“It is these properties that make materials so useful that also pose hazards to health and property.” — Peter Lodal
Liquid nitrogen has some wonderful properties. It is really, really cold, so it is great for flash freezing delicate items. When vaporized, it helps maintain non-flammable mixtures, even when flammable vapors are present. Because it is extracted from air, which itself is 79% nitrogen, and is non-toxic, it poses absolutely no environmental or global warming hazard when it is released back into the atmosphere.
But it is not harmless. Just ask the folks at the Foundation Food Group’s Gainesville Plant 4.
What Happened in Gainesville?
The Chemical Safety Board (CSB) is investigating the incident, and it will be some time before they release a final report. Nonetheless, they have been issuing updates and a reasonably clear picture is emerging. Gainesville Plant 4 began switching over from an ammonia-based refrigeration system to a liquid nitrogen system in 2020. It uses the system to flash freeze processed chicken before packaging. On Thursday morning, January 28, 2021, there was a release of liquid nitrogen inside the plant at production line 4, one of five production lines in the plant. The liquid nitrogen vaporized. The boiling point of nitrogen is 77 K (-196 C, -320°F). Because the vaporized nitrogen was still very, very cold, it was denser than the ambient air and settled to the floor, displacing air upward.
Five people died at the plant. Thirteen people were hospitalized, one of whom died at the hospital. Another 130 people were evacuated. Among the dead were maintenance, supervisory, and management personnel.
What Didn’t Happen in Gainesville?
The most visible reminder that liquid nitrogen is in use at a facility is the cryogenic storage tank that is installed outside. This is where the facility receives truckloads of liquid nitrogen. When the facility is using the liquid nitrogen, the piping around tank is often heavily iced up. This is the equipment that many find frightening because there is so much there and failure while unloading could be catastrophic.
At the Gainesville plant, the liquid storage tank was installed outdoors, where the ventilation can be expected to be excellent. It is still up to the investigators to determine, but we can expect that they will find that the release was not related to the receipt or storage of liquid nitrogen. Instead, the failure was inside, perhaps with fittings or piping components.
Safety Checklists for Cryogenic Nitrogen
Liquid nitrogen is a known material with known hazards. We have found that the best way to address the known hazards of a well-understood process is with a checklist. A review of our own checklist for cryogenic service identifies a couple of safeguards that help protect against the hazards of simple asphyxiants that are worth mentioning here.
The first is to assure that there is adequate ventilation in the space where simple asphyxiants are being used. “Adequate ventilation” must be judged in the context of the size of potential release in relation to the volume of the space into which it would be released. Are the turns of fresh air sufficient to maintain a healthy oxygen concentration in the event of a release?
The second is to monitor the oxygen level in a space where simple asphyxiants are being used. Many facilities will install oxygen monitors that alarm or turn on warning lights if the oxygen concentration drops below a safe level. OSHA considers a concentration of oxygen below 19.5% to be a hazardous atmosphere.
People are often surprised at how few breaths of something besides air it takes to be fatal. Two breaths can be enough.
What? Just two breaths? But my normal breathing rate is 12 to 16 breaths per minute, you’re thinking, and even though I’m not a pearl diver, I can still hold my breath for over a minute. Surely, I can go without fresh air for more than two breaths! Holding your breath, however, is not the same as displacing the gas in your lungs with something that is not air.
We do not use the oxygen we breath in very efficiently. We breathe in 20.9% oxygen; we breathe out 16.4% oxygen. When we hold our breath, there is still oxygen in our lungs for our body to use. When we breathe in a simple asphyxiant, on the other hand, it displaces the already diluted oxygen in our lungs. Then, when we breathe in a second time, it dilutes it even more, to the point that unconsciousness can result for some, followed by death. Here are the effects of oxygen deficiencies:
- 20.9% O2 Normal
- 19.0% O2 Some unnoticeable adverse physiological effects
- 16.0% O2 Increased breathing rate, impaired thinking, reduced coordination
- 14.0% O2 Emotional upset, faulty coordination, poor judgment
- 12.5% O2 Impaired respiration, nausea, vomiting, permanent heart damage
- 10.0% O2 Inability to move, loss of consciousness, convulsions, death
Note that the simple asphyxiant doesn’t have to completely displace the oxygen-containing air. Displacing half of it can be fatal. And our bodies don’t detect the absence of oxygen. That pain you feel in your chest as you hold your breath is not your body telling you that there is not enough oxygen, but that there is too much carbon dioxide. But if you are breathing a simple asphyxiant, there is no accumulation of carbon dioxide for your body to sense and tell you that there is a problem.
When equipment fails, our instinct is to call maintenance. We never explicitly say, “The equipment is about to explode. Could you get over there so if it does we’ll be guaranteed a victim?” Instead, we ask, “I’m getting a reading that doesn’t make sense. Would you go check it out?” And maintenance technicians, being the can-do people they are, put themselves in harm’s way to troubleshoot and resolve the problems.
Most of the time, this works out. Maintenance fixes the problem, normal operation resumes, and all is well. It works out so frequently that we forget that maintenance is responding to an abnormal situation. Remember, though, that it is during abnormal situations that personnel are most vulnerable.
The personnel who died at Gainesville Plant 4 last week were not operations personnel overwhelmed by a sudden and random equipment failure that just happened to occur nearby. They were there responding to a problem and the problem overwhelmed them.
When the CSB issues the report of its investigation, we’ll learn what safeguards were in place at the Gainesville Plant 4. In the meantime, consider your own use of simple asphyxiants. Not just nitrogen, but argon, helium, hydrogen, methane, or any gas that is not toxic but is also not air. Sure, you can use them without incident. You do use them without incident. But what if something goes wrong? Are you ready for it?
There is a principle in dealing with bloodborne pathogens known as universal precautions. It requires that all blood be treated as though it known to be contaminated. It takes the guesswork out.
Likewise, you should treat all piping as though you know that at some point it is going to leak. Treat all abnormal conditions as hazardous. Who needs to be there to resolve the abnormal condition? Who could make just as valuable a contribution from a distance? The incident at Gainesville Plant 4 is a terrible tragedy. The best way any of us can respect those lives lost in that tragedy is to learn from it, be reminded of the hazards, and do what we can to prevent a reoccurrence of that tragedy in our own facilities.