SDI Open Water Scuba Diver Practice Exam

Which gas can cause extreme headache and nausea, and may turn lips and fingernail beds bright red?

1. Oxygen

2. Nitrogen

3. Carbon Dioxide

4. Carbon Monoxide

The correct answer is: Carbon Monoxide

Carbon monoxide is a colorless, odorless gas that can be particularly dangerous because it binds to hemoglobin in the blood more effectively than oxygen. This prevents oxygen from being carried throughout the body, leading to a condition known as carbon monoxide poisoning. The symptoms of this type of poisoning are significant and can include extreme headaches, nausea, dizziness, confusion, and even loss of consciousness. One of the most telling signs of carbon monoxide exposure is the bright red coloration of the lips and fingernail beds, which occurs due to the formation of carboxyhemoglobin — a compound formed when carbon monoxide binds to hemoglobin. In contrast, oxygen, nitrogen, and carbon dioxide do not typically present these specific symptoms related to exposure or poisoning. Oxygen, although essential for life, can lead to other issues in excessive amounts but does not cause headache and nausea in the same manner as carbon monoxide. Nitrogen is inert in the human body under normal pressure and does not produce those symptoms. Carbon dioxide can lead to headaches and shortness of breath if present in high concentrations but does not typically cause a bright red coloration of the skin and mucous membranes.