Haystacks may also be built on top of a foundation laid on the ground to reduce spoilage, in some places made of wood or brush. In other areas, hay is stacked loose, built around a central pole, a tree, or within an area of three or four poles to add stability to the stack. One loose hay stacking technique seen in the British Isles is to initially stack freshly cut hay into smaller mounds called foot cocks, hay coles, kyles, hayshocks or haycocks, to facilitate initial curing. These are sometimes built atop platforms or tripods formed of three poles, used to keep hay off the ground and let air into the center for better drying. The shape causes dew and rainwater to roll down the sides, allowing the hay within to cure. People who handle the hay may use hayforks or pitchforks to move or pitch the hay in building haycocks and haystacks. Construction of tall haystacks is sometimes aided with a ramp, ranging from simple poles to a device for building large loose stacks called a beaverslide. Safety issues Farmer's lung (not to be confused with silo-filler's disease) is a hypersensitivity pneumonitis induced by the inhalation of biologic dusts coming from hay dust or mold spores or other agricultural products. Exposure to hay can also trigger allergic rhinitis for people who are hypersensitive to airborne allergens. Hay baled before it is fully dry can produce enough heat to start a fire. Haystacks produce internal heat due to bacterial fermentation. If hay is stacked with wet grass, the heat produced can be sufficient to ignite the hay causing a fire. Farmers have to be careful about moisture levels to avoid spontaneous combustion, which is a leading cause of haystack fires. Heat is produced by the respiration process, which occurs until the moisture content of drying hay drops below 40%. Hay is considered fully dry when it reaches 20% moisture. Combustion problems typically occur within five to seven days of baling. A bale cooler than is in little danger, but bales between need to be removed from a barn or structure and separated so that they can cool off. If the temperature of a bale exceeds more than , it can combust. To check hay moisture content, the farmer can use a hand, an oven or a moisture tester. The most efficient way is to use a moisture tester which shows