Thursday, November 12, 2015

Non-Toxic Gases Kill

There was a short news item on this afternoon about an industrial accident that killed one employee. The report notes that a CO2 gas leak at the facility was responsible, explaining:

“Alarms immediately sounded when the leak happened, and employees responded properly, but a man who was closest to the leak was affected, HFD [Houston Fire Department] said.”

While there is a great deal in the news about the release of CO2 to the atmosphere as a probable (or not depending on your political suasion) cause of global climate change, there is very little talk about this being an industrial chemical that is used in a number of different commercial applications, from industrial cooling, to atmospheric deoxygenation, to caffeine removal from coffee.

CO2 at room temperature is a non-toxic gas that is a routine part of the air that we breath every day and an important part of the respiratory cycle for the exchange of oxygen between plants and animals.

So, if CO2 is non-toxic and necessary for life, how did a person die from a CO2 leak? The answer if fairly simple; asphyxiation. The atmosphere contains a number of chemicals, but the most important one from an animalistic point of view (and please remember that humans are animals) is oxygen. Oxygen is typically found in the air at about 21%. Anything below about 19% starts to become too little to support life. As other gasses are added to the atmosphere the amount of oxygen (as O2) starts to decline. If too much is added to the local area, then there is not enough oxygen present to support life and animals die.

Apparently what happened here is that there was a leak, probably in a CO2 transfer line. The facility had some sort of alarms in place (probably based upon O2 sensors), but the person closest to the leak did not apparently have time to evacuate to a place of high-enough oxygen concentration and died.

Short of requiring employees to carry O2 cylinders all of the time (expensive and not without their own level of hazard) there is not much that can be done to prevent this sort of accident, except ensuring high levels of ventilation. If you move high amounts of fresh air through areas of the facility where leaks can be expected to occur (and CO2 leaks should not happen often; it is a relatively inert gas) you greatly reduce the probability that unsafe concentrations of CO2 can occur or last long enough to kill employees.

One relatively simple way to do this is to keep all CO2 transfer lines on the outside of the building, normal air movements should serve to keep ambient O2 levels high enough in the event of a leak. In areas where transfer lines must traverse enclosed areas of the facility emergency ventilation fans (tied to O2 sensors) may be necessary to flood the area with outside air to displace the leaking CO2. In areas where such ventilation is not necessary emergency O2 bottles can be placed to allow anyone in such areas to get oxygen before the pass out (2 to 3 minutes after being in a depleted O2 environment).

It is way too early in this incident to tell what precautions had been taken by the facility owner to prevent this type of incident. The presence of alarms would seem to indicate that the employer was aware of the hazards, and it is possible that even if all reasonable precautions had been put into place that unusual circumstances were in play in this case.

A detailed investigation is going to be necessary to determine what happened and what could have been done to prevent it. Since a death from chemical exposure was involved, we might normally expect that the Chemical Safety Board (CSB) would investigate this accident. Recent news stories, however, have reported that the CSB does not intend to initiate any new investigations until their current investigation backlog is erased. We will probably hear more about this at the public CSB meeting later this month in Washington.

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