Documented Dangers of Gas Chambers and Carbon Monoxide Poisoning

by on September 5, 2011

Four state and local agencies of North Carolina government have documented hazards of faulty gas chambers and supply cylinders at public animal shelters since 2004. Leaks and malfunctions were recorded by the North Carolina Department of Labor, North Carolina Department of Health and Human Services, North Carolina Department of Agriculture, and local fire marshals in Reidsville and Stokes County. The findings of these agencies were obtained through public record requests.

Most gas chambers in our state had reportedly never been formally inspected prior to 2004. Since that time, complaints from thousands of residents to government officials and the media have brought the controversial euthanasia method to the forefront.

One of the most compelling documents is a North Carolina Department of Labor inspection for Sampson County Animal Control in 2004 (1). The inspector’s worksheet reads,

“The animal begins to struggle because it cannot breathe…They wait approximately 10 minutes until the animal stops making sounds and then turn on a fan that is supposed to evacuate the CO from the chamber.”

Gas monitor readings showed employee overexposure to carbon monoxide, which the officer believed “is occurring when the chamber door is opened to remove the animal.” No respiratory protection was provided for employees.

Reidsville Fire Marshal John Harris inspected a gas chamber at Rockingham County Animal Control in 2004, on the property of Reidsville Veterinary Hospital, after repeated attempts to repair gas leaks (2). An inspection from August 2004 recounts:

“Harris checked the chamber finding that the door seals to the chamber were in disrepair and damaged in several locations. Harris also observed where attempts to repair the seals were made with what appeared to be caulking. Also noted that the integral safety systems for monitoring carbon monoxide levels has been DISABLED. Vent pipe from the top portion of the chamber is poorly fitted and sealed with what appears to be adhesive tape. During operation of the euthanasia chamber carbon monoxide monitors were used to test levels present adjacent to the chamber….carbon monoxide levels exceeded 984 ppm in the area of the chamber….After the purge cycle during removal of animals a reading of 460 ppm still remaining in the chamber as officers removed dead animals.”

Not only can gas chambers leak and malfunction, but gas cylinders provided by carbon monoxide suppliers have also been documented as a potential hazard. North Carolina Department of Labor inspections revealed faulty gas cylinders at Columbus County Animal Control (3) and Davidson County Animal Control in 2006 (4). The Davidson County inspection notes that National Welders Supply does not formally test the cylinders for leaks. The Columbus County inspection says, “It was determined the overexposure occurred whenever the valve on the CO cylinder was initially opened, so the feasible engineering control would be to have the cylinder and valves checked for leaks.” Animal control supervisor Rossie Hayes replied to the NCDOL, asking “for any suggestion on how to check the unit for leaks.” He asked if employees should wear some type of respirator.

Stokes County Fire Marshal inspected a rusty dump-truck gas chamber at Stokes County Animal Control in January 2007 (5). A letter from the Marshal to shelter supervisor Sarah Shumate documented high levels of gas at the supply tank as well as the gas chamber door. Marshal Bradley Cheek warned:

“During the euthanasia process, levels of carbon monoxide in excess of 1000 ppm were detected on the exterior of the chamber loading door. It is not known what the exact readings were; this is due to the monitor having a maximum reading of 1000 ppm….Carbon monoxide is immediately dangerous to life and health at 1200 ppm.”

Yet another jaw-dropping inspection was performed for Montgomery County Animal Control by North Carolina Department of Agriculture inspector Shelly Swaim in 2007 (6). Swaim writes,

“It was reported to me by Mr. Beane that the chamber is leaking and that there were visible cracks as well as an insufficient gasket around door. There is also no mechanism to facilitate venting of this unit. Inmates were on property and addressing chamber issues at 12:17. It appears that this CO chamber even with corrections employed at this time will pose a significant risk to the safety and life of the operator.”

Industrial hygienist Marilyn Parker of the North Carolina Department of Health and Human Services has performed gas monitor readings for two animal shelters, Granville County Animal Control in 2006 (7) and Randolph County Animal Control in 2007 (8). Both inspections revealed high level leaks of carbon monoxide around the edges of the gas chamber doors. Chambers at both facilities are modern, commercially manufactured units. Concerning the Randolph County inspection, Parker wrote, “While the chambers were in operation the monitor was placed in various locations around the door seals. Levels of CO were detected in excess of 500 ppm around the door seal….It was determined that the seals did not prevent carbon monoxide (CO) from escaping while the chambers were in operation.” Ms. Parker requested in both letters that she be called for follow up inspections after corrections were made. As of October 2008, Parker said that she was not aware of any correspondence with county officials since the inspections.

