Suicide by Inhalation of Carbon Monoxide Produced by Mixing Formic Acid and Sulfuric Acid

Carbon monoxide (CO) is a common agent of intentional poisoning due to its accessibility and perceived painless lethality. While most CO suicides result from combustion sources, the combination of formic and sulfuric acid represents a lesser-known but increasingly utilized method of CO generation through chemical reaction. This report describes the case of a 23-year-old male who died by CO inhalation inside a closed vehicle after mixing these 2 acids. The scene investigation revealed chemical containers and a suicide note; toxicological analysis showed 90% carboxyhemoglobin saturation and the presence of formic acid. An external examination noted cherry-red lividity and foam at the mouth. This case highlights a rare but growing method of suicide, as supported by a review of the literature identifying 17 fatal and 5 nonfatal cases. Reported carboxyhemoglobin levels ranged from 15.1% to 93.4%, with most decedents being young males. Acid vapors caused mucosal and dermal injuries in multiple cases, posing risks to bystanders and first responders. This report emphasizes the need for awareness of this emerging suicide method, recognition of its chemical hazards, and the implementation of appropriate safety protocols during scene investigation and forensic evaluation.