How Dangerous is CO2 Build-Up in a Confined Space?

Factual Questions
1

I work in logistics for a large clinical lab company. We routinely use dry ice (frozen CO2) for transporting frozen specimens. I recently took an annual safety training course on handling dry ice. It included warnings that I do not recall every encountering before.

The training course claimed that a build-up of CO2 in a confined space, and specifically when used for specimen transport in a vehicle, is potentially hazardous. The training material didn’t actually specify what the hazard was, but the idea seemed to be that sublimating dry ice could lead to a high enough concentration of CO2 to create some sort of respiratory hazard.

The SOP, presented as a company requirement, was that when operating a vehicle that contains dry ice, the air recycle must be turned off, the A/C must not be set to “Max A/C”, and windows must be open at least 1". This was very explicitly not an SOP for transporting large bulk quantities of CO2, which we don’t do, but for the small amounts (10 pounds or less) we use for transporting frozen specimens.

For more context: we typically drive small to midsize cars as courier vehicles (Chevy Trax, Jeep Patriot, and Subaru Forrester are the three types in our local motor pool). We put dry ice in a styrofoam cooler in our rear cargo area. I’ve never precisely measured the quantity I use, I just eyeball it. At a rough guestimate, I might put about 5 pounds of dry ice in the cooler at the beginning of the day, and expect to have about half of it left by the end of the day, sometimes maybe a quarter. So, somewhere around 3 pounds of dry ice, give or take, sublimating in my car over 8 hours. That’s a very rough estimate of the weight - I might be off by a factor of 2, in either direction.

I have never followed the above SOP regarding ventilation. I drive with windows sealed, and, in the summer, with with the air recycle on and the A/C set to Max. Is whoever wrote the training material full of hot air, or have I been risking my health and/or life every day for the last 15 years?

2

I can’t link from my phone, but a man’s wife and his mother recently died from being in an enclosed vehicle too long with his dry ice while on rounds to refill his frozen treats business. In Tacoma, iirc.

3

Seattle Times article: Dry ice exposure leads to death of Dippin’ Dots deliveryman’s mother in Pierce County.

4

Thanks. I googled “tacoma dry ice death” and found several articles on the incident. One, from the Seattle Times, included information on several deaths attributed to dangerous concentrations of CO2. All of the cases cited seemed to involve much larger quantities than I deal with, or very different circumstances, and even then they are apparently very rare, but not unknown. So, it looks like this might have more validity than I initially thought.

BTW, the first article I clicked on, from “The News Tribune”, cited the University of Washington’s Department of Environmental Health and Safety on the hazards of dry ice, with a link. I clicked on the link, thinking it would lead to information on research conducted by the university on the hazards of dry ice. Instead, it leads to what appears to be a boilerplate workplace safety brochure intended for internal dissemination to U of W employees :smack:.

5

I happen to design industrial control equipment for a living. As such, I have done work in a lot of major breweries over the years. CO2 is a major risk in breweries.

CO2 is particularly dangerous because it is heavier than air, so it will settle into confined places and stay there. You don’t realize that it is there until you go into that area, and often you don’t get much warning at all before you pass out and asphyxiate. So the line between “everything seems fine” and “passing out and dying a short time later” is a very small line. You can go right up to that line and at the most feel a bit woozy, but most people don’t recognize that their brain functions are starting to get impaired due to oxygen starvation.

One of my co-workers almost died because he was down in an equipment pit. Fortunately, he felt a little woozy and immediately recognized what was going on and got out of the pit. If he had stayed in the pit, he would have died.

In an enclosed vehicle, the CO2 will settle at the bottom, so up near the top where your head is you’ll be fine until the CO2 reaches that level. Accelerate, and the CO2 will move towards the back of the vehicle. Decelerate or stop and all of the CO2 will rush forward, possibly enveloping your head and making you pass out. Slump down while you are passed out, and you’re dead.

Go downhill, and the CO2 will settle at the bottom of the vehicle, again, possibly covering your head. You get woozy, start to lose consciousness, and go off the road.

Drive around on level ground with little deceleration and the CO2 level could get all the way up to your neck and you’d never notice. So you could be very close to death and never realize it at all.

