Tempered safety glass is glass that has undergone a chemical or thermal treatment to toughen the glass. Outer surfaces are compressed and tension is put on the inner surfaces; resulting in glass that shatters into small pieces instead of large shards when broken.

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Because of this trait, federal building codes require safety glass in specific areas of a property. All glass doors, like patio doors, must use tempered safety glass; as well any windows 60 inches from a stair tread or door (excluding decorative glass or glass less than 3 inches tall or wide). In bathrooms, all shower doors or glass 60 inches from the floor or lower in the bathing area are required to be tempered glass. Some local municipalities have additional codes beyond federal regulations.