Coal mining generates significant adverse environmental impacts. Historically, coal mining has been a very dangerous activity and the list of historical coal mining disasters is a long one. Underground mining hazards include suffocation, gas poisoning, roof collapse and gas explosions.
The term 'OVD' (Optically Variable Device) is used to describe both laser generated hologram images and electron beam generated images. These optically variable devices are created in highly-secure facilities and are at the forefront of overt asset and brand protection programmes.
Original video animation, abbreviated as OVA media, are animated films and series made specially for release in home video formats without prior showings on television or in theatres, though the first part of an OVA series may be broadcast for promotional purposes. OVA titles were originally made available on VHS, later becoming more popular on LaserDisc and eventually DVD. Starting in 2008, the term OAD began to refer to DVD releases published bundled with their source-material manga.