It's good to have a proper shelf at home, when the bushfires or fires happen, the smoke will occur around the house.
When you place your books in a proper shelf, the smoke will only damage the top of the book and the spine, other parts will not be damaged as serious.
When the book is in an open space without the construction of a shelf, moisture, smoke and other issues will occur easily.
Even without any fire threat, a bookshelf will keep books dry.
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