There are many dangerous processes in cryogenic experiment. Cryogenic operators must understand cryogen characteristics and the structure and functions of basic cryogenic equipments, such as storage dewars, transfer tubes and compressed gas cylinders and some other useful instruments, such as level meters, manometers, flow meters, which are installed in the cryostat for safety and effective handling of cryogen. Precooling using liquid nitrogen is effective for liquid helium saving. But, according to circumstances, cool-down by making good use of gaseous helium would be a better selection from the view point of safety and experimental efficiency.
