- Carbon monoxide (CO)
- An odorless, colorless gas given off by generators, grills, camp stoves, and engines. It kills in enclosed spaces. Keep a battery-powered detector near the bedrooms. See chs. 4, 9, and 18.
- CERT (Community Emergency Response Team)
- Community Emergency Response Team. A free course for neighbors: fire safety, light search and rescue, disaster first aid. See ch. 1.
- Check-Call-Care
- The American Red Cross's basic sequence: check the scene and the person, call 911, and then give first aid. See ch. 7.
- Chlorine dioxide
- Tablets or drops for disinfecting water. They also work against Cryptosporidium if you follow the label's wait time. See ch. 3.
- Clove hitch
- A quick knot for tying a rope to a post or pipe. It can come loose if the post rotates or the load shifts; secure it with half hitches. See ch. 17.
- COLD rule
- A rule for dressing in the cold: Clean, avoid Overheating, Loose, in Layers, Dry. See ch. 14.
- Cold shock
- A gasping reflex and uncontrolled breathing when suddenly falling into cold water. In the first minute it is more dangerous than hypothermia. See ch. 13.
- Contraflow
- Using the opposite-direction lanes of a highway to evacuate. In hurricanes, your state's highway authorities may activate it on the main routes leading away from the coast. See chs. 10 and 24.
- Cooling or warming center
- A public place with air conditioning or heating that the city opens during heat or cold waves. Ask about hours and whether pets are allowed through your city's services line (311 in many cities). See ch. 10.
- Cooper's color scale
- A way of thinking about your level of attention: white (distracted), yellow (alert and relaxed), orange (something is off), red (act: get away). In public, avoid white. See ch. 25.
- Corsi-Rosenthal box
- A homemade air purifier: a 20-inch box fan with MERV 13 furnace filters taped to it. It works for smoke and dust, not for gases. See ch. 18.
- Cospas-Sarsat
- An international satellite system that receives the distress signal from beacons (PLBs and EPIRBs) at 406 MHz. See ch. 8.
- CPR
- Cardiopulmonary resuscitation: hard, fast compressions in the center of the chest, at least 2 in (5 cm) deep, 100–120 per minute, with or without breaths. See ch. 7.
- Cryptosporidium
- A waterborne parasite highly resistant to chlorine. It is eliminated by boiling, with a filter of 1 micron or less, or with chlorine dioxide following the label's contact time. See ch. 3.
