Mescalero-Chiricahua Apache is a family of languages that is spoken in Oklahoma and New Mexico. The Oklahoma language is in dire need of assistance; while most Indigenous languages in North America are in danger of extinction, this one has as few as three native speakers remaining.
Basic problems with corrosive chemicals... Corrosive: A chemical, (solid, liquid or gas), that can cause destructive damage to body tissues at the site of contact. It can cause severe burns to the skin and can eat through clothing, metal and other materials.
Compressible flow (gas dynamics) is the branch of fluid mechanics that deals with flows having significant changes in fluid density. Gases, mostly, display such behaviour. While all flows are compressible, flows are usually treated as being incompressible when the Mach number (the ratio of the speed of the flow to the speed of sound) is less than 0.3 (since the density change due to velocity is about 5% in that case).