There are two main types of fire extinguishers: stored-pressure and cartridge-operated. In stored pressure units, the expellant is stored in the same chamber as the firefighting agent itself. Depending on the agent used, different propellants are used. With dry chemical extinguishers, nitrogen is typically used; water and foam extinguishers typically use air.
The Encyclopedia Britannica, which has been in continuous print since it was first published in Edinburgh in 1768, said today that it will continue with digital versions currently available online. The final set of the 32-volume printed edition remains available for sale on the company's website for Â£890 ($1,400). Scroll down for video
When they saw how enthusiastically people embraced the notion of an encyclopedia that anyone could edit, Wales and Sanger quickly made Wikipedia their main project. By the end of its first year it had more than 20,000 articles in 18 languages, and its growth was accelerating fast. In 2003, Wales formed the Wikimedia Foundation to operate the servers and software that run Wikipedia and raise money to support them.