CO levels above 10% are explosive, as affirmed by the gas chamber explosion at Iredell County Animal Control of Statesville in 2008. No inspection record for the machine was available, but an invoice shows that the unit had been purchased only months prior from Cutting Edge Fabrication, after originally being sold to Union County Animal Control in Monroe. In a Statesville News and Record article (9), Cutting Edge owner Stephen Whitesell is quoted: “Whitesell believes the fan somehow sparked the carbon monoxide before the gas could be purged from the chamber….Whitesell said the fan is not explosion proof.” To the contrary, the AVMA 2007 Guidelines on Euthanasia include this warning about carbon monoxide chambers, “Any electrical equipment exposed to CO (eg., lights and fans) must be explosion proof.”(10) Union County Sheriff Eddie Cathey told the Enquirer Journal in August 2008, (11) “the chamber that was eventually sold to Iredell was returned to Cutting Edge three years ago because it had a warped door.” These are among the most expensive and hi-tech gas chambers on the market. Gas chambers from this manufacturer are reportedly still in use at Gaston, Cabarrus, and Union county animal control facilities.

Dangers to Humans

Carbon monoxide oozing from gas chambers can put shelter workers at risk of health problems, some of which can be delayed for weeks after exposure.


*The AVMA 2007 Guidelines on Euthanasia warns humans operating CO chambers: “In humans, exposure to 0.32% CO and 0.45% CO for one hour will induce loss of consciousness and death, respectively. Carbon monoxide is extremely hazardous for personnel because it is highly toxic and difficult to detect. Chronic exposure to low concentrations of carbon monoxide may be a health hazard, especially with regard to cardiovascular disease and teratogenic effects.” (10)

* The National Institute for Environmental Safety and Health published an International Chemical Safety Card for Carbon Monoxide, which states,

“The gas mixes well with air, explosive mixtures are easily formed. The gas penetrates easily through walls and ceilings…Fatal if inhaled. May damage fertility or the unborn child if inhaled. Causes damage to blood if inhaled. Causes damage to blood and central nervous system through prolonged or repeated exposure if inhaled…Inhalation Risk: A harmful concentration of this gas in the air will be reached very quickly on loss of containment. Effects of Short-term Exposure: The substance may cause effects on the blood, resulting in carboxyhaemoglobinemia and cardiac disorders. Exposure at high levels may result in death. Effects of Long-term or Repeated Exposure: The substance may have effects on the cardiovascular system and central nervous system. May cause toxicity to human reproduction or development. ” (12)

* The U.S. Environmental Protection Agency says, “Perhaps the most insidious effect of CP poisoning is the development of delayed neuropsychiatric impairment within 2 – 28 days after poisoning and the slow resolution of neurobehavioral consequences.”(15)

* According to an article from the Journal of the American Medical Association in 2006, “Researchers discover a link between severe carbon monoxide poisoning and death years later from heart disease.”(14)

* A materials safety data sheet from National Welders Supply, a leading supplier of bottled carbon monoxide to animal shelters, says that carbon monoxide is “Harmful if inhaled. Causes damage to the following organs: Blood, Lungs, Cardiovascular System, Central Nervous System. Vapor may cause flash fire…Extremely flammable. Gas may accumulate in confined areas, travel considerable distance to source of ignition and flash back causing fire or explosion.” (18)

* A study by Ramona Hopkins and Fu Lye M. Woon states, “It is estimated that as high as 50% of individuals with carbon monoxide poisoning will develop neurologic, neurobehavioral, or cognitive sequelae.” (17)

* A study of patients poisoned by carbon monoxide, from LDS Hospital in Salt Lake City, Utah in 1999 concluded, “Ninety-three per cent of the patients exhibited a variety of cognitive impairments, including impaired attention, memory, executive function, and mental processing speed. Ninety-five per cent of the patients experienced affective changes including depression and anxiety.” (18)

* Yona Amatai studied the effects of low-level CO exposure on higher cognitive function. The study concluded, “The lower scores on neuropsychological tests indicate dysfunctions in memory, new learning ability, attention and concentration, tracking skills, visuomotor skills, abstract thinking, and visuospatial planing and processing. These dysfunctions correspond with previous reports of carbon monoxide neurotoxic effects in patients with moderate carbon monoxide poisoning. Low-level exposure to carbon monoxide results in impairment of higher cognitive functions.” (19)

* A 1925 study by William C. Stadie and Kirby Martin of Yale University School of Medicine says, “Occasionally the blood becomes free of carbon monoxide and the coma terminates, but the patient subsequently sinks into a coma again and dies, probably as a result of central nervous system damage.” (20)

