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The Most Dangerous Industrial Gas

Posted August 15, 2012 12:00 AM by cheme_wordsmithy

Among hazardous chemicals and substances handled in industry, gases are often the most dangerous. In addition to being harder to contain than liquids or solids, many gases are invisible and odorless, forcing workers to rely on sensors and meters to detect leaks.

But surprisingly, amongst all the toxic, corrosive, and otherwise nasty gases that exist in industry, the most deadly of them all is the one we breathe in the most - nitrogen.

(Credit: -->)

Nitrogen (N2) is an inert and invisible gas that makes up about 78% (by volume) of the air we breathe. The lungs don't absorb any of it, and it comes right back out when we exhale along with carbon dioxide (CO2), as discussed in ChelseyH's newest Medical Mystery blog post. No interactions, no suffocation, no problems.

Nitrogen Asphyxiation

But don't let that fool you. Things get dangerous fast when nitrogen concentration rises and oxygen levels fall in a closed environment. It only takes about a 2% dip from normal oxygen levels to create a breathing environment that is fatal within a short period of time. Victims of nitrogen-rich environments often don't know what's wrong until it's too late, because normal breathing is still taking place; carbon dioxide is still being released, so the buildup which causes suffocation doesn't happen. The incident, termed 'nitrogen asphyxiation', results in a lack of oxygen which impairs judgment, coordination, and the ability to exert strength. In extreme cases, even just one breath can result in unconsciousness.

Just how prevalent is the nitrogen problem? Accidents involving nitrogen asphyxiation cause nearly 8 deaths per year in the U.S. The CSB (U.S. Chemical Safety and Hazard Investigation Board) reports that between 1992-2002, 85 incidents occurred, resulting in 80 deaths and 50 injuries. Of these, perhaps one of the most tragic was an accident at a Valero Refinery in Delaware City, Delaware.

The Fatal Valero Asphyxiation Incident

On the night of November 5, 2005, a pipe elbow had been removed on the top of a hydrocracker which was shut-down for maintenance. Nitrogen had flowed into the reactor and exited from the covered opening, which was marked with a "Danger: Confined Space" sign but had no signs for nitrogen hazards. Nitrogen dangers in the report for the installation crew had been marked N/A.

(Credit: CSB)

Down in the opening, workers noticed a roll of duct tape in the reactor, which needed to be removed in order for work to continue. However, entering the reactor to remove it would require obtaining a special crew and permit, which would cost a lot of time and money. This was incredibly inconvenient considering the reinstallation was scheduled to be completed that night, and a crane needed for the operation had just become available for that short window of time.

In an attempt to save time, a worker tried retrieving the tape with a long wire, but to no avail. There are two plausible scenarios of what happened next: either the worker got close to the edge of the reactor hole, or he decided to climb down into it. In either case, in an attempt to retrieve the duct tape the worker ended up breathing in oxygen-deprived air and quickly collapsed down inside the reactor.

An eyewitness saw that the foreman and a contractor were peering down the hole when the first worker collapsed. The foreman quickly grabbed a ladder, inserted it into the hole, and climbed down to attempt a rescue. He too collapsed inside the reactor. The contractor then quickly declared an emergency on his radio.

Over 10 minutes since the first victim collapsed, emergency crews had responded and found the oxygen levels within the hole to be below 1%. Using breathing apparatuses and harnesses, they retrieved the workers from the reactor, but attempts to revive them were unsuccessful. It was later estimated that the men died around 3 minutes after falling unconscious within the reactor.

Lessons Learned

In an investigation of the incident, the CSB determined that current industry safety guidelines, company training programs, and OSHA standards were not enough to adequately warn workers about the dangers of low-oxygen hazards. Properly informed and trained workers would know not to enter such confined spaces without safety equipment such as oxygen level meters to detect O2-deficient environments. They would also know not to attempt a rescue of a fellow worker without essential breathing equipment or first purging the area of the harmful gases.

