If the dropped ceiling is used as a plenum, low-voltage cables and wiring that are not installed inside conduit must use a special low-smoke and low-toxicity wire insulation, which will tend to char and stop burning on its own. That helps to protect building occupants so that they are not poisoned with toxic chemicals sucked through the ventilation system during a fire, and it helps to prevent fires from spreading inside the hidden plenum space. The special low-smoke cable is typically referred to as plenum cable or Low Smoke Zero Halogen (LSZH or LS0H) cable. While twisted pair cable for networking and telephone service is the most common form of plenum cable, coaxial cable also needs to be plenum-rated for safety.