* A 2006 study by Christopher Henry and Daniel Satran, M.D. states, “Myocardial injury is a frequent consequence of moderate to severe CO poisoning.” (21)

* The Department of Health and Human Services, Center for Disease Control and Prevention says, “Red blood cells pick up CO quicker than they pick up oxygen. If there is a lot of CO in the air, the body may replace oxygen in blood with CO. This blocks oxygen from getting into the body, which can damage tissues and result in death.” (22)

* Science Daily reported in 2004, “Brain damage occurs – days to weeks later – in half of the patients with a serious case of CO poisoning.” (23)

* A 1983 article from Archives of Neurology detailed delayed neurologic effects of CO: “The most frequent symptoms were mental deterioration, urinary or fecal incontinence, gait disturbance, and mutism.” (24)

* Dr. David G. Penney, author of several books on the subject of carbon monoxide, lists nervous system damage caused by CO exposure: causes seizure disorders, multiple-sclerosis-type disorders, speech impairments, forms of aphasia; effects on learning, decrements in intellectual capacity, judgment, ability to concentrate, memory, executive functioning, multi-tasking, emotion; effects on short- to long-term memory and limbic system, ataxia, and slurring of speech. (25)

Ineffectiveness of Gas Chambers

Several mishaps have been reported by North Carolina media, showing that gas chambers are not always effective. Leaking carbon monoxide can keep the machines from reaching or maintaining a lethal level of 6%-10% for animals inside the chamber. The result can be a slower death, or mere unconsciousness and assumed death before the animal is placed in a freezer, dumpster, landfill, or incinerator. Some animals do not die the first time, whether due to inadequate gas levels, age of animal, or health issues.

Kerry Prichard of the Charlotte Observer reported a leaking gas chamber at Cabarrus County Animal Control in March 1998. “The gas chamber used to euthanize the animals was in clear view of visitors and, some critics say, it didn’t always work well. Critics say it killed the animals too slowly or not at all, because of leaks or overcrowding….The gas chamber has been reconditioned and moved to the new shelter.” The same chamber is still in use, complete with patching compound. (26)

A September 2003 article from Charlotte Observer reporter Hannah Mitchell uncovered problems with a gas chamber used at Alexander County Animal Control. “League volunteers heard a dog barking in a freezer after it went through the shelter’s gas chamber and was assumed to be dead. The county’s gas chamber used for euthanizing animals is sealed with duct tape. Campbell worried that the makeshift sealer lengthened the time it takes for animals to die.” (27)

The Charlotte Observer’s “Death at the Pound” series in June 2003 reported the same problem in other county shelters : “In Union, as many as 10 dogs are gassed together in a 4-by-4-foot steel container. It replaced a cinder-block chamber that leaked, causing some animals to survive the gassing.” In the same article, Stanly County Animal Control Officer Randy Palmer described a situation with a newer commercially manufactured gas chamber: “After you bring them out, some of them aren’t all down. Sometimes we have to put them back in.” (28)

Heather Howard of the Charlotte Observer interviewed Catawba County officials in 2004. County Manager Tom Lundy said that the existing gas chamber at the animal shelter “is inefficient and outdated.” Emergency Services Director David Weldon felt that a new model “would ensure that animals in the device are euthanized.” (29) Instead, the county made the change to euthanasia by injection in 2008.

Doug Clark of the Sampson Independent wrote a gripping story about a litter of puppies that survived the gas chamber at the local shelter in 2004 and were later adopted, only to die the next day. Attempting to dispel rumors of parvo in the facility, former employee Dianna Williford admitted, “We had tried to euthanize those puppies a half hour earlier and it just didn’t work.”(30) The only method of euthanasia used by the shelter at that time was a carbon monoxide chamber.

The most well known canine gas chamber survivor in North Carolina is Davie, a dog who was found alive in a dumpster after being dumped and assumed dead by Davie County Animal Control of Mocksville in 2005. Local residents Jeff and Susan Armsworthy were discarding trash at the dump when they heard a whining noise, which turned out to be a crying puppy in a plastic bag in the dumpster. The fearless couple jumped in and rescued the pup among piles of animal carcasses. Author Mike Gunning wrote, “Apparently, one of the puppies, while knocked unconscious by the gas, didn’t inhale enough to be fatal. It appears to have become conscious while in the dumpster.” (31)

Though many shelters have made the transition toward humane euthanasia in recent years, at least 22 county animal control facilities in North Carolina still kill unclaimed animals in gas chambers as of December 2009.


