Texts for listening heat transfer

Heat can travel throughout a burning building by one or more of four methods: conduction, radiation, convection, direct flame contact. The existence of heat within a substance is caused by molecular action. Thus, as the vibration of the molecules becomes more intense, the heat becomes more intense. Since heat is disordered energy, it never remains constant but is continually transferred from objects of higher temperature to those of lower temperature. The colder of two bodies in contact will absorb heat until both objects are the same temperature.

Heat may be conducted from one body to another by direct contact of the two bodies or by heat-conducting medium. The amount of heat that will be transferred and its rate of travel by this method depend upon conductivity of the material through which the heat is passing. Not all materials have the same heat conductivity. Aluminum, copper, and iron are good conductors. Other solids such as stone and wood are poor conductors. Fibrous materials, such as felt, cloth, and paper are poor conductors. Liquids and gases are poor conductors of heat because of the free movement of their molecules. Air is a very poor conductor. Double building walls which contain an air space provide additional insulation.

The next method of heat transmission is known as radiation of heat waves. Heat and light waves are similar in nature but they differ in length. Heat waves are longer than light waves and they are sometimes called infrared rays. Radiated heat will travel through space until it reaches an opaque object. As the object is exposed to heat radiation it will in return radiate heat from its surface. Radiated heat is one of the major sources of fire spread.

Turntable ladders

A turntable ladder, also known as an aerial ladder is the best-known form of specialized fire apparatus. Turntable ladders are used to rescue people from high-rise buildings or help firefighters to get access to fires occurring at height if they cannot get in through the lower floors and where other ladders can’t reach.

The name is derived from the fact that the large ladder is mounted on a turntable on the back of a truck, allowing it to move around a stable base, which in turn allows to achieve a much greater ladder length. In order to increase its length, the ladder is telescopic. Modern turntable ladders are hydraulic or pneumatic in operation.

In some cases, there may be a monitor at the top of the ladder. It can pump up to 1000 litres of water per minute down, or up, onto a fire that may be otherwise inaccessible to the crew below. Some turntable ladders may have a basket or platform mounted at the top of the ladder, and these are called tower ladders. These can provide a secure place for a firefighter to operate equipment from, and allow multiple people to be carried (including rescued persons).

The key functions of a turntable ladder are:

• Allowing access and escape of firefighters and victims at height;

• Providing a high level water supply for firefighting;

• Providing a working platform from which tasks such as ventilation or overhaul can be executed.

Turntable ladders are constructed of metal and are trussed to provide adequate strength. Their usual weight is 14 tones. The ladders generally range in length from 65 to 100 feet, but longer turntable ladders do exist. The usual width is 2,4 m. The ladder can reach up to 30 m in height. Since firefighting takes places in a very hot and dangerous environment with high risks, firefighters work in pairs. That is why the crew of two people operates the ladder.