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.
An OVA file is a virtual appliance used by virtualization applications such as VMware Workstation and Oracle VM Virtualbox. It is a package that contains files used to describe a virtual machine, which includes an .OVF descriptor file, optional manifest (.MF) and certificate files, and other related files.