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Medicine for the Outdoors

Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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The Desert and Desert Survival 4

This is the sixth post based upon educational sessions and syllabus material presented at the Wilderness Medical Society Annual Meeting & 25th Anniversary held in Snowmass, Colorado from July 25-30, 2008. This post continues the discussion about the desert and desert survival, based upon the extensive knowledge of Dr. Edward J. (“Mel”) Otten, who is Professor of Emergency Medicine and Pediatrics, and Director of the Division of Toxinology at the University of Cincinnati.

Desert shelters are of three main types: 1) Natural shelters are caves and rock overhangs. When using natural shelters, remember there may already be other inhabitants that need eviction. Rattlesnakes, tortoises, ground squirrels, lizards, andskunks often use caves and other cool areas during the heat of the day. They may be sources of food, but are also potentially dangerous to humans. Some reptiles are venomous and many mammals carry rabies or plague. They can usually be removed with a stick or dispatched with a rock. 2) Man-made shelters include tents, vehicles, and buildings. Most vehicles become very hot and may hasten heat illness and dehydration. It is better to sit in the shade of an automobile than to be inside it during the heat of the day. Tents and buildings are best if there is adequate ventilation. 3) Improvised shelters are typified by the desert trench shelter, shade shelter or lean-to. Any structure that provides shade, protection from wind and blowing sand, and decreases heat gain or loss is minimally adequate.

The hottest area in a desert climate is at the surface of the ground, so getting above the ground or below the ground decreases exposure to the highest temperatures. Most desert animals take advantage of this fact by their behavior. Birds perch high in trees in the shade of a branch or in some cases inside of a cactus. Most mammals and reptiles will burrow into the ground, where just three feet below the surface the temperature may be 30% cooler. Humans can imitate this behavior by construction of a desert trench shelter. This is a trench dug in the ground 2 to 4 feet wide and 2 to 3 feet deep and about 6 feet long. A barrier can be made of any cloth material at hand, such as a blanket, sheet, poncho, tarp, or space blanket. This barrier is placed over the trench, about 18 inches above the bottom and the sides are weighed down with rocks or sand. Another similar barrier ( the first one can be doubled back on itself if it is large enough) is about 12 to 18 inches above the first barrier and also weighed down. This construction creates an insulating barrier that traps cooler air in the bottom of the trench and reflects solar radiation from the top. Ideally a reflective space-type blanket is used for the outer layer, which will increase the amount of heat reflected .

Removing the seat from a vehicle and sitting above the ground in the shade of the vehicle or constructing shade with a blanket or tarp and available materials can provide some shelter in the heat of the day until a more adequate shelter can be built. At night, when temperatures drop, the shade trench remains warmer due to heat produced by the inhabitant. The top barrier, with its reflective surface, can be reversed to reflect heat back into the trench. Any insulating material can be added to the floor of the shelter to decrease heat loss to the ground. Given enough time, shelters such as a tepee, tent or lean-to can be constructed using tarps, blankets, parachute panels, or other materials. Construction should take place in the cooler times of the day to conserve sweat and water. If you have a reliable source of water, such as a desert water hole or ”tank” (natural collection of water in nonporous rock) then it is best to stay where you are and try to be rescued rather than attempting to travel large distances without adequate water.

Food is not as immediate a problem as water in the desert. Most humans have an extra 50,000 to 70,000 calories that they store in the form of fat, and can exist for weeks without eating. Food in the form of animals or plants is usually available if water is available. Cactus fruit, such as prickly pear, can be eaten when peeled. Legumes such as acacia, mesquite, and palo verde produce beans that can be crushed and mixed with water to form tortillas. Yucca stems, cattails, agave stems and prickly pear pads can be cooked and eaten. Avoid plants with milky saps or red berries, and other plants that cannot be positively identified as edible. Mushrooms should not be eaten. It is essential to become familiar with the common poisonous and edible plants in any area through which you will travel. Insects, bird’s eggs, grubs, tortoises, and other slow movers can be captured by hand. Most small animals, such as snakes, lizards and birds, can be killed with a rock or stick. Jackrabbits, ground squirrels, and rats may be snared or trapped. Large mammals should be avoided, as the likelihood of killing one of these without a firearm is small, while the likelihood of becoming a casualty is high. All meat should be cooked or dried prior to ingestion. Animals avoid as food or in general include caterpillars, spiders, scorpions, centipedes, millipedes, toads, and bats, as well as some mammals that carry plague, tularemia, Hanta virus and rabies.

