Have any jurisdictions historically used carbon monoxide for executions and what were the outcomes?
Executive summary
Carbon monoxide has been used historically as an execution and mass-killing agent in multiple jurisdictions — from ancient reports of Greek and Roman practice to 20th‑century gas chambers and mobile "gas vans" in Nazi Germany — and in state-run U.S. gas chambers where poisonous gases including carbon monoxide and hydrogen cyanide were employed; those uses resulted in death but also in lasting controversy, legal challenges, and eventual near‑abandonment of the method [1] [2] [3]. Contemporary debate resurfaces periodically — for example advocates of carbon monoxide as a supposedly “painless” replacement for lethal injection — but past outcomes, technical risks, moral stigma and legal challenges have limited its modern adoption [4] [5].
1. Historic uses and documented outcomes: ancient to modern
Accounts compiled by medical and historical sources trace use of carbon monoxide and other asphyxiants to ancient times and to industrial‑scale killings in the 20th century: classical sources and later historians record the Greeks and Romans using poisonous vapors for execution, and Nazi programs in the 1940s established gas chambers and gas vans that used bottled carbon monoxide and engine exhaust to kill large numbers of people — outcomes that were lethally effective but criminal and genocidal [1] [2]. In the United States, gas chambers became a state execution option in the 20th century; states adopted lethal gas (variously hydrogen cyanide or carbon monoxide among other agents) as an alternative to hanging and shooting, and at least eleven men were executed by gassing in several states after 1977, producing certain deaths but also sustained legal and ethical backlash [3] [2].
2. Technical and practical outcomes: effectiveness, complications, and risks
Where carbon monoxide has been used the physiological outcome — binding to hemoglobin and producing hypoxic death — is well established and lethal; Claude Bernard’s 19th‑century physiology helped explain the mechanism [1]. Yet practical problems have surfaced repeatedly: risks of gas leakage that could endanger bystanders or staff, difficulty guaranteeing a quick, painless death in every case, and the operational complexity of containing an odorless, colorless gas have all been cited historically as reasons for caution or abandonment [5] [2]. Those operational and safety concerns helped push many jurisdictions away from gas methods toward alternatives like lethal injection or, more recently, proposals for inert‑gas hypoxia using nitrogen [3] [6].
3. Legal, moral and reputational outcomes: stigma and litigation
Use of toxic gases for execution has produced disproportionate legal challenge and reputational harm: gas chambers and gas vans are central to the evidence of crimes against humanity in Nazi atrocities, creating a powerful moral stigma that influences modern policy choices and public opinion [2]. In the U.S., gas execution’s record of controversy — court fights over whether gassing is “cruel and unusual,” coupled with botched or contested executions — has driven litigation and legislative shifts; some states still retain gas methods on the books but use them rarely or not at all because of legal and political pushback [3] [5].
4. Revival attempts and competing narratives about humaneness
Advocates occasionally resurface carbon monoxide as an alternative — for instance, proponents linked to assisted‑suicide practitioner Jack Kevorkian claim carbon monoxide can produce a “painless” death and have lobbied authorities to consider it as a substitute for troubled lethal injections — but such claims meet counterarguments about stigma, safety, and potential for error, and so far have not produced institutional adoption for state executions [4]. At the same time, recent legislative moves to authorize nitrogen hypoxia in some U.S. states reflect a continuing search for methods perceived as more “humane” than older techniques, even as scholars and advocates warn about untested risks [6] [7].
5. Bottom line: used historically, lethal but controversial; modern use effectively shelved
The historical record is clear that carbon monoxide and similar gases have been used as execution methods and for mass killing and that the outcome is death when administered in lethal concentrations; however, those uses generated severe ethical condemnation, operational hazards, and legal challenges that have largely removed carbon monoxide from modern official execution practice in democratic jurisdictions, even as isolated proponents argue for reconsideration [2] [3] [4]. Reporting and scholarship document effectiveness in producing death but also show why reputational, safety and legal factors have kept carbon monoxide out of mainstream modern execution protocols [5] [1].