School CO Sources: The Five Main Ways Carbon Monoxide Builds Up In Daycares, K-12, and College Campuses
- Nikki James Zellner
- 3 hours ago
- 4 min read
When a carbon monoxide (CO) incident happens on a school campus, one of the first questions everyone asks is: “Where did it come from?”
Parents want to know. Staff want to know. Journalists want to know. Fire marshals and investigators need to know.
But right now, the language we use to describe CO sources in schools is inconsistent and confusing. News stories call it a “gas leak,” a “ventilation problem,” an “equipment issue,” or simply “fumes,” even when the actual hazard is carbon monoxide, a colorless, odorless gas created by incomplete combustion.
The result? The public gets confused, prevention gets harder, and incident data becomes unreliable.
To fix this, CO Safe Schools is establishing a set of plain-language, standardized CO source categories that can be used in school reports, media releases, research databases, and public communication. These categories make it easier to understand what happened, why it happened, and how to prevent it from happening again.
Below is a simple explanation of each category, written so anyone can follow.
Why We Need Standardized CO Source Categories
When schools, reporters, or emergency services use vague terms like “odor,” “gas issue,” or “mechanical problem,” or "HVAC issue," we lose critical clarity:
Was a combustion appliance malfunctioning?
Was it a ventilation failure?
Was it portable equipment or a vehicle?
Was there a fire?
Was it preventable?
Was it a human error?
Knowing the category helps identify not only the cause, but also the correct safety measures. What prevents a boiler malfunction is different from what prevents exhaust from a landscaping crew, or a blocked vent, or an idling bus.
Standardized categories make communication faster, clearer, and safer.
The Five Plain-Language School CO Source Categories
Below are the categories as they will appear in the CO Safe Schools Incident Database, along with simple explanations anyone can understand.
1. Mechanical – Stationary (Combustion Appliances or Heat Sources)
What this means: A built-in, non-movable system that burns fuel has malfunctioned, producing carbon monoxide.
These are the big, permanent systems that many people never think about but rely on every day.
Common examples include:
Boilers
Furnaces
Hot water heaters
Commercial-grade ovens or cooking equipment
Large generators
HVAC units with combustion components
Why this matters: These appliances run regularly, often in rooms no one enters. A failure can push CO into classrooms, cafeterias, hallways, or entire wings of a school. Most school CO incidents in the U.S. fall into this category.
2. Mechanical – Portable (Small Engines & Fuel-Powered Tools)
What this means: A movable device or tool with a gas-powered engine was used indoors or near the building and created dangerous levels of CO.
Examples:
Landscaping equipment (leaf blowers, snow blowers)
Floor buffers or cleaning machines
Construction tools (cutters, saws)
Portable gas-powered generators
Propane heaters
Maintenance tools with small engines
Why this matters: Many campus-based CO events happen during renovations, maintenance work, or routine cleaning, often when someone brings fuel-powered equipment indoors “just for a minute.” But that minute is all it takes.
Portable equipment = portable CO risk.
3. Ventilation Issue (Improper or Inadequate Ventilation)
What this means: The equipment might not be broken, but the air flow is. CO builds up when fresh air can’t enter, or combustion gases can’t exit.
This can be caused by:
A blocked or disconnected vent
A closed flue
A damaged or collapsed duct
An exhaust pipe clogged by debris, snow, animals, or nests
Incorrectly modified ventilation after renovations
Human error (operating indoors, valves closed, or dampers shut)
Why this matters: Ventilation failures turn otherwise safe equipment into CO hazards. These incidents often go unnoticed until people become sick.
This category is one of the hardest to diagnose and one of the easiest to prevent with more frequent inspection.
4. Vehicular (Cars, Buses, Trucks, or Heavy Equipment)
What this means: A vehicle or drivable machine was producing exhaust close enough to a school or occupied space that CO entered the building.
Examples:
Idling school buses
Delivery trucks
Parent pickup lines
Maintenance carts or utility vehicles
Forklifts
Vans or cars left running near air intakes
Outdoor generators parked too close
Why this matters: Modern vehicles still produce CO, and if the exhaust is near open doors, windows, or vents, it can enter the building quickly. This is common at early childcare centers with short drop-off loops or campuses with indoor loading docks.
5. Environmental (Fire-Related CO Occurs within Breathing Space)
What this means: A fire (natural, intentional, or accidental) produced carbon monoxide that spread into an occupied area.
Examples:
Wildfire smoke reaching campus buildings
A structure fire on or near school property
A trash fire or dumpster fire
Fireplace malfunctions
Burned food events that produce CO in enclosed kitchens
Why this matters: In these cases, fire is the primary hazard, but CO often spreads before flames do. This category helps differentiate fire-related CO exposure from mechanical failures or ventilation issues.
CO Source Categories Provide Clarity and Understanding
By using clear, standardized source categories, we can finally talk about carbon monoxide incidents in schools with accuracy and consistency. When a CO event occurs, the “why” matters; not only for fixing the immediate hazard, but for preventing the next one. The categories above give parents, educators, safety professionals, journalists, and policymakers a common language.
Whether the cause is a malfunctioning boiler, a gas-powered leaf blower, a blocked vent, an idling school bus, or a nearby fire, the terminology should leave no ambiguity. When we describe the hazard clearly, we can diagnose it more quickly, communicate it more effectively, and stop repeating the same mistakes. Clear language leads to clearer understanding, and clearer understanding leads to safer schools.
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