When did carbon dioxide gas chambers start coming into use?

• In 1999, carbon dioxide was used to stun 2% of all pigs and 2.2% of pigs in establishments that slaughtered more than 4,500 pigs per day.

• By 2020, those numbers had risen to 86.2 % and 96.2%, respectively.

• Today, according to FSIS enforcement records, at least 32 slaughter plants use CO2 gas slaughter systems.

• 113.5 million of the 131 million pigs we slaughter every year in the United States are killed in carbon dioxide gas chambers.

What do the animals experience?

• High concentrations of carbon dioxide do not cause immediate unconsciousness, so they may experience respiratory distress, hyperventilation, a sense of breathlessness or “air hunger,” severe anxiety, gasping, suffocation, and pain due to irritation of the mucus membranes, muscular excitation, fear, panic, and stress.

What factors can change the pig’s welfare in the gas chambers?

• The concentration of carbon dioxide gas can fluctuate based on environmental conditions such as wind, temperature, and humidity, as well as patterns of opening and closing the doors. Lower carbon dioxide concentrations may mean the animals take longer to become unconscious and may regain consciousness during sticking or bleeding.

• Low temperature or humidity of carbon dioxide is too low, it can cause burns on the skin and pain on inhalation.

• The speed at which the gondola descends into the pit.

• Sex, age, pulmonary disease, and genetics can also affect how rapidly pigs lose consciousness.

• Improper handling and use of electric prods can also result in a longer time before gaining unconsciousness.

• High sound levels, from the screams of other pigs or the machine can increase excitement or distress.

What are the mechanisms by which discomfort or excitement are caused?

• Pain due to carbonic acid formation on the respiratory or ocular membranes.

• Production of “air hunger” or feeling of breathlessness.

• Direct stimulation of ion channels within the amygdala is associated with the fear response.

  • The European Food Safety Authority

What are the different types of gas chambers?

• The dip-lift system lowers pigs directly into the maximum concentrations of carbon dioxide.

• The paternoster (Ferris wheel-like) system has multiple gondolas that rotate more erratically with stops at various points for loading and unloading pigs.

What are the alternatives to carbon dioxide gas chambers?

More detail about alternatives is available in this review article. Most of the information for the summary below was taken from this article.

Sindhøj E, Lindahl C, Bark L. Review: Potential alternatives to high-concentration carbon dioxide stunning of pigs at slaughter. Animal. 2021 Mar;15(3):100164.

Gas Alternatives

• Inert gases do not react with other substances, do not irritate the mucous membranes, and are free from smell, color, or taste. They work by creating an environment with <2% oxygen. Hypoxia itself does not cause suffering; it's the sensation of carbon dioxide building up that causes the “air hunger” and painful sensation.

• In one study, pigs did enter a chamber with 90% argon with no signs of aversion. Other studies showed improved welfare, but one study did show some aversion. Argon is more dense than air, so it works well in the pits. Some studies showed longer duration of convulsions and longer time to loss of posture. They would need to be exposed to the environment for 7 minutes before the majority of pigs would die. To shorten the process, there could be a two-step process involving argon and then carbon dioxide.

• Nitrogen is another option that makes up 78% of our atmosphere. The problem is that it is less dense than air, so it would rise up out of the pits, and since our atmosphere already contains high concentrations of nitrogen, getting concentrations even higher is challenging. There are some studies with nitrogen and carbon dioxide that show reduced discomfort. Additionally, high-expansion nitrogen foam also helps keep it from mixing with air. But, aversive behaviors were seen in 67% of pigs. Another study showed that pigs did not show strong aversive behaviors.

• Helium is another option, but it is also less dense than air. A dome can be placed over the pit. No aversive behaviors were seen in pigs stunned with helium. The time to loss of posture was only 20 seconds, and only 180 seconds of exposure was needed to ensure unconsciousness through bleeding.

• Xenon is another option and is more dense than air, but it is so rare that it is unfeasible.

• Carbon monoxide is another option, but there are concerns for the human worker’s safety. When carbon monoxide was combined with nitrous oxide, there was no excitation seen.

• Nitrous oxide alone is another option, or a two-step process involving nitrous oxide than carbon dioxide.

Physical Methods

Electrocution

• In head-only stunning, animals can regain consciousness in 30 seconds, so they have to be bled within 15 seconds. In the head-to-heart method, proper placement of the electrodes is important, and poor placement can cause pigs pain. A restrainer can help with placement, but the restrainer itself can be aversive. Additionally, getting them to line up single-file sometimes requires the use of electric prods, which causes them pain.

