I really would not rely on a Fire Chief for diagnostic skills. Especially one looking for fame, funding and publicity talking to the media. If it was CO poisoning, the hospital would easily measure raised carboxyhaemaglobin levels - simple blood test in a small hospital, putting a probe on a finger in a teaching centre.
Many things cause nausea, headache and dizziness. CO poisoning is rare and in most cases you would smell other contaminants. Anyhow, it appears engineering found no problem.