(Credit: RKI Instruments -->)

As always, industry should strive for safety as a number one priority in any potentially dangerous work environment. Nitrogen-related accidents like that at the Valero refinery can be prevented through proper safety equipment, thorough reporting, adequate warning signs, and sufficient training in the workplace.


CSB: Valero Refinery Asphyxiation Incident

CSB Safety Video: Hazards of Nitrogen Asphyxiation


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Re: The Most Dangerous Industrial Gas

08/15/2012 12:57 AM

"the CSB determined that current industry safety guidelines, company training programs, and OSHA standards were not enough to adequately warn workers about the dangers of low-oxygen hazards."

I know the article says Delaware, but on what planet? I wrote entry permits and worked in confined spaces for many years. OSHA standards clearly state any confined space must first be tested for adequate O2, (and other gasses too), before entering. Workers must also be equipped with meters at all times. OSHA also requires ongoing training and testing for every worker. These workers clearly were not trained correctly, at the fault of the employer.

If you have to enter an industrial confined space, demand your employer follow OSHA standards, (or get a canary for your sidekick).

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Re: The Most Dangerous Industrial Gas

08/15/2012 11:09 PM

GA these regulations have been around for years. I work in the construction and mining industries for over 16 years. Permit are not expense, equipment isn't expensive, and training isn't expensive. Losing ones life is expensive.

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Re: The Most Dangerous Industrial Gas

08/15/2012 4:36 AM

At a primary pharmaceutical factory in the late 1990s, three electricians had been working in a building that was shut down for maintenance with a copy of the general permit affixed to each entrance door of the building, warranting that all utility fluids were isolated. Carrying out their own electrical isolations as needed under a separate Permit To Work, the individuals left the site that evening, checking-out at the automated turnstile using their name-registered passes and taking their passes with them. All in order so far.

When they got back to their head office, they handed their turnstile passes to three mechanical technicians, who used these passes the next day to gain access to the site. These three failed to notice that the general permit had been withdrawn from the entrance doors, the building being worked-up overnight for production again, and proceeded to a 12m3 agitated stainless steel reaction vessel with a mind to re-attach the agitator impeller to the bottom of its shaft inside the vessel. One of the three was just about to climb into the vessel using a rope ladder slung through the upper access way when an eagle-eyed operations supervisor stopped them and challenged them. He may have saved their lives by so doing.

Under slightly different circumstances, unknown to the technicians, the vessel would have been full of nitrogen when they entered it. There was no record of these three individuals being on site, and in this scenario the first anyone would have known that there was anything wrong would have been off-colour and off-spec product with a strange smell some days later. One wonders what the reaction of their grieving families and friends may have been.

Confined Space Entry Procedures are there for a reason.

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Re: The Most Dangerous Industrial Gas

08/15/2012 8:32 AM

On a slightly different industry (farming) but just as important, nitrogen dioxide is wide spread and is dangerous for a number of reasons if not taken seriously, usually seen on the farms animal feed storage facilities (Silos) Even though it is accompanied by a bleach like smell, with a yellow or dark brown gases. Also known as silo gas.

A farmer can open up a silo, and work in this environment with little problems and but die several hours later in his sleep with a buildup of fluid in his lungs. I do not know why the AG Extension offices do more to educate the farmers on procedures to work in confined spaces. When opening up a silo, we had always a spotter, as well as setting up and running the blower to ensure a fresh air supply, but it was still gassy in the silo. Looking back we may have taken precautions but if the entry person goes down, we would have been screwed. Because we had no plan for that. And we were typical.

This danger alone comes in second on the farm to the gases formed from manure storages facilities that take even more lives quickly.

