive atmosphere. By removing the oxygen, one of the three elements of flame is eliminated. There will remain fuel and possibly a source of ignition, but by removing the oxygen, there is no potential for fire in nearly every instance. Even during planned oxygen depleted operations, things have a potential to go wrong. Equipment failure is one possible cause. Faulty supplied air breathing systems can be the culprit. It may be as simple as a failed “O” ring, a faulty diverter valve, a lost connection on an airline respirator system, and many other links of equipment. Or, it could be human error – such as not tending airlines and causing the mask to be dislodged or pulled completely off; failure to change out bottles on the SAR cart; exceeding the safe time and egress requirements if using backpack SCBA; or again, any number of human failures. So you can see that even during planned low O2 entries, the potential for an incident is quite high. That is why OSHA 1910.134 has such stringent requirements for entry into an atmospheric IDLH environment.

It is the unplanned depleted oxygen environments that seem to cause the most incidents, however. Within unplanned low O2 entries, I would like to further categorize them into two separate areas.

1. Unplanned...in that the atmospheric hazard was thought to be controlled, but the potential for the hazard to appear was realized, and indeed created the low oxygen hazard. This could be due to improper isolation techniques or equipment failure.
2. Unplanned and unanticipated...this is the one that really seems to be causing problems. It may happen in permit-required confined spaces and also in non-permit required confined spaces. Upon evaluation, the entry team may have identified the space as non-permit required and assumed there was no need to perform pre-entry atmospheric monitoring. In several incidents, unbeknownst to the entry team, a prior entry team introduced an inert gas into the space for their particular work activities and failed in two ways. The team did not ventilate the space to remove the inert gas and test it afterwards; and, more importantly, the prior entry team failed to communicate the presence of the inert gas to any potential follow-on entrants. Or it may be that the information regarding the inert gas was communicated, but that information was lost in the shuffle. It may have never made it to the follow-on entry team – or that team may have failed to properly process the information. As you can imagine, this type situation has not only led to the demise of the unaware follow-on entrant, but also to several would-be rescuers that attempted rescue without any clue that the oxygen concentration was at a lethal level.

So what is the solution? 

Although this simple step will not “guarantee” a safe entry operation, I know for a fact that by simply employing an atmospheric monitor to test for oxygen will save many lives. And, don’t limit the use of atmospheric monitors for entries into known or potentially low O2 atmospheres! That is an OSHA minimum, so why not exceed that minimum requirement and get into the habit of testing the oxygen concentration for ALL entries? And, not just for permit-required spaces, include non-permit spaces as well. You just never know. Also when monitoring, don’t forget to test the various levels of the space and all breathing zones. Various gases tend to stratify, some being heavier than air, and some lighter, while others are nearly equal and will diffuse universally. Maintain your monitors, calibrate them and bump test them as required by the manufacturer and use them regularly. They are easy to use and relatively inexpensive. They have saved many lives and will continue to do so, if used properly.

Be safe out there and monitor, monitor, monitor!

Although this article has focused on low oxygen atmospheres, we do not mean to minimize the potential for other hazardous atmospheres, such as toxic or flammable. It is just our experience that of all the hazardous atmospheres, it seems that low oxygen is the one that crops up more often and continues to claim a disproportionate number of entrants AND would-be rescuers.