On January 25, 2024 the execution of Kenneth Eugene Smith took place in Alabama by nitrogen hypoxia. The execution was not recorded, so the evidence that Kenneth was seen "writhing and convulsing" relies entirely on the testimony of witnesses who attended the execution.
Under Alabama law (Code § 15-18-83), certain individuals from outside the prison service may be present at an execution, including members of the media and the families of both the victim and the condemned. As none of them were medical professionals, the observation likely refers to the non-pathological sense of the term “to shake violently” (OED):
- Ivana Hrynkiw (Media witnesses): "Smith visibly shook and writhed against the gurney for around two minutes. His arms thrashed against the restraints."
- Marty Roney (Media witnesses): "Smith convulsed for two minutes, with seven minutes of heavy breathing as he took large breaths."
- Rev. Jeff Hood (Spiritual advisor) "What we saw was minutes of someone struggling for their life"
- Mike Sennett (Family of victim): "With all that struggling and jerking and trying to get off that table, more or less, it’s just something I don’t ever want to see again."
- Deanna Smith (Relative of condemned): "Tonight, I watched my husband jerk and convulse and gasp for air for at least 10 minutes."
The Guardian article you referenced noted that the execution of Alan Eugene Miller, who was also executed by nitrogen hypoxia, involved "similar effects". Alabama Corrections Commissioner John Q. Hamm confirmed that both Kenneth Smith and Alan Miller exhibited "involuntary body movements" (The Associated Press, 27 September 2024)
Just like in Smith we talked about there is going to be involuntarily body movements as the body is depleted of oxygen. So that was nothing we did not expect,
The idea that the execution of Anthony Todd Boyd also faced "similar effects" wasn't mentioned, but a media witness of the execution noted sudden body movements (Montgomery Advertiser, 24 October 2025):
The gas apparently began flowing, as Boyd's lower half of his body began to jolt. Boyd shifted, rolling to his side for a few seconds, with his body angled toward the viewing chamber. He appeared to tremble and shudder.
As you correctly pointed out, this seems counter to the Wikipedia article on inert gas asphyxiation
that quoted a 2003 Safety Bulletin from The U.S. Chemical Safety and Hazard Investigation Board (USCSB, June 2003, pg. 2):
Breathing an oxygen-deficient atmosphere can have serious and immediate effects, including unconsciousness after only one or two breaths. The exposed person has no warning and cannot sense that the oxygen level is too low.
None of those claims are cited, but the idea that unconsciousness occurs after "only one or two breaths" is not what has been observed. In 1963, medical researcher, John Ernsting, studied the effects of breathing in nitrogen and published the results in The Journal of Physiology (1963, pg. 293):
In the few experiments in which nitrogen was breathed for 17-20 sec unconsciousness supervened and was accompanied on most occasions by a generalized convulsion.
In an editorial article published in the journal of Experimental Physiology, researchers estimated this would be around "four or five breaths" but is highly dependent on physiology (David C. Poole et al., 29 March 2024)
Moreover, at a normal breathing frequency of ∼15 breaths/min, the 17–20 s elapsed before Ernsting's subjects lost consciousness allows for at least four or five breaths, and far more if the subject is hyperpnoeic and hyperventilating owing to nervousness and the carotid body response to the falling arterial 𝑃O2.
The statement that an "exposed person has no warning and cannot sense that the oxygen level is too low" likely refers to the table titled "Effects of Oxygen Deficiency on the Human Body", which originates from a 2001 Safety Bulletin issued by the Compressed Gas Association.
The table shows that once oxygen concentration drops below 19% then the "unnoticeable adverse physiological effects" become very much noticeable (USCSB, June 2003, pg. 3):
| Atmospheric Oxygen Concentration (%) |
Possible Results |
| 20.9 |
Normal |
| 19.0 |
Some unnoticeable adverse physiological effects |
| 16.0 |
Increased pulse and breathing rate, impaired thinking and attention, reduced coordination |
| 14.0 |
Abnormal fatigue upon exertion, emotional upset, faulty coordination, poor judgment |
| 12.5 |
Very poor judgment and coordination, impaired respiration that may cause permanent heart damage, nausea, and vomiting |
| <10 |
Inability to move, loss of consciousness, convulsions, death |
It should be noted that in the updated 2014 Safety Bulletin, the reported effects of oxygen concentrations below 10% were revised to state that between 10% and 6% there is “perhaps unconsciousness” followed by “convulsions, then cessation of breathing, followed by cardiac standstill (death)” at levels below 6%.
In Kenneth Smith’s case, his reported attempt to hold his breath may have been influenced by the effects of "emotional upset" and "poor judgment" which, when combined with "impaired respiration" and "faulty coordination" could produce sudden movements of discomfort that observers described as "convulsing".
In summary, it's unclear whether the sudden movements are due to the natural onset of convulsions, where the person may or may not be conscious, or the acts of "faulty coordination" by someone trying to breathe due to "impaired respiration".