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Re: The Most Dangerous Industrial Gas

08/16/2012 2:16 AM

There are some glitches in this article:
1. Nitrogen is not inert; it forms lots of compounds.
2. There is nothing special about nitrogen; any nonirritating gas would do in this context.
3. The distinction, if any, between suffocation and asphyxiation was not clear.
4. The problem is the absence of oxygen, not the presence of a normally harmless gas.
5. How were the OSHA standards inadequate? Had they been followed, how would this have happened?
6. How many deaths per year happen from other industrial gases (ammonia, chlorine, etc.)?

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Re: The Most Dangerous Industrial Gas

08/21/2012 5:01 PM

Regarding #6- probably the cumulative total is still less than the annual # of fatalities due to aspiration of the liquid form of dihydrogen oxide......unfortunate that all of these aren't less than they are!

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Re: The Most Dangerous Industrial Gas

08/16/2012 5:04 AM

I am with Tornado here. The claim that Nitrogen is the MOST dangerous industrial gas is only valid if we limit the definition to confined spaces where it's use in blanketing is extensive. Nitrogen used for cryogenics is hazardous for freezer burn but is not treated as a toxic gas. Having worked extensively with chlorine and ozone I would nominate both as more toxic. Chlorine is probably less dangerous because it's odour alerts it's presence. Ozone is odourless and it is toxic at ppm concentrations in free air. It is not as widely used as nitrogen and this probably accounts for the lower death toll, but ozone is slowly replacing chlorine as a disinfectant gas in some areas of the water treatment sector, the death toll will rise.

p.s. The Niels Bohr quote should surely have "...and have survived" added.


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Re: The Most Dangerous Industrial Gas

08/16/2012 7:36 AM

stick to the rules hard and fast and get it into your mentaility so its applied without any "slackadaisical" exceptions on those "rushed days "

I was called to do a welding job on a tank at a sewerage processing plant . I arrived and asked if the tank had been checked for gases.

i was told it had been tested but the engineer seemed a bit vague when he said it so i pushed the issue and asked who tested it , his reply " she'll be right mate "

the site safety officer arrived and i asked him if the tank had been tested he said sure yeah it will be okay you're only welding on the outside of the tank right ... but we can test it if you like ?

I asked him to do it and the test showed 18 % methane

( methane will explode between 4.4 % and 17 % depending on temperature)

i jumped back in my truck and drove away saying i would send them the bill for the wasted trip and to ring me when they had drained , washed and purged the tank with blowers prior to my next visit The thing that blew me away ( pardon pun ) was the site SAFETY OFFICER didnt give a rats about my life or his job , and the engineer should have known better too.

thanks me , for my wonderful intuition :)

moral of my story , trust your gut and stick to the rules by the letter


ps , another horror story for those of you who dont have enough gray hairs yet , i saw a story on the news here many years ago ( Australia )

two welders were on a site welding brackets to a full tank of waste engine oil .

Now the joke here is the brackets were required for a ladder , requested by the safety comittee so people wouldnt get injured climbing up to check the level guage So of course , the tank blew up and the two guys not only got sued and went broke but they were burnt so bad they couldnt work again for at least 6 years or so.

Any of you that thought engine oil is safe , there is a heads up for you

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Re: The Most Dangerous Industrial Gas

08/16/2012 8:04 AM

When people give you an weak answer, it has to be question.

Some goes for a strong answer.

That engineer would have needed to give you an entry permit. The responsibility is on his head. But, with a choice I'd rather have my life, than have that on that imbecile head.

Pricks like that pi$$ me off.

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Re: The Most Dangerous Industrial Gas

08/18/2012 3:21 PM

Argon can present less obvious low oxygen spaces when there is a lot used on a site. A friend of mine claims to have had a cigarette save his life at Diablo Canyon when they were doing all the Stainless. He was in a shoulder deep pit in a basement. Lit a cigarette, hit on it, and let it drop to his side. The second time it went out doing that, it dawned on him that there was no oxygen in the space just below his neck. The pit proved to be full of nearly pure argon. Since argon has nearly twice the density of air or nitrogen, it accumulates in low places. Beware!

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