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.
Option 1 - Facing and hearth same width-and they are not overly narrow. If your facing and hearth are wide enough (usually at least 70 or more) you can select nearly any of our mantels to fit entirely on top of the hearth as illustrated below. Most designers will suggest that the mantel shelf not be any wider than the facing on the wall (although in some instances this cannot be avoided).