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.
Proper sizing is determined by the size of the fireplace base and the overall size of the Gas Log and Hearth Kit, which requires measuring the front width, back width, depth and height of the fireplace. Getting logs or controls too tight to the sides can cause damage to the fireplaces and gas log controls.