Liquid Nitrogen Leak in GA Kills 6 – CSB Investigating

Earlier this week there was a liquid nitrogen leak at a chicken processing plant in Georgia that killed six people. Yesterday, Dr. Katherine Lemos, Chair of the Chemical Safety Board, held a press conference near the site to outline what the CSB knows at this point very early in their investigation. The New York Times has a good article on the incident.

The Incident

According to Lemos’ statement, the facility uses liquid nitrogen to flash freeze processed chickens on Line 4 at the facility. Somewhere (yet to be determined) between the liquid nitrogen (LN) storage tank and the cryogenic freezer where the LN is used, a leak occurred on Thursday. Upon release the LN warmed and converted to nitrogen gas, an asphyxiant. The plant was evacuated, but five people were apparently overcome and died on site. One was later pronounced dead at a local hospital. Twelve people were hospitalized and 130 people were evacuated from the plant site for medical evaluation.

CSB has identified the vendor that supplied the LN tank and presumably supplies the LN. It would appear from the Lemos statement that someone else designed and installed the supply lines to line 4 and the cryogenic freezer on that line. That equipment was installed and commissioned in the last 4-6 weeks according to Lemos. There are indications (tools on the ground near the equipment) that some sort of maintenance activity was on going when the leak occurred.

Lemos reported that the facility was receiving 2-3 truck loads of LN per day.

Liquid Nitrogen Background

LN is cryogenically stored N₂. Stored at less than -325˚F, the liquid boils when it is released to the atmosphere. During conversion to gas it expands to 640 times its original volume. The expanding gas will displace air (which is already mostly nitrogen gas), reducing the oxygen content in the area of leak to next to nothing. The size of the area affected by oxygen displacement will depend on the amount of LN released.

Moving LN through a facility requires specially designed and maintained piping and pumps. The extreme low temperature makes metals brittle. The contraction of piping due to the drop in temperature as LN moves through the piping and re-expansion after the movement is complete, will put stress on joints and elbows. Pressure will increase in piping as the temperature rises after LN movement stops, this requires well designed pressure venting systems.

Physical contact with LN by the human body will lead to injuries ranging from frostbite to flash freezing and potentially shattering of severely frozen body parts.

Commentary

I have never worked with LN for flash freezing. It has been used at chemical facilities where I worked as a source of nitrogen gas to make inert atmospheres above flammable liquids. In those cases, the vendor typically owns the LN storage tank and the evaporators that convert the LN to N₂ gas. They designed, oversaw the installation and were responsible for the maintenance of the LN tanks and conversion systems. The facility was only responsible for the gas system past the first output valve from the evaporators.

LN is tough stuff to work with, particularly with systems that are not always in contact with LN, presumably like piping and pumps. Having said that, this is not cutting-edge technology; the engineering and maintenance issues have been identified and solved. So have the safety aspects of monitoring and training response personnel and personnel that work around the system.

The thing of concern to me from the Lemos statement was the implication that some sort of maintenance work was being done on the LN system around the area of the leak. There is not much maintenance work that can be done on an LN line while it is delivering LN. If a line-break had been considered as an option during that work, the line would have been emptied and purged and that building would (should!) have been evacuated before such break should have been made.

It will be interesting what the CSB finds in their investigation. With all of the bad press that the meat processing industry has been receiving about working conditions during the pandemic, incidents like this immediately cause me to think the worst, and that is probably (hopefully) unfair.