🧪 Carboxyhemoglobin (COHb) Concentration Calculator Simulator

Carbon Monoxide Enters Ambient Air

A colorless, odorless gas begins displacing oxygen in breathed air.

• Combustion: CO Source (incomplete burning)
• 0%: Detectability (no smell, no color)
• 400–1000 ppm: Typical fire scene (ambient CO)
• 50 ppm: OSHA 8-hr limit (occupational ceiling)

Why CO is undetectable

No smell, taste, or color warns of rising CO.

Common exposure settings

Fires, faulty furnaces, and closed-garage engines.

Ambient ppm is the starting input for every COHb calculation.

Forensic relevance

Scene ppm anchors the reconstructed exposure timeline.

CO Competes With Oxygen for Hemoglobin

Carbon monoxide binds hemoglobin roughly 240 times tighter than oxygen.

• ~240×: Affinity ratio (M) (CO vs O₂ for Hb)
• 4: Hb binding sites (per tetramer)
• Fast: O₂ unbind rate (seconds-scale)
• Very slow: CO unbind rate (hours-scale)

Haldane affinity constant

CO displaces O₂ far faster than O₂ displaces CO.

Site-by-site displacement

Each of four heme sites can independently trap CO.

Higher ambient ppm raises the odds any given collision binds CO.

Why symptoms lag exposure

Binding is essentially one-directional once CO locks on.

Carboxyhemoglobin Percentage Accumulates

Bound CO sites accumulate toward an exposure-dependent equilibrium level.

• τ≈4h: Equilibration constant (model half-life)
• Saturating: Rise pattern (exponential approach)
• 2: Governing variables (ppm and hours)
• <3%: Baseline (nonsmoker) (normal COHb)

Exponential approach to equilibrium

%COHb climbs fast at first, then levels off over time.

Equilibrium ceiling

Ambient ppm sets the maximum reachable %COHb.

The gauge fill mirrors accumulated bound-CO fraction.

Duration matters as much as concentration

Short high-ppm and long low-ppm exposures can converge.

Concentration-Time %COHb Calculation

A saturation formula converts ppm and exposure hours into %COHb.

• Haldane-based: Model type (saturation curve)
• ppm, hours: Inputs (two sliders)
• %COHb: Output (single value)
• Forensic estimate: Use case (not clinical dosing)

Equilibrium term

COHb_eq scales ppm through the 240× affinity constant.

Time term

A 1−e^(−t/τ) factor scales the approach to equilibrium.

Investigators back-solve exposure time from a measured COHb.

Model limits

Ventilation rate and activity level shift real results.

Interpreting COHb Against Forensic Thresholds

Computed %COHb is classified against incapacitating and lethal bands.

• 30–40%: Incapacitating range (confusion, syncope)
• 50–70%: Lethal range (coma, death)
• 5–10%: Smoker baseline (chronic elevation)
• >50%: Fire-death median (reported autopsy COHb)

Threshold bands

Fixed COHb ranges separate mild from lethal outcomes.

Autopsy interpretation

Postmortem COHb helps confirm death by CO poisoning.

COHb over ~50% is generally considered a lethal finding.

Confounders

Preexisting disease can lower the lethal threshold further.