Uses liquid propylene instead of liquid inert hydrocarbon diluent. Each tank was pressurized with inert nitrogen gas. They are referred to as noble gases or inert gases. This layer makes bulk lead effectively chemically inert in the air. Taconite tailings are mostly the mineral quartz, which is chemically inert. It is chemically inert and monatomic in all standard conditions. Niobium and some niobium alloys are physiologically inert and hypoallergenic. It is relatively chemically inert, which contributes to its longevity. Stainless steel is generally considered to be biologically inert. Disinfectants are chemical agents designed to inactivate or destroy microorganisms on inert surfaces. PEG is generally considered biologically inert and safe. Suicide bags have been used with gases other than inert gases, with varying outcomes. Xenon is a member of the zero-valence elements that are called noble or inert gases. Pyrolysis is the thermal decomposition of materials at elevated temperatures in an inert atmosphere. Lime plaster is a mixture of calcium hydroxide and sand (or other inert fillers).