How close were you actually to death? Probably no way of knowing without actually measuring the CO2 concentrations in your vehicle after 8 hours. One pound of dry ice produces roughly 8 cubic feet of CO2, so 3 lbs, give or take, produces somewhere in the neighborhood of 24 cubic feet of CO2. A typical vehicle these days probably has somewhere between 60 and 100 cubic feet of interior space. My guess is you weren’t in any danger of asphyxiation while driving around on level ground with little stopping or deceleration. You could have potentially lost consciousness or have been impaired enough to cause an accident if you decelerated enough though. And if your vehicle is “leaky” then there would have been even less of a risk.

Your company’s SOP sounds reasonable to me.

By the way, if you want to see how quickly heavier air moves around in a car, this video demonstrates the effect pretty well using a helium balloon and just the different density of air at the very slight difference in altitude between the top and bottom of the vehicle. Just picture all of that CO2 down around your legs rushing forward and upward just as quickly as that helium balloon moves backwards.

6

Hypoxia is a sneaky killer. If you’re lucky, you might feel a bit tired, but most often, people just peacefully nod off and die. You’ll have very few seconds to realize what’s going on and find breathable air. As mentioned above, dry ice has killed at least one ice cream vendor, and it has caused at least one cargo airliner crash.

If you want a really wild hypoxia story, look up the death of golfer Payne Stewart. Pilot error led to cabin non-pressurization and the Learjet went off on its own from Orlando to Aberdeen, South Dakota as a “ghost” flight. Everyone nodded off as the plane climbed to cruising altitude and were dead long before the plane ran out of fuel and crashed.

7

Another thing that people often don’t realize is how quickly you can lose consciousness when breathing in an atmosphere with insufficient oxygen. You might think that you are in not much danger because you are capable of holding your breath for 30 seconds or more, and simply could exit the area. The problem comes when you inhale the “bad” air and it replaces the “good” air in your lungs. It only takes a few breaths of breathing in “bad” air to promptly lose consciousness. If you are then are unconscious in an area with “bad” area, you will never wake up. Irreversible brain damage follows a few minutes later, followed by death.

8

Well, since I’m getting in and out of my vehicle multiple times during the day, and opening the back hatch multiple times a day, it’s pretty darn leaky over those 8 hours. I have no idea how quickly the excess CO2 dissipates into the outside atmosphere when I have the door and/or hatch open, but I’ve got to have at least some “loss” of excess CO2 over those 8 hours.

I knew high concentrations of CO2 could be dangerous, I just didn’t think the relatively small amounts we deal with, in the relatively well-ventilated conditions of a car, would be much of a danger. The risk factor does seem higher than I initially thought. Still, with all of that glass, a car is effectively a portable greenhouse. Driving around North Carolina in the summer without the A/C maxed out…:(. I seriously think the risk factor from the heat would be non-trivial.

Either way, thanks for the reply.

9

From time to time, I do safety reviews for plants manufacturing or using Industrial gases at large scales. CO2, Nitrogen, Argon, Helium etc. are all inert gases and pose asphyxiation hazards in confined spaces. They are specially dangerous because the victim gets no warning or signs.

As to your company’s SOP - it will totally fail in my review and here is why : When control or alarming sensors are available, it is usually good practice to use them. Relying on human actions to ensure windows are cracked or AC is not in recycle etc. should not be the only line of defense. What if it is raining and the victim decides to shut the window ? What if there is a cloud of dust up-ahead and the victim decides to put the ac on recycle mode ?

So my recommendation would be to install Oxygen Deficiency Monitors in each transportation vehicle or provide employees with personal monitors/alarms. Depending on the type, you can get these monitors for as cheap as $100.
Here are some monitors for your consideration (simple google products search).

10

Adding to my previous post :

In my experience, when working with smaller companies the simple question - “Are your insurance guys aware that you are using only human controls for a life/death risk when off the shelf products are available ?” usually does the trick. Larger companies are risk averse and often have Best Available Control Studies.

11

Please post the link to the video. Sounds very interesting.

