The act of seeking to prevent the spread of and extinguishing major undesired fires in buildings, vehicles, and woods is known as firefighting. A fireman puts out flames in order to safeguard people, property, and the environment. Firefighters often receive extensive technical training. They may work at fire stations or at fire sites with other firefighters or alone. The term "firefighter" can apply to various types of personnel who fight fires. These include but are not limited to fire officers, fire marshals, fire investigators, emergency management officials, and civilians who participate in fire suppression activities. In some countries such as the United States, only officers can go through officer candidate schools where they learn skills necessary to fight fires. Other individuals who participate in fire protection activities may be called "firefighters", but they would not have this role specified on their job description. In general, there are two main types of firefighters: those who fight structure fires, and those who fight wildland fires. Structure fires involve burning of wood and wooden products such as furniture, barrels, boxes, and trees. They are usually caused by smoking materials such as cigarettes, cigars, pipes, herbs, and marijuana. People sometimes sleep with candles or lamps on at night which can lead to the death of everyone in the house if not put out quickly enough.