According to the search results, a blood alcohol concentration (BAC) of 0.40% or over is considered a lethal dose for most people. At this level, there is a risk of coma or death due to respiratory arrest. Symptoms of alcohol impairment can vary depending on the BAC level, but at a BAC between 0.08% and 0.40%, a person is likely to experience confusion, drowsiness, nausea, and loss of balance and muscle control. It is important to note that the effects of alcohol can vary depending on factors such as body weight, gender, and tolerance to alcohol. If someone is showing signs of an alcohol overdose, such as difficulty breathing, vomiting, or loss of consciousness, medical attention should be sought immediately.