The vacuum tube in a CRT can implode if it is broken or punctured. The surrounding air will rush violently into the unsealed vacuum in the CRT, spraying broken glass in every direction. Color CRTs may contain mercury or other potentially toxic materials.
Instructions. Build a hearth for a fireplace that is 16 inches deep, according to This Old House writer Harry Sawyers. This is the standard requirement for municipalities and homeowner associations. The hearth should also extend a minimum of eight inches on either side of the fireplace.
Hearth extensions shall extend not less than 16 inches (406 mm) in front of and at least 8 inches (203. mm) beyond both sides of the fireplace opening. 5. Factory-built fireplaces shall be installed in accordance with their listing and the manufacturer's installation. instructions. 6.