Firefighters use hydraulic equipment on a daily basis when they put out blazes and rescue people from burning buildings or crashed vehicles. The ladder on top of a fire engine is raised and lowered by a hydraulic piston, that is controlled by the ground crew, with another set of hydraulic hoses controlling the extension of each section of the ladder independently, allowing the correct length of ladder to be deployed for each situation. The ladder position is also controlled by a hydraulic motor, that turns the ladder left and right, making it easy to get the ladder in exactly the right place by using all three hydraulic components. It is not just the firefighters ladder that uses hydraulic power, but the rescue and cutting tools, as well. Fire crews are often called upon to rescue people from crushed vehicles and getting them free is often a time sensitive operation, so the large forces exerted by hydraulic cutters, rams and spreading equipment are vital in terms of getting people free as quickly as possible. These tools operate at 720 bar, which is a large enough force to cut through steel rods and easily bend the structure of a car or lorry cab. Often referred to as the Jaws of Life, some hydraulic rescue equipment combines cutting and spreading capabilities into one tool, as both these functions are usually needed in rescue situations. Hydraulic jacks are carried on some fire trucks that are called to the scene of a heavy vehicle crash, as lifting a crashed train carriage or petrol tanker requires some serious force to be applied quickly, especially if there are people trapped underneath or inside the vehicle. The choice of hydraulic fluid is very important in fire engines, as by nature they are used in situations where high temperatures are present. The fluid used in hydraulic rescue equipment is usually a phosphate-ester fluid, that does not conduct electrical charge and is fire resistant. It is vital that the hydraulic fluid used is fire resistant and capable of operating at high temperatures. Hydraulic fluid does heat up under pressure, so adding this factor to the issues of prolonged exposure to high heat at fire scenes means that there are limited choices of hydraulic fluids for fire engines. If oil based hydraulic fluids are used there is a high risk of fire if a line breaks or there is a leak, so for safety reasons any fluids used on a fire truck must be non-flammable. Regular checks and maintenance of hydraulic fluid levels should be performed with any equipment that uses hydraulic fluids, but in the case of fire trucks it can make the difference between life and death. Fluid reservoir levels should be checked under the same conditions each time, which is best done when the fluid is cold and the fire engine has not been recently used. Keeping the reservoir topped up reduces the risk of air entering the system through the pump, which can lead to faulty operation and lasting damage to the components. This is a job that firefighters can carry out at their station, but for testing the hydraulic fluid a professional service should be used. The hydraulic fluid should be replaced regularly to keep the equipment in good working order. Each type of hydraulic equipment may use a different type of fluid, and it is important that these are not mixed up during routine maintenance. Most fire departments display the information clearly at the point of topping up on the inside of cap covers or nearby. It is also good practice to label the fluid containers so they are not accidentally used on the wrong engine or the wrong piece of equipment, as each fire department may favour a particular type of oil for each application, and when fire trucks are loaned out to other departments there is a serious risk of hydraulic fluid mix up.