Ecology is the study of the relationships between living organisms, including humans and their physical environment. The German scientist Earnst Haeckel was the first to use this word in 1869.

Acetylene is the only fuel gas suitable for gas welding because of its favourable flame characteristics of both high temperature and high propagation rates. Other fuel gases, such as propane, propylene or natural gas, produce insufficient heat input for welding but are used for cutting, torch brazing and soldering.

Most building codes require ceiling fans to be mounted on special fan-rated boxes made of metal or strong plastic with deep-threaded holes for the mounting screws. The box must be mounted firmly by attaching it directly to a framing member or using a fan-rated brace.