The exterior is completely metal and the only other exposed material on the outside is concrete.

BBC: California faces up to year-round forest fires

"Ending the exemptions from age classification for hard copy music videos will be an important step forward in making sure that children are not inadvertently exposed to unsuitable material, " said Mr Bailey.

BBC: Age-ratings call for music DVDs

The material is exposed to ultraviolet light through a mask patterned with the outlines of cells.

ECONOMIST: REPORTS