Firefighting is the act of extinguishing or preventing the spread of unwanted fires from threatening human lives and destroying property and the environment. A person who engages in firefighting is known as a firefighter. Firefighters typically undergo a high degree of technical training. This involves structural firefighting and wildland firefighting. Specialized training includes aircraft firefighting, shipboard firefighting, aerial firefighting, maritime firefighting, and proximity firefighting. Firefighting is a dangerous profession due to the toxic environment created by combustible materials, with major risks being smoke, oxygen deficiency, elevated temperatures, poisonous atmospheres, and violent air flows. To combat some of these risks, firefighters carry self-contained breathing apparatus. Additional hazards include falls — a constant peril while navigating unfamiliar layouts or confined spaces amid shifting debris under limited visibility – and structural collapse that can exacerbate the problems encountered in a toxic environment. The first step in a firefighting operation is reconnaissance to search for the origin of the fire and to identify the specific risks. Fires can be extinguished by water, fuel or oxidant removal, or chemical flame inhibition; though, because fires are classified depending on the elements involved, such as grease, paper, electrical, etcetera, a specific type of fire extinguisher may be required. The classification is based on the type of fires that the extinguisher is more suitable for. In the United States, the types of fire are described by the National Fire Protection Association. History The earliest known firefighters were in the city of Rome. In 60 A.D., emperor Nero established a Corps of Vigils (Vigiles) to protect Rome after a disastrous fire. It consisted of 7,000 people equipped with buckets and axes who fought fires and served as police. Historic tactics and tools In the 3rd century B.C., an Alexandrian Greek named Ctesibius made a double force pump called a siphona. As water rose in the chamber, it compressed the air inside, which forced the water to eject in a steady stream through a pipe and nozzle. In the 16th century, syringes were also used as firefighting tools, the larger ones being mounted on wheels. Another traditional firefighting method that survived was the bucket brigade, involving two lines of people formed between the water source and the fire. Typically, men in one of the lines would pass along the full buckets of water toward the fire while in the other line women and children would pass back the empty buckets