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Confined Space Metering: Concentration Kills

July 9, 2013
Breathe easier in confined spaces with a properly charged, calibrated and maintained meter.

I was providing confined space entry rescue for a welding crew when the meter's alarm started flashing. The plant, a gas-separation facility, provided mostly oxygen to the steel mill next door and bottled a variety of other gases for local industry and hospitals. The largest byproduct of this operation is nitrogen.

"Those welders are always messing with that meter," the site safety manager told me as I pulled the tubing out of the opening of the separating tank. The crew was TIG welding the piping inside a tank where the crew had made entry through an opening in the top while we observed from a fully extended scissor lift. 

The site safety manager was suggesting that the welder had put his finger over the end of the tube as a joke to make the meter alarm. The meter senses low airflow and alarms just as it would if it had triggered one of its five sensors. 

I pulled the tubing out of the hole, and the welder must have noticed, because he came following after it like a fish on my line. He poked his torso out of the hole and threw out his hands, palms to the sky, in the universal sign for "What the heck!?" I laughed at him as I thought he was really carrying this joke to the fullest. Coming out of the hole to act concerned about the meter alarming, when he was the one who set it off!

I reset the meter and lowered the tubing back in the hole. This four-gas meter measured the standard gases: oxygen, hydrogen sulfide, carbon monoxide and lower-explosive limit based on methane. Once it was lowered, I busied myself with securing it to the lift and checking the rigging. 

But after about a minute, the meter began to alarm again. I thought, "What is the deal with this knucklehead? Is he really messing with the tubing again?" 

I turned to the site safety guy to ask if he could make this stop only to find him lying on the deck of the scissor lift, looking alive but awfully confused. I checked the welder and he was fine, so I lowered the lift to off load the site safety manager. He was standing and coherent before the lift got to the ground. 

What the heck just happened?

Concentration Kills

What happened to that site safety manager was, quite simply, science. 

The plant separated gases through a variety of refinement processes involving pressure differentials and filtering through a dry medium. Nitrogen is the main byproduct of that process, as it is the major component of the air we breathe. 

Nitrogen is an inert gas. Typically, it's innocuous filler, which has an inverse relationship to oxygen concentrations. Oxygen and nitrogen are the two largest components of the air we breathe. When the concentration of nitrogen in the air increases, it has the ability to force out the available oxygen. Simply stated, too much nitrogen can lead to a worker to lose consciousness or worse due to asphyxiation. At that same plant, a worker had become semi-conscious while walking at ground level into a nitrogen cloud. He was wearing a meter. It was audibly alarming when they found him on the deck.

In this facility, the leftover nitrogen is dumped out of large stacks over 80 feet in the air. Normally, they are so high above the action that even in the worst atmospheric conditions, they do not pose a risk. On the day of this incident, however, we were working just a few feet below the output of the nitrogen dump stack and almost directly downwind of the distal opening. The atmospheric conditions changed from high pressure, windy and sunny to low pressure, moist and cloudy. As a result, the nitrogen that had been blowing over our heads all day now was dropping out of the stack and lingering around our confined space entry work site. It had changed the oxygen concentration inside the tank and out, put our meter into alarm and landed the site safety manager on his behind. The wind must have been just right to push the cone of nitrogen past me, so I remained unaffected.

Low pressure also causes problems in my other line of work as a city firefighter. For example, on high-pressure days, especially cold ones, an entire attic can be on fire and the occupant might only smell a slight odor of smoke. I have seen this myself – smoke and flames were shooting 30 feet in the air out of a woman's roof, and neither she nor the neighbors had any idea. It was a cold, crisp morning, and all of the products of combustion were being lifted away and sent through the fields of Ohio. 

It also works the other way. In summer, when the air is so thick you can taste it and the tea glasses sweat before they get placed on the napkin, you really notice atmospheric pressure and concentration. Many a summer night we pulled onto a street, looking for a reported house fire, and found nothing but a wall of smoke with no clear indication as to which house was on fire. The smoke hung so low on some of those mornings that we mistakenly kicked in the wrong door! 

The bottom line is that low pressure can make life tough for firefighters and confined space entrants alike. 

Is Your Meter Protecting You?

I have learned a lot about meters the hard way. That site safety manager dropping before I even knew there was a problem is a fine example. How could this happen? Simple: It takes the meter's pump 1 second to pull its sample through every foot of hose. On this meter, we had at least 20 feet of hose. That puts you at least 20 seconds behind. On a passive meter, it takes up to a minute to read the concentrations of ambient air. 

The meter you are using may not be giving you very timely information on its best day. On its worst day, it may not be calibrated properly or have a fully charged battery. It has been my experience that meters that are left in the hands of field workers and tool crib managers to be calibrated and maintained usually are out of compliance. It takes time, training and expensive calibration gas to keep these meters in fighting form. For those reasons, it doesn't always get done. 

Another option is renting a meter from a reputable dealer that guarantees the meter has been maintained and calibrated by experts in fresh air environments.

Difficulty Breathing

If I were going to write a book about emergency preparedness, it would be called "Difficulty Breathing." When I teach hazardous materials classes, I always a simple question. Many of the participants are educated in science – nurses, paramedics, doctors and the like, but no one ever knows the answer: "How many times did you breathe in the last minute?" 

No one can ever answer precisely, even if they can guess within the standard: "Ten to 12 times?" They never know for sure, and that is the point. The respiratory system is so impressive that we never worry about it. We take in a variety of gases by creating negative pressure, separate out the oxygen and infuse it into our blood, a liquid. From there we pick up the waste products of the Krebs cycle, carbon dioxide and water, convert them back to a gas and exhale them. 

As far as this humble firefighter is concerned, the process truly inspires awe. We never even notice we are breathing unless we are having a problem (or doing yoga). That is the beauty of it. In fact, it takes a heart-lung pump and room full of people wearing scrubs to make that process happen outside of the body. 

  Our bodies provide a top-notch air intake and proportioning system, but as soon as it’s out of calibration, our lives are at risk.

The point is that we have been given a top-notch air intake and proportioning system. We know that as soon as it is out of calibration, assuming we don't fix it immediately, we'll die an untimely death. 

So workers, rescuers and John Q Publics, listen up! Get up wind, cover your mouth and nose and wear your PPE. If you are using meters to protect yourself or others, make sure they are charged and calibrated properly and that you understand their limitations. 

Adam O'Connor is a 16-year veteran and captain of the Fort Wayne Fire Department, a hazmat and tech rescue technician, a registered nurse and a regional manager for Niles Safety Services.

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