Near Miss: Post-Fire Metering for Carbon Monoxide

Miami-Dade Fire Rescue companies fought a fire in a first-floor apartment of a four-unit apartment building at approximately 0300. The building had two apartments on the first floor and two on the second floor. Approximately two hours after the fire was declared under control occupants of the unit directly above the fire asked firefighters, who were performing overhaul, if they could return to their apartment which was perfectly clear of smoke and smoke odor.

An experienced veteran Captain gave them permission to reoccupy their apartment. A few minutes passed and it occurred to the Captain that he had made a big mistake; he forgot to check their apartment for Carbon Monoxide (CO). He should have known better because over his career he had responded to several fires where units distant from a fire were perfectly clear and still had dangerously high levels of CO. Realizing his mistake, he requested a unit go back to the station to get the Battalion Chief’s CO meter. The meter measured 130 parts per million (PPM) of CO in the second-floor apartment.

Carbon Monoxide (CO) Facts
Almost every fire in a building produces an abundance of CO because almost every fire in a building involves a large fuel load of plastics; synthetic petrochemical based materials such as polyethylene, polystyrene, polyvinyl chloride, and polyurethane foam.

Firefighters understand that burning plastics produce twice as many British Thermal Units (BTUs) per pound than naturally occurring materials, such as wood, but they may not grasp the concept of heat release rate (HHR); that is, the speed at which heat energy is released from burning fuels. It requires oxygen for burning fuels to produce heat energy. Materials that burn with an increased HRR require more oxygen than materials with lower HHRs. Because plastics have such a high HRR, they burn with a voracious appetite for oxygen and can rapidly consume the oxygen available inside a closed building and become ventilated limited. Fires in a ventilation limited/oxygen deficient conditions burn incompletely; hence, they produce CO.

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The heat energy produced from a fire creates pressure that forces smoke and fire gases such as CO out of a building or, in the case of multiple dwellings or rows of stores, into other units. At first, the CO heated by a fire is buoyant and will rise to upper levels, such as apartments above a fire or in an attic or cockloft where it can spread over multiple occupancies and then, as it cools, it sinks to lower levels.

Consider these examples where high levels of CO were found in occupancies distant from the fire:

• Firefighters quickly bring an apartment fire under control. The fire apartment is in the East end of a multiple unit apartment building. A few days later family members of an elderly women who lives in the West end of the building, hundreds of feet away from where the fire occurred, become concerned because they hadn’t heard from her and find her deceased. The medical examiner determined that she died from CO poisoning. It is believed that wind pushed the CO that had accumulated in a common attic from the East end of the building to the West end, once it cooled and lost buoyancy, it sank into the woman’s apartment.
• A fire in a second-floor apartment produced dangerously high levels of CO in several apartments on the first floor.
• Firefighters examining stores and offices in a strip shopping center found over 100 PPM of CO in businesses hundreds of feet from the fire occupancy in a building with no common attic.

Lesson Learned:
Remember that CO is odorless, colorless, and tasteless; hence it can accumulate in occupancies above, below, and at great distances from a fire that are perfectly clear of smoke and the odor of smoke.

• Do not underestimate how CO can find its way into occupancies that are separated by substantial walls and floors. Consider that CO can migrate to electric meter rooms, accumulate at the top and bottoms of stairwells, and elevator shafts. Similarly, CO can leak from poorly fitting trash chute doors and contaminate several floors.
• Realize that a call for people with headaches, dizziness, nausea, or vomiting in a building where there had been a fire hours before, may not be a coincidence, they could be suffering from the effects of CO produced by the fire.
• Once a fire is out, it is the fire department’s responsibility to determine when it is safe for occupants to return to their building. The fire department cannot make this determination without thoroughly metering the building for CO.

BILL GUSTIN is a 44-year veteran of the fire service and a captain with Miami-Dade (FL) Fire Rescue. He began his fire service career in the Chicago area and is a lead instructor in his department’s Officer Development Program. He teaches tactics and company officer training programs throughout North America. He is a technical editor of Fire Engineering and an advisory board member of FDIC International.