When victims eventually submerge, they hold their breath for as long as possible, typically 30 to 90 seconds. After that, they inhale some water, splutter, cough and inhale more. Water in the lungs blocks gas exchange in delicate tissues, while inhaling water also triggers the airway to seal shut - a reflex called a laryngospasm. "There is a feeling of tearing and a burning sensation in the chest as water goes down into the airway. Then that sort of slips into a feeling of calmness and tranquility," says Tipton, describing reports from survivors.