Best practices for nuisance wildlife control operators in New York State

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Ch 5: Step three: Do it - Lethal techniques

Carbon dioxide chamber

The technique is fairly simple: the animal is placed in an enclosed space into which carbon dioxide gas is added at a controlled rate. When the animal breathes this gas, it quickly loses consciousness and then dies. The entire process takes about five minutes.

How does it work?

Carbon dioxide (CO₂) is a colorless, odorless gas. It's called an "inhalant agent" because the animal must breathe it in. CO₂ affects the nervous system, the lungs, and the heart.

Can I use CO₂ on any species?

Carbon dioxide chambers work well to humanely kill birds, rodents, and most small mammals. But you may encounter problems if you try this technique on animals that are old, very young (less than 2 weeks old), weak, or sick with a respiratory disease, because they're often resistant to the effects of carbon dioxide. If possible, choose another technique to humanely kill animals that breathe slowly (such as reptiles or amphibians) or are very good at holding their breath (such as beaver and diving birds). Under these circumstances, CO₂ might take too long to be considered a best practice.

Commercial carbon dioxide chambers are often made of metal and have windows for monitoring the animal, but the chamber can be made of many materials, such as plywood or plastic. Coolers, garbage cans, and other containers have been converted into chambers. The best chambers are clear or have windows so you can monitor the animal, and are also easy to clean and transport.

You may want to have several chambers of different sizes and designs, and a portable model. For example, bats can be more humanely killed in a small chamber that fills faster. A small, clear plastic container with two holes drilled into it (one for the tube feeding the gas, and a vent hole) would work well.

One NWCO has rigged a garbage container on wheels to serve as both an enclosed trap and carbon dioxide chamber. He sets a cage trap within the chamber, then, after capturing the animal, wheels the can to a place where he can safely and discreetly attach the carbon dioxide tank and kill the animal. This combination of a trap within the CO₂ chamber also offers a safety advantage, because there is no handling of the animal. Consider such an approach, especially when dealing with sick, rabies suspect, or highly aggressive animals.

There may be a market niche for those willing to provide on-site wildlife euthanasia services, especially in areas where other techniques that are generally accepted by the public, such as shooting, aren't legal or practical. With care, carbon dioxide chambers can be safely transported.

Equipment needed

Homemade CO2 chamber

Many commercial coolers come with a drain hole at the bottom. Attach the hose to the drain hole. If your model lacks a drain hole, you can drill it out. To add a window to your chamber, drill through the cooler using a jigsaw. Cut a piece of plexiglass to fit, then attach to the cooler using epoxy.

1. chamber that's twice as big as the animal
    
2. tank of carbon dioxide gas (available in several sizes such as 6 lb., 20 lb., 50 lb., and 60 lb. If you don't need to lug it around, a larger tank might be cheaper to refill.)
    
3. hose or rubber tubing
    
4. flow regulator
    
5. commercial carbon dioxide chambers are available in different designs
    
6. check with welding suppliers; you may be able to rent some of this equipment

Equipment tips

1. Choose a chamber that can hold a large cage trap so you don't have to handle the animal. This is safer for you and less stressful for the animal.
    
2. The animal should be able to sit and rest comfortably within the chamber.
    
3. If the chamber is too tall, or if the vent hole is too low, the animal may be able to lift its head above the level of CO₂ gas, which would make the process take longer.
    
4. The chamber is NOT supposed to be airtight! Air must be able to escape to leave room for the carbon dioxide. Carbon dioxide is heavier than air, so it fills from the bottom up (like filling a glass of water). A vent hole near the top of the chamber or a loosely-fitted lid will let out the air but not the CO₂. The vent hole will also prevent pressure buildup.
    
5. Have a spare tank of CO₂ ready.
    
6. Don't mess around with dry ice, fire extinguishers, car exhaust, or antacids as sources of carbon dioxide. They will not work reliably.

Technique tips

1. Always work in a well-ventilated space to minimize your exposure to the CO₂, which can be dangerous to people, too.
    
2. Attach the hose from the CO₂ tank to the bottom of the chamber.
    
3. Ideally, carbon dioxide should enter the chamber at a rate that displaces 20% of the oxygen each minute (more on this later).
    
4. Should you fill the chamber with CO₂ before putting the animal in it? (This is called "precharging.") Some experts say "yes," others "no." Precharging will speed up the process but many animals will react violently to high concentrations of CO₂ if they're awake. It's less stressful to expose the animal to the gas at a carefully controlled rate. Right now, we say "no," but watch for more research.
    
5. Even if you have a commercial carbon dioxide chamber, you may want to consider building your own mobile unit.
    
6. The chamber should be cleaned and aired out between uses. (A good reason to have more than one chamber.)

Next Section (using a CO₂ chamber step-by-step)