Electromagnetic radiation

• This has not been studied in pigs and requires restraint of their head. This induces an increase in temperature in the brain. In cows, there were no behavioral expressions of distress. There might be a way to make it work for group stunning in the future.

Single-pulse ultra-high current

• A handheld single-point device is an alternative to electrical stunning but has not been studied in pigs. It has a longer stunning effect and decreases to no epileptic seizures. It requires close proximity to the handlers, which may cause stress in the pigs.

Stop pig slaughter

• Are we trying to solve a problem that shouldn’t exist in the first place? Doesn’t everyone deserve the choice to eat the food they want without having to harm animals? Instead of investing in new killing technology, we could invest in increasing access to affordable, nutritious food that doesn’t harm anyone.

Do other countries require the use of video cameras to monitor gas chamber stunning?

• Yes.

  • Spain requires systems that “cover the facilities in which live animals are found, including unloading areas, driving aisles, and areas where stunning and bleeding to death activities are carried out . . . .” including “areas that are difficult for staff to access, including confined spaces, [and] installations that make up the stunning system . . . .”

  • England and Scotland require:

    • “a complete and clear image of killing and related operations in all areas of the slaughterhouse where live animals are present,” including “in areas where it is difficult for inspectors to access, for example, in cramped killing areas and gas stunning systems.”

  • Israel

    • Video footage is transmitted live to a central control room at the Ministry of Agriculture’s Veterinary Services. Facilities are required to install cameras that film at all times and in every area where animals are

      handled up to their slaughter.

What does the international community say about gas chambers?

• The European Food Safety Authority (EFSA)

  • "Exposure to CO2 at high concentrations (defined in their opinion as higher than 80% by volume) is considered a serious welfare concern because it is highly aversive and causes pain, fear, and respiratory distress” and recommended replacing CO2 with less aversive gas mixtures.” 

• World Organization for Animal Health

  • “[i]t should be possible to inspect the CO2 chamber whilst it is in use . . .” .”

What are the effects on slaughterhouse workers?

• Gas chambers separate workers from the killing. Indeed, it is the only method in which killing is not directly observed. This may result in better worker retention and less psychological harm to workers than methods in which the worker is more directly involved with the killing. However, that has not been well described in the scientific literature, only in a historical context. One can observe from one clip that the worker may be suffering from psychological distress just from the task of pushing pigs into the chamber, as he is doing it carelessly, hitting the pigs needlessly, closing the door on one's head, and spraying them with a hose.

• In order to ensure compliance with federal law and the correct operation of the machines, the killing must be directly observed.

• The veterinarians who observed this footage in order to draft the statement suffered secondary traumatic effects, even after just a few minutes of watching. These effects include intrusive thoughts, irritability/agitation, emotional outbursts, mood swings, and nightmares. There should be a concern for the psychological well-being of anyone tasked with performing this job.
  

• Studies show slaughterhouse workers face high rates of post-traumatic stress disorder and perpetration-induced traumatic stress, as well as anxiety and increased feelings of aggression when working on the kill floor. They often feel a need to disassociate and, as a result, face high levels of drug abuse and addiction, as well as violent and sexual crimes.

• Witnessing death, threatened death, or serious injury is considered “trauma,” according to the Diagnostic and Statistical Manual of Mental Disorders.

• Those who perform the work of killing in their jobs suffer from perpetration-induced traumatic stress. Dr. Rachel MacNair describes in an April 2023 article in the American Medical Association Journal of Ethics how slaughterhouse workers suffer from nightmares, detachment, or emotional numbness that might lead them to commit other forms of violence. This is known as “spillover,” and a 2009 study showed that slaughterhouse workers had increased rates of arrests for violent crime and rape, ultimately affecting the larger community.

• The children of slaughterhouse workers may be impacted as well. For children, witnessing or being a victim of violence or having a parent who suffers from mental illness represents an Adverse Childhood Experience (ACE). The accumulation of traumatic experiences throughout one's childhood can have future physical and mental health consequences. The CDC says, “The economic and social costs to families, communities, and society totals hundreds of billions of dollars each year.” By preventing ACEs, we would prevent 1.9 million cases of heart disease and 21 million cases of depression.

• If we knew a workplace was causing kidney disease, liver disease, or heart disease in a large number of their workers, we would take that very seriously, and those issues would be addressed with a sense of urgency. The brain is an organ that must be protected just as much, if not more, than the kidney, liver, and heart, but harms to this organ are often overlooked. The psychological and community impacts of workers performing the task of killing and witnessing death must be addressed.