Gracie, a 6-month old Boxer-Great Dane mix, died when her choke collar got tangled while playing with another dog at a training center.  By the time the staff intervened by cutting the collar off with wire cutters and administering CPR, she was too far gone.
The Humane Society of the United States says that it is best for your dog if you avoid using one  and I agree. Choke collars function by causing pain and can injure the esophagus, trachea and neck. They can cause nerve damage as well as damage to the blood vessels in the eyes. To see a dog coughing because of the pressure applied with one is distressing.
Choke collars are an aversive training tool and are not used by trainers who stick with positive reinforcement methods. Other options such as head collars and front-clip harnesses are effective at preventing pulling. Additionally, positive reinforcement techniques are more effective for training dogs since dogs learn what to do rather than learning what not to do through punishment.
Gracie’s guardian did not initially use a choke collar, but the training center had a policy that all dogs had to wear one. They have since changed this policy and use martingale collars instead. If adjusted properly, these limited-slip collars tighten around a dog’s neck but cannot tighten enough to choke a dog.
Though I’m not a fan of choke collars, I understand that there are people who will still choose to use them. Two important safety tips can save the life of a dog who wears one: 1) Never allow a dog to play with other dogs while wearing a choke collar. 2) Never leave a choke collar on an unattended dog. There is some disagreement over whether Gracie and the other dogs involved were unattended when the incident occurred, but certainly unattended dogs are at greater risk of an accident than those who are under human supervision.
Accidents can happen with collars of any type, but choke collars are particularly risky. Choke collars are true to their name—designed to tighten around a dog’s neck with no mechanism to limit how tight they can become—and unfortunately, being choked by one is what happened to Gracie.