For emergencies, call 911 (or 9-911 if you are calling from a room in one of the park lodges). Emergency phones at ranger stations connect directly to the park switchboard and do not require coins. Your cell phone isn’t likely to get a signal inside the canyon or on the North Rim. River guides carry satellite phones and are trained to assist in emergencies. Rangers and clinic staff handle emergencies on the South Rim, where a walk-in clinic (928/638-2551) is open all year. You can fill prescriptions here, but only with a handwritten order from your doctor. Flagstaff Medical Center is about 90 minutes from the South Rim by car. The North Rim is more remote, and park rangers have first-aid certification or EMT training. The nearest small hospitals are in Page (125 miles) or Kanab, Utah (82 miles). Air transport to Flagstaff Medical Center is possible from either rim.
Elevations range 6,600–7,400 along the South Rim  and 8,200–8,800 on the North Rim , high enough to affect many flatlanders, especially the elderly or those with existing health problems. Signs of altitude sickness are headache, weakness, fatigue, shortness of breath, and dizziness. Dehydration is often a factor, so drink plenty of water. Taking a day or two to acclimate before hiking helps, as does slowing your pace and taking rest breaks.
A family trip to Grand Canyon turned into tragedy in 2007, when a four-year-old girl fell 450 feet to her death, and her father was injured trying to reach her. Every year, falls at Grand Canyon result in injuries and 1–3 deaths. Many of the victims were trying to get a photograph or scrambling around on rocks outside guardrails.
Keep a close watch on kids (and a closer watch on your husband or boyfriend—most victims are young men). Stay behind fences and barriers and be cautious near the rim: Even large rocks can break loose, icy patches are common in the winter, and sand or small rocks make surfaces slippery any time of year.
If you’re hiking, don’t cut switchbacks or go off-trail, and step to the inside of the trail and wait for mules to pass. The canyon’s terrain is rugged, and it’s a long way down.
High altitude, dry air, and hot summer temperatures multiply the effects of the sun. Below the rim, the canyon’s rocky walls hold heat and reflect the sun’s rays. Extreme inner canyon heat catches many people unprepared, and heat-related conditions are common. Protect yourself from sunburn by wearing a wide-brimmed hat, UV lenses, sunscreen or long sleeves, and lip balm. Above all, drink plenty of water.
Because the hot, dry air quickly dries perspiration, hikers may not realize how much moisture they are losing from sweat—up to two quarts of water every hour. Rangers along the Bright Angel Trail  treat as many as 20 cases of heat exhaustion daily during summer months. Symptoms are pallor, nausea, headache, cramps, and cool, moist skin.
Left untreated, heat exhaustion can lead to heatstroke, a life-threatening emergency. The face becomes flushed and the skin dry. The pulse is weak and rapid. The body’s ability to regulate temperature is overwhelmed, and body temperature goes up, leading to mental confusion and eventual unconsciousness.
Hyponatremia (water intoxication) can look like heat exhaustion, with cramping, clamminess, headache, and nausea. But this serious condition is the result of drinking too much water without replacing electrolytes, leading to low concentrations of sodium in the blood. Like heatstroke, hyponatremia can lead to altered mental states and rapid pulse, and it too can be deadly.
To prevent heat-related illnesses, drink plenty of water and balance water intake by eating salty snacks and/or using electrolyte-replacement powders, gels, or drinks. Keep cool, resting in the shade and hiking within your abilities. If your hiking companion’s mental state becomes altered, get immediate help. If you suspect heatstroke, cool the victim immediately by pouring water on his or her skin, clothing, and hair.
With so many dire warnings about dehydration and heat, it’s easy to forget that hypothermia is also a danger. Exposure to cold and wet conditions can lead to the point where the body can’t warm itself. Symptoms are the “umbles”: mumbling, grumbling, stumbling, fumbling. If you’re hiking during the winter, wear fleece rather than denim or heavy cotton, and pack a Thermos with a hot drink. Treat hypothermia with dry clothing, warm liquids, and protection from the elements.
Do not hike in tributary canyons when flash floods are a possibility, particularly during the late-summer thunderstorm season. Boaters should always wear a personal flotation device (PFD) or life jacket. Colorado River currents are swift, with bone-chillingly cold water and dangerous rocks and rapids. To protect beaches from ammonia buildup, campers and river runners urinate in the river or in the wet sand at the water’s edge. This can be a tricky proposition in the middle of the night when it’s dark and you’re sleepy. Carry a flashlight or headlamp, and be cautious on wet rocks.
The canyon is home to several biting insects, including scorpions and bees, as well as several species of rodents and rattlesnakes. If you are allergic to beestings or insect bites, carry an EpiPen and be sure your hiking companions know how to use it. Prevent bites by watching where you place your hands and feet. Shake out clothing and bedding. Don’t feed or pester wildlife. Although snakebites are rare, they are almost always the result of people trying to handle snakes. Deer, bighorn sheep, coyotes, and rock squirrels have bitten people offering them handouts.
Rabies and plague aren’t uncommon in Arizona. Never handle a bat; if you see one during the day, it is quite likely infected with rabies. Keep your food supply secured when you are in camp: Ringtails, rodents, and ravens can get into packs even when they are hanging, so consider using animal-proof containers. Hantavirus, a deadly respiratory illness, can be transmitted by inhaling dust from rodent waste. If you discover that your ziplock bag of GORP has been chewed into, pack it out with the rest of your trash.
Some hikers feel safer carrying a bite extractor, which works for removing poison or stingers from insect bites as well as for snakebite venom. Any animal bite should be checked by a physician and monitored for signs of infection.