1. North Carolina Department of Labor Inspection, Sampson County Animal Control, March 2004.
2. Reidsville Fire Marshal inspections of Reidsville Veterinary Hospital/ Rockingham County Animal Control 2004-2006.
3. North Carolina Department of Labor Inspection, Columbus County Animal Control, 2006.
4. North Carolina Department of Labor Inspection, Davidson County Animal Control, May 2006.
5. Letter from Stokes County Fire Marshal to animal control supervisor Sarah Shumate, January 4, 2007.
6. North Carolina Department of Agriculture, Montgomery County Animal Control, inspection by Shelley Swaim, September 19, 2007.
7. Letter from North Carolina Department of Health and Human Services, Epidemiology Section, Granville County Animal Control inspection, August 21, 2006.
8. Letter from North Carolina Department of Health and Human Services, Epidemiology Section, Randolph County Animal Control inspection, April 24, 2007.
9. Statesville News and Record, July 24, 2008, author Bethany Fuller.
10. 2007 American Veterinary Medical Association Guidelines on Euthanasia
11. Enquirer Journal article, August 3, 2008, Author Billy Ball.
12. National Institute for Environmental Safety and Health, International Chemical Safety Card, Carbon Monoxide.
13. “Heart Injury Due to Carbon Monoxide Poisoning Increases Long Term Risk of Death,” Journal of the American Medical Association, January 24, 2006, Timothy D. Henry, M.D.
14. “The Brain Lesion Responsible for Parkinsonism After Carbon Monoxide Poisoning,” Young H. Sohn, MD; Yong Jeong, MD; Hyun S. Kim, MD; Joo H. Im, MD; Jin-Soo Kim, MD, Archives of Neurology 2000;57:1214-1218. 
15. “Carbon Monoxide Poisoning- A Public Health Perspective,” US Environmental Protection Agency.
16. Carbon Monoxide Materials Safety Data Sheet, National Welders Supply. 
17. Neuroimaging, Cognitive, and Neurobehavioral Outcomes Following Carbon Monoxide Poisoning Ramona O. Hopkins, Fu Lye M. Woon, Brigham Young University
18. “MRI, quantitative MRI, SPECT, and neuropsychological findings following carbon monoxide poisoning,” Gale, S.D., Hopkins, R.O., Weaver, L.K., Bigler, E.D., Booth, E.J., Blatter, D.D., 1999, Brain Injury, 13 (4), pgs. 229-243.
19. “Neuropsychological Impairment From Acute Low-Level Exposure to Carbon Monoxide,” Yona Amitai, MD; Zoli Zlotogorski, PhD; Vered Golan-Katzav, MA; Anya Wexler, MD; Ditza Gross, PhD
Archives of Neurology. 1998;55:845-848.
20. “The Elimination of Carbon Monoxide from the Blood,” William Stadie and Kirby Martin, Yale University School of Medicine, 1925.
21. “Myocardial Injury and Long-term Mortality Following Moderate to Severe Carbon Monoxide Poisoning,” Journal of American Medical Association, 2006, Christopher R. Henry, BS; Daniel Satran, MD; Bruce Lindgren, MS; Cheryl Adkinson, MD; Caren I. Nicholson, RN; Timothy D. Henry, MD;295:398-402.
22. Department of Health and Human Services, Centers for Disease Control and Prevention,
23. “Long-term Effects Of Carbon Monoxide Poisoning Are An Autoimmune Reaction,” Science Daily; Veena M. Bhopale, Donald Fisher, Jie Zhang, and Phyllis Gimotty.
24. “Delayed neurologic sequelae in carbon monoxide intoxication,” Archives of Neurology, July 1983, I. S. Choi.
25. “Major Sites of Nervous System Damage,” Dr. David G. Penney.
26. “Happy Endings Now Possible for Strays,” Charlotte Observer, March 5, 1998, Author Kerry Prichard.
27. “Animal League Told to Leave- Alexander County Resumes Control of Shelter,” Charlotte Observer, September 7, 2003, Author Hannah Mitchell.
28. “Death at the Pound: Animals in the Charlotte Region…” Charlotte Observer, June 29, 2003, Authors Michelle Crouch and Scott Dodd.
29. “Needs of Animal Shelter Outlined- Catawba Official Pitches Plan,” Charlotte Observer, April 28, 2004, Author Heather Howard.
30. “Inhumane Treatment Or a Doing Their Best?” The Sampson Independent, February 07, 2004, Author Doug Clark.
31.”Puppy Survives Euthanasia Attempt, Trip to Dump,” Davie County Enterprise Record, April 2005, Author Mike Gunning.

Electronic copies of public records referenced above are available from the author at no charge.

Michele King is a board member of the North Carolina Coalition for Humane Euthanasia Members of this organization advocate for an end to gas chambers and other inhumane killing in animal shelters.

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