Twelve of the vertical tubes contained control rods made of boron carbide powder inside steel tubes. These could be raised and lowered to control the reaction, with any seven inserted being enough to absorb sufficient neutrons that no chain reaction could happen. The rods were held up by electromagnets, so that a power failure would cause them to fall into the tubes and terminate the reaction. A pneumatic system could use air pressure from above to quickly force them into the reactor core or from below to slowly raise them from it. Four of these were called the "safeguard bank" while the other eight were controlled in an automatic sequence. Two pushbuttons on the main panel in the control room activated magnets to seal the rods to the pneumatic system, and the pushbutton to cause the pneumatic insertion of the rods into the core was located a few feet away.