Many a shop has gone up in FLAMES in these parts,due to this(spontanious combustion).To play it safe,and prevent a flaming rag,wiper ,whatever.The rag, will NOT combust,if it is layed out FLAT with no wrinkles, or, folds in it..It needs to be wadded up, or folded(that`s what makes the excessive heat),for it to ignite.I myself, have never heard ,or, seen, of used ,dry rags, doing this.But, what I personally do is DRY them Flat ,outdoors on the grass,and then put them(when dry) in a metal, fire-proof container.A 1-5 gallon steel paint can ,and lid, works great, and costs nothing in most cases.Put your dried ,used rags,in the can ,and, put the lid on it( tightly).Till they can be disposed of.If air can`t get at the Rags, they can`t burn(got to have oxygen).The only time ,I`ve heard or Dry used rags igniting, was from a spark landing on it,but a pile of, new, unused rags, will do that (burn )too.I should also mention, that this condition can happen to the Automotive enthusiast too.GREASY ,and, oily rags, will spontaniously combust as well.So please use the paint can, for those types of rags,as well.Nothing worse,than, seeing a Grown man cry,when everything is lost,(tools models, etc.) Due to a fire, that could have,easily been prevented.Especially, when the fire Marshall tells him, that the cause of the fire, was, from a real hot spot, in the corner"A pile of rags, maybe"?.

Guys no need to be afraid ,Just be aware,is all.