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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:
Nitrogenfree.com -->)
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.
References
CSB: Valero Refinery Asphyxiation Incident
CSB Safety Video: Hazards of Nitrogen Asphyxiation
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