What CO₂ Level Is Dangerous?

CO₂ is considered dangerous at 5,000 ppm (0.5%), which is OSHA’s 8-hour exposure limit and the point where safety alarms are set to trigger.

But there’s more to the story. Continue reading to learn all about CO₂ levels – and how to stay safe.

What Makes 5,000 ppm the Magic Number?

OSHA picked 5,000 ppm as their Time-Weighted Average because that’s where your body starts losing the fight – eight hours at this level means measurable performance drops, and performance drops mean accidents.

It’s not arbitrary. At 5,000 ppm, CO₂ is 12.5 times higher than fresh outdoor air (400 ppm). Your blood pH starts shifting, your breathing rate increases to compensate, and you experience drowsiness caused by your brain not getting enough oxygen.

Here’s the concentration-plus-time equation: 30,000 ppm for 15 minutes is OSHA’s Short-Term Exposure Limit. Drop down to 5,000 ppm and you “get” eight hours – technically legal, but your workers might not be functioning as well in the afternoon as they were in the morning.

Obviously, you don’t want a drowsy forklift operator or a confused worker in a confined space.

So, treat 5,000 ppm like your credit limit. Just because you can hit it doesn’t mean you should. 

How Fast Can CO₂ Levels Jump from Safe to Deadly?

In a failed ventilation scenario, CO₂ can jump from normal (1,000 ppm) to dangerous (5,000 ppm) in under 10 minutes, which is faster than most workers would notice that something is wrong.

Normal indoor air sits around 400-1,500 ppm. Comfortable, safe, nobody’s thinking about it. But seal off a 10×10 room with four people inside and no ventilation? You’ll hit 5,000 ppm before the morning meeting ends.

Let’s say a beverage cooler has a slow CO₂ leak overnight. By morning, it’s sitting at 30,000 ppm. Someone steps in to check inventory, takes a few normal breaths of that 3% CO₂ air, and the dizziness hits fast. A couple minutes later, they’re on the ground.

Also, it’s not just the speed – CO₂ is invisible and odorless, so you can’t sense danger approaching. One minute you’re troubleshooting a valve, the next minute you’re confused why you can’t remember what you’re doing.

The gap between “feels stuffy” and “can’t stand up” is measured in seconds, not hours.

What Happens to Your Body at Each CO₂ Level?

Below, you will learn what happens to your body at each CO₂ level:

What’s scary is that the progression isn’t gradual. You don’t slowly get more tired until you pass out. You’re functional, then impaired, then unconscious – and each jump happens faster than the last.

Which Industries Have a Higher Likelihood of Hitting Dangerous CO₂ Levels?

While any business that uses CO₂ is at risk of hitting dangerous CO₂ levels, some industries have an elevated risk.

Beverage operations routinely see 5,000-30,000 ppm in cellars and coolers – that morning inventory check isn’t just cold, it could be deadly if a fitting leaked overnight. Your average brewery cellar runs 10,000 ppm during active fermentation. Add a faulty ventilation fan and you’re at 30,000 ppm before anyone notices. Those CO₂ lines running to your draft system? Every fitting, every valve, every connection is a potential leak point adding to ambient levels.

Labs and research facilities hit 50,000-100,000 ppm when they’re running experiments with dry ice or using CO₂ as a carrier gas. One knocked-over dewar in a small lab? You’ve got seconds to get out, not minutes.

Fire suppression testing facilities deliberately flood spaces with 100% CO₂ (1,000,000 ppm). Their techs need to know the danger.

But it’s not just these obvious high-risk facilities. Fast-food workers changing soda fountain cylinders, greenhouse operators enriching for plant growth, welders using CO₂ shielding gas – one stuck valve or failed regulator puts them in the same danger zone as that brewery cellar.

In general, you’re more likely to hit dangerous CO₂ levels if you store CO₂ in bulk, use it in confined spaces, or both.  

How Do You Stay Safe?

Keep it simple: know the thresholds that matter – 5,000 ppm (get fresh air), 15,000 ppm (get out soon), 30,000 ppm (get out now).

When the alarm is triggered at 5,000 ppm, that’s not a suggestion. Open doors, check ventilation, and find the source. Don’t wait for the headache to confirm what the monitor’s already telling you.

At 15,000 ppm, you experience strong symptoms if you don’t get out soon. Your body’s already working overtime trying to cope, and that confusion creeping in? It only gets worse.

Hit 30,000 ppm and you immediately evacuate. No grabbing tools, no quick valve checks, no being a hero. The distance between 30,000 ppm and unconscious is shorter than you might think at that moment.

The “tough it out” mentality can result in death. CO₂ doesn’t care about your deadline or your shift schedule.

Make 5,000 ppm your operational red line – not only because regulations say so, but also because staying well below it means never finding out what 30,000 ppm feels like.

Lawrence Haynes

Currently serving as Marketing Director at WestAir Gases & Equipment in San Diego, CA Lawrence leverages his expertise in industrial gas solutions and equipment marketing. With a proven track record in cross-industry marketing strategy, he brings a specialized experience in content development, marketing automation, and partner relations to the industrial gas sector.