The fear of being buried alive is an old one, and is even the origin of the phrase "saved by the bell". Annalee Newitz of io9 has a roundup of technologies developed over the years, right up to the present day, to prevent a person from meeting this fate. Pictured above is Thomas Pursell's 1930s-era tomb that featured doors that could be opened from the inside.
Link
*Facepalm*
http://www.youtube.com/watch?v=_dWCd54EA84