For example, for the Gases under pressure hazard class, the hazard categories are Compressed gas, Liquefied gas, Refrigerated liquefied gas and Dissolved gas. These classes relate to the physical state of the gas when packaged and do not describe the degree of hazard.
1 In 1596, a flush toilet was invented and built for Queen Elizabeth I by her Godson, Sir John Harrington. 2  The first patent for the flushing toilet was issued to Alexander Cummings in 1775. 3  During the 1800s, people realized that poor sanitary conditions caused diseases.
Clearly, modern plumbing has come a long way. Here are 10 fun facts you may not know about your pipes. The first flushing toilet is credited to King Minos of Crete in 18th century B.C. However, the oldest Neolithic village in the UK, Skara Brae, had a primitive flushing system 1200 years prior.