Mountain climbers in the Himalayas often experience altitude sickness because they are not used to being so high up. If a guest discovers a fire, he or she should alert other guests and staff in the hotel by setting off the nearest fire alarm and then evacuating the building. Airlines recommend that passengers should do light exercises during long haul flights to avoid deep vein thrombosis. Passengers on a commercial flight should listen carefully to the safety announcement, read the safety card in the seat pocket in front of them, and take note of where the emergency exits are. Nausea caused by being in a moving vehicle is called motion sickness. It is also called air sickness when traveling in an aircraft. Smoke detectors should be installed in corridors and in all rooms, and tested on a weekly basis. Their batteries should be changed every six months. E. coli and Salmonella are just two of the bacteria that can cause very serious food poisoning. There are two fire extinguishers on each floor to use in the event of a fire. One of these contains carbon dioxide and one contains water. Before traveling to some countries, it is necessary to receive immunization against some of the diseases you could catch. Many travelers experience an upset stomach when they visit foreign countries, usually as a result of a change in diet, but sometimes as a result of poor hygiene in restaurants.