Beyond the Chart: Understanding the impact of carbon monoxide on the Human Body

For decades, carbon monoxide (CO) safety education has relied on a familiar visual: a chart linking parts per million (PPM) to predicted health effects. It’s neat, it’s easy to reference, and it’s dangerously incomplete.

Because carbon monoxide exposure doesn’t follow charts. It follows conditions: who you are, where you are, and how long you’re there.

That’s why it’s time for a new way to understand CO’s impact: a model that puts people, not numbers, at the center.

Introducing The CO Effect Model

The CO Effect Model is a modern way to understand how CO exposure really affects the body. Instead of a fixed list of symptoms, it looks at how three factors interact to shape every CO event:

1. Unique Biology

2. PPM Level (Air Concentration)

3. Amount of Time Exposed

Each factor alone is a risk. But when they overlap (when air concentrations rise, exposure lasts longer, and the person’s biology is more vulnerable), the effect intensifies.

"The CO Effect reminds us that carbon monoxide’s danger isn’t static. It’s shaped by who’s in the room, how the air moves, and how long it goes unnoticed,” says Nikki James Zellner, founder of CO Safe Schools and mother of school-based carbon monoxide poisoning survivors.

Factor 1: Unique Biology

Every individual's body processes oxygen and carbon monoxide differently. That means no two exposures are alike.

• Children and infants breathe faster, absorbing CO more quickly.

• Pregnant women transfer CO through the placenta, where fetal blood binds it even more tightly.

• Older adults or those with heart or lung conditions already have limited oxygen reserves.

• And healthy adults can be misled: mild headaches or dizziness are often mistaken for fatigue or illness.

“The same level of CO that makes one person dizzy could send another to the hospital,” says Zellner.

Factor 2: PPM Level (and Size of Space)

PPM (or parts per million) measures how concentrated CO is in the air of a particular space. But that concentration depends on the space itself.

A small, enclosed classroom or daycare will reach dangerous PPM levels much faster than a large gym or auditorium. Poor ventilation or faulty equipment only magnifies the risk.

“It’s like pouring dye into water, one drop changes a glass faster than it changes a pool,” Zellner says. "A small, one-room daycare in a historic building will certainly experience a different kind of CO event than a large auditorium."

Factor 3: Amount of Time

Time is carbon monoxide’s silent accomplice. Even low concentrations can become dangerous if exposure lasts long enough, just ask any person who has been chronically exposed to CO in their home or business.

CO binds tightly to hemoglobin, the molecule that carries oxygen in your blood. Once it’s attached, it takes hours (and sometimes medical intervention) to clear. That’s why a slow-building leak can be just as dangerous as a short burst of high PPM air.

"With CO, time is the hidden danger, because symptoms often appear only after serious harm to the body has begun,” says Zellner.

Why the Old Chart Falls Short

Traditional CO charts focus on PPM and time, two static variables that ignore the human and environmental context. They assume everyone reacts the same way, in the same space, under the same conditions.

Real life doesn’t work like that. Schools, dorms, daycares, buses, and gyms each present unique combinations of space, ventilation, and occupancy, and the people inside range from infants to retirees.

The CO Effect Model replaces the oversimplified “dose chart” with a realistic, human-centered framework for understanding risk.

Visualizing the CO Effect

The CO Effect Model is represented by three overlapping circles:

• Unique Biology

• PPM Level

• Amount of Time

Each circle alone represents a risk. Where they overlap, those risks multiply; and at the center lies the greatest health impact of carbon monoxide: when all three converge.

Why This Matters

Understanding CO risk through the CO Effect Model changes how we approach prevention.

• It highlights why CO detection must be standard in every school, daycare, and public building.

• It supports more personalized emergency response and medical treatment.

• And it reframes CO safety as part of a broader conversation about indoor air quality and occupant health.

  
  

Until CO safety becomes mainstream, we need to learn to protect ourselves and each other through awareness, detection, and education.

The Bottom Line Regarding the Impact of Carbon Monoxide on the Human Body

Carbon monoxide doesn’t discriminate, but it also doesn’t behave predictably. Its effects are shaped by the people it reaches, the spaces it fills, and the time it goes unnoticed.

By understanding the CO Effect Model, we replace confusion with clarity, and in doing so, move one step closer to ensuring every school, campus, and community breathes safe air.

Want to Learn More?

Download the CO Safety Check Toolkit to help you identify risks in your building.

[Download Here]