Flammable gases (e.g., hydrogen, methane, propane, acetylene) and oxygen (or other oxidizing gases) must be separated by 20 feet or by a non-combustible partition extending 18 inches above and to the sides of stored gas cylinders. Cylinders should be positioned so that the label with the name of the gas and its hazard is clearly visible. Gas cylinders are often difficult to reach; in an emergency, first responders need to see what they’re dealing with as quickly as possible.