As a general rule, I advise chemical plant operators to not think of gases like they think of liquids. If its a closed room, and you pop a hydrogen balloon - the hydrogen will not rise to the top of the room, in-fact you can take a gas sensor and you will measure the same concentration of Hydrogen everywhere in the room. This is because hydrogen diffuses very easily due to its small molecular size. This happens in a matter of seconds.

Diffusion in ambient air depends on temperature and plays a bigger part than density of the pure gas. It is therefore not advisable to make conclusions if a light gas will go to the ceiling or a heavy gas will settle to the bottom when personnel safety risks are involved.

12

I think people seriously underestimate the risks of dry ice.

We sell it where I work (big box store). The cooler it’s kept in very clearly says not to handle with your bare hands. We’ve had at least one employee suffer a cold injury from ignoring that sign (fortunately it was minor and she healed up without long-term effects). Folks thought I was over-reacting when shooing kids away from it - they were taking turns sticking their heads down into the cooler to breathe the “fog”. Og knows what people who buy it get up to.

I’ve used it for cooling when I lacked power and a working refrigerator - I kept the cooler in the front room and me and the birds in the back bedroom, and definitely kept the birds away from it as they are far more prone to hypoxia than humans are. That is, after all, why canaries were used in coal mines.

13

I thought I did link to the video. Whoops. :slight_smile:

14

In large quantities, carbon dioxide can of course cause death by asphyxiation merely by displacing oxygen. It’s no different from inert gases in this regard. However, carbon dioxide also can be hazardous (even fatally so) at seemingly low concentrations. Dilute the atmosphere in your car with 8% helium? No problem, you’ll just feel like you’re in Denver. Dilute the atmosphere in your car with 8% CO2? Hope your will is up to date. Concentrations much lower than that can still cause troubling physiological symptoms and mild cognitive impairment that could lead to a crash. This publication points out a hazard associated with having multiple occupants in a car with the HVAC on recirc for extended periods.

If I were transporting several pounds of dry ice in a cooler, I’d follow that SOP.

15

[quote=“engineer_comp_geek, post:13, topic:831638”]

I thought I did link to the video. Whoops. :slight_smile:

[/QUOTE]

Thanks for the video engineer_comp_geek. I didn’t expect the balloon to go forward, but it makes sense. Ignorance fought yet again .

16

In the Apollo 13 near disaster, CO2 buildup was a major issue. In fact, they had to build a makeshift filter on board in order to survive.

17

[quote=engineer_comp_geek]
I thought I did link to the video. Whoops.

[/quote]

With a homogeneous atmosphere in the car, it doesn’t take much relocation of mass to establish a new density gradient vector. When you slam on the brakes, you won’t detect a breeze as air near the floor rushes toward your feet (and air near your head rushes to the rear of the car).

But it’s different when you’ve got a layer of CO2 near the floor. That layer will have some momentum, and under aggressive braking, it could very well slosh upward at the front of the car well beyond its equilibrium height, just like an inch of water will slosh up high on the inside of a pot you are carrying if you stop suddenly. It’s a bit like the classic oil+water desktop wave machines.

18

Yes. In fact, reading this thread made me want to ask a tangent question of engineer_comp_geek: How are CO2 filters (like those used in spacecraft) engineered to account for the differing densities of CO2, pure gaseous oxygen, and plain air? I had always assumed fans or something anaolgous … but fans might not help much if all the CO2 is “hiding out” somewhere low.

Tangent 2: Are there engineering commonalities between CO2 scrubbers used in spacecraft and those used in earthbound industrial settings?

…

gdave:

In your particular situation … I think I’d just run the non-recirculating A/C with the windows cracked open 1" when dry ice is on board. Not the most fuel-efficient use of the vehicle, but not all that bad either.

19

I am having a hard time believing that CO2 settles in layers as I pointed out in my last post.

The scale height (Scale height - Wikipedia) of air is around 8 km (5 miles). Simplistically this means you need a room about 5 miles tall before you see concentration differences between the top and bottom.

Granted air has a molecular weight of about 29 and CO2 has about 44, but still the chamber will need to be over a mile tall to see “a sloshing layer of CO2 at the bottom”.

20

Didn’t you see Apollo 13? I think 14% CO2 is fatal. It’s odorless and colorless. If in doubt, ventilate.