Nitrogen Cloud

The news story is a bit dated, coming from the first part of the month, but it illustrates a basic problem that we have with emergency response in this country; a lack of chemical knowledge on the part of responders and their supervisors. And worse a lack of chemical emergency response planning.

Cryogenic Nitrogen

The story is fairly straightforward. A cryogenic nitrogen tanks begins to leak. ‘Cryogenic Nitrogen’ is simply nitrogen gas cooled and compressed until it becomes a liquid, increasing the amount of nitrogen that can be stored in a given tank size. As the liquid nitrogen exits it tank it almost instantaneously converts into a gas. It is quite cold so it makes any water vapor in the air condense and form a white cloud.

Nitrogen is a colorless and odorless gas. It is not toxic; it better not be because it makes up over half of the composition of the air that we breathe every day. A nitrogen leak is hazardous for two reasons. First in the immediate vicinity of the leak the temperature is well below 0° C and can cause cold related injuries. In a slightly larger area around the immediate leak the concentration of Nitrogen can get well above 80% at which point there is not enough oxygen in the air to support human brain function.

Emergency Response

The problem identified this news story is the actions of the local fire department when they arrived on the scene. They apparently knew that they were dealing with a nitrogen leak. They evacuated the building closest to the leaking tank, a reasonable but probably unnecessary precaution. Excessive caution is commendable trait in an emergency response situation.

They then became concerned about the spreading white cloud. For some reason they assumed that it was a cloud of nitrogen gas (odorless, colorless remember?). As the cloud approached two off-site buildings, they ordered the evacuation of those buildings as well. This disruption was certainly not called for even given any reasonable measure of excess of caution. Okay, we’ll just write it off as unreasonable excessive caution, still probably not a real bad thing.

No, the silliest thing that they did was described this way in the article: “Firefighters dispersed the vapor cloud with a hose stream.” Yes, it was a cloud, not a cloud of nitrogen gas, not even a vapor cloud; just a cloud, condensed water vapor in small droplets. The same kind of cloud we see most every day high in the sky overhead. The only danger with the cloud is that it impedes visibility.

Now the atmosphere in that cloud was certainly nitrogen enriched, but their hoses did nothing to change that. The water couldn’t absorb or dissolve any of the nitrogen, it was already saturated in nitrogen from the atmosphere. It couldn’t chemically neutralize the nitrogen, atmospheric nitrogen is practically non-reactive. So, removing the cloud didn’t make the area any safer.

No, the only thing they could have done to protect the populous was to measure the oxygen concentration of the air downwind of the leak. That way they could have established a reasonable safe zone around the leak and assured the surrounding public of their safety. And it wouldn’t have taken “two fire engines, two ambulances, a HAZMAT vehicle, ladder truck, battalion chief and two deputy chiefs”.

Emergency Response Planning

Don’t get me wrong. I have the greatest respect for fire fighters and other emergency response personnel. They are extremely brave and selfless and one of the most under paid civil servants in this country. The ‘proper’ response to this situation is obvious to me because I am a chemist and I worked at a facility with one of these cryogenic nitrogen tanks. We had worked out this emergency response plan for our tank as part of our general facility hazmat response plan.

Our plan did call for notifying the local authorities of a significant nitrogen leak, but with the comment that we did not need any assistance (unless we had had someone injured in the initial leak). The plan called for a local evacuation, oxygen level monitoring and then contacting the owner of the tank to fix the leak and re-fill the tank when it was emptied. Oh, yes, and shut down all of our processes that required nitrogen.

The advantage of having an emergency response plan is that you know what to do in the event of an incident. We practiced our plans so we reacted in a practiced manner.

We did our planning with the local fire department for emergencies that would have an off-site effect or would require their support to respond to. And they took part in exercises with us on an annual basis. They understood the chemical hazards they would face when they rolled through our gates and understood their part in the response. We never did require their assistance on any real incident in the 16 years I worked at that plant, but we knew that they would be there as part of the team if and when.

And nobody would use water hoses to knock down a cloud.