what happens if that large enclosure fails and the CO2 freely flows outside?

That enclosure has a huge volume - area the size of several football fields, and at least 15 stories high. The article says it holds 2k tons of co2, which is ~1,000,000 cubic meters in volume.

CO2 is denser than air will pool closer to the ground, and will suffocate anyone in the area.

See https://en.wikipedia.org/wiki/Lake_Nyos_disaster

Edit: It holds 2k tons, not 20K tons.

CO2 is in general less dangerous than inert gases, because we have a hypercapnic response - it's a very reliable way to induce people to leave the area, quite uncomfortable, and is actually one of the ways used to induce a panic attack in experimental settings.

If it were, say, argon, it would be much more likely to suffocate people, because you don't notice hypoxia the way you do hypercapnia. It can pool in basements and kill everyone who enters.

That being said it is an enormous volume of CO2, so the hypercapnic response in this case may not be sufficient if there's nowhere to flee to, as sadly happened in the Lake Nyos disaster you cited.

Company says safe limit is 70 meters, about 200 feet.

Easy to build infra and other stuff that far away, especially in locations where this is meant to be used.

There are many aspects of safety

1. If the puncture is due to hurricanes, etc, the danger is non existent. The hurricane will blow away the co2 in no time.

2. If the puncture is due to wear and tear, then the leak will be concentrated and localized. It could naturally diffuse.

CO2 meters can be installed around the unit for indication.

Oxygen masks can be placed around the facility for emergency use.

The dangers are very much mitigatable.

The last section of TFA is called "What happens if the dome is punctured?". The answer: a release of CO2 equal to about 15 transatlantic flights. People have to stand back 70m until it clears.

It would not be good, but it wouldn't be Bhopal. And there are still plenty of factories making pesticides.

Yeah, I was also immediately thinking about the Lake Nyos disaster. But that one released something like 200k tons of CO2 in an instant, whereas this facility has 2k tons, which would more likely be released more gradually.

So .. significantly less dangerous than a corresponding volume of natural gas, which is also unbreathable but also flammable/explosive?

> People will also need to stay back 70 meters or more until the air clears, he says.

I wonder whether it'd be possible to augment the CO2 with something that would make it more detectable visually and aromatically, like we do natural gas.

Natural gas is naturally odorless and colorless. Therefore, by default, it can accumulate to dangerous levels without anyone noticing until too late. We make natural gas safer by making stink, and we make it stink by adding trace amounts of "odorizers" like thiophane to it.

I wonder whether we could do something similar for CO2 working fluid this facility uses --- make it visible and/or "smell-able" so that if a leak does happen, it's easier to react immediately and before the threshold of suffocation is reached. Odorizers are also dirt cheap. Natural gas industry goes through tons of the stuff.