Safety was listed as the most important customer requirement for our engineering design process, therefore it is very important to understand the current safety concerns regarding C-BCI technologies.
BCI systems use a wide range of Operating principles to function, as a result the safety considerations vary between devices. For Consumer purposes however, Electroencephalography is by far the most common operating principle, therefore this section will be particularly applicable the safety considerations regarding EEG C-BCI devices. However, many of these dangers apply to other methods as well.
Unlike the mental dangers, the physical dangers of BCI's are thankfully very simple to understand and make very good sense. Most BCIs measure electrical activity within the brain, this means that there are wires connecting to parts of a person's brain and then going through to circuitry and a computer. Any sort of electrical discharge to the brain through these wires can cause catastrophic damage, equivalent to defribullating the heart. This normally manifests as a seizure with loss of consciousness, and may cause the victim to suffer from seizures permanently. Brain damage is also a risk if a higher current is sent to the brain. BCI devices are designed to counter this, with many safety features in-place to prevent malfunction. However, it is unavoidable that there is a connection from the brain to circuitry if the BCI is to function, and if a static charge builds on the computer or any point along the connected circuit, and the user touches that area and completes the circuit, the static charge will travel right through the brain. This is less dangerous than a direct discharge through the electrodes, but can still cause seizures.
Mental Dangers - An Ethical IssueEdit
The use of BCI devices in their current form (particularly with EEG which provides relatively poor data) relies more on our ability to send a signal to the computer, than the devices ability to read signals in our brain as they naturally occur. Due to this fact, a certain amount of training and practice is required to use a BCI effectively. Interestingly, this is synonymous with Neurotherapy (also known as Neurofeedback), a practice increasingly used to treat epilepsy, ADHD  and panic attacks. As a result, use of BCI devices is warned to have the possibility of impacting the personality of the user. The OpenEEG group is particularly concerned about this, with a very large caveat posted on their site , a portion of which is shown below: 
It is shown that a repeated BCI function (such as character movement in a game) can alter the neural connections in the brain. Current research shows that these changes return to normal after 20 minutes, but repeated use for extended periods of time (People play individual games for 100s of hours) may have a more serious and permanent effect.
"Neurofeedback training in itself can also cause unpleasant side-effects for a small number of people, or in certain unusual circumstances. In an attempt to provide information to allow you to better judge the risks to yourself, we are listing here the ones we are aware of. As we are not experts, and you should research the subject yourself if you want to be sure. - Increased anxiety leading to tics, insomnia or even panic attacks. - Stimulation of latent seizure activity to full (epileptic) seizure activity. - Mood changes, such as depression or anger outbursts."