In addition to the hazards of heat and dehydration, there are other hazards that one may encounter in the desert. Blowing sand and dust created by vehicle traffic may cause eye, nose, mouth and skin irritation. Desert winds up to 100 mph can blow for days, creating immense sandstorms and dust storms that can cover large areas reducing visibility to near zero. In addition, vehicles, tents and buildings can be demolished and roads obliterated. Sandstorms blowing for days have caused destruction in cities such as Melbourne and Bagdad. Exposed skin must be protected and getting to hard sided shelter such as a building is preferable. The possibility of an individual being buried is remote but drifting sand can block doors and strand vehicles.

Quicksand is another hazard that travelers must watch. There are two types of quicksand: 1) A mixture of sand and water found along the shores of lakes and seas and estuaries of rivers. This type make appear solid, but is a suspension of fine sand and water and cannot compact. 2) Fine sand deposited by wind in hollow depressions. Depending on the depth of the depression one could sink 15 to 20 feet. If one is caught in quicksand, attempt to escape by flattening out and swimming to firm ground. Most quicksand ,areas are small. Animals will panic and struggle hastening their submersion. A rescuer can usually pull the victim to firm ground using a rope, belt or strap. Removing one’s pack and throwing it to firm ground will also allow for easier escape.

Animal hazards include venomous snakes and arthropods, carriers of zoonotic illnesses, and large mammals. Plant hazards include poisonous varieties that may cause dermatitis or systemic symptoms if ingested. Many types of plants produce spines, thorns, which when broken off in the skin, commonly cause infections.

Even in the best of circumstances, hiking in the desert can be difficult. Most modern travel is performed with high clearance, 4 wheel drive vehicles. These vehicles should have sand mats (for added traction in soft surfaces), and a winch and cable for self-extracting the vehicle or rescuing another vehicle. Extra water, spare parts for the vehicle ( fan belts, hoses, spark plugs, fuses, bulbs), additional fuel and oil, shovel, two jacks, spare battery, spare tires and tire patching materials, radio and tool kit are mandatory in desert travel. Traveling in convoys is a must both for safety and in someplaces, security. Salt flats, mud flats and soft sand can bog down even 4 wheel drive vehicles. Never attempt to cross arroyos or wadis when they are flooding.

Many areas have no access to wheeled vehicles and travel by camel, donkey, or horse is still common. Camels are still the most efficient desert transportation and can travel for long periods without food or water . They also are more resistant to blowing sand, heat and temperature changes. Expert assistance is needed for travel by camel. Horses and donkeys are limited to short distances and require more food and water. Current topographic maps and a good compass are essential whether traveling by vehicle, animal, or on foot. Local authorities should be consulted concerning water sources; these should be marked on the maps. A copy of the map should be left with someone who knows your plans. Your route and campsites should be indicated on the map. In that way, if one becomes lost or injured the search and rescue teams will know where to initiate the search.

If one becomes lost or injured, it is usually best to stay in one place and signal for help, using a mirror or other reflective object during the day and a fire at night. Cellular telephone, radio, or emergency locator transmitter may aid searchers. Flares and whistles should be used only when searchers are nearby or a search aircraft is moving in your direction. Geometric patterns drawn on the ground, such as “SOS”, “HELP” or a large “X”, may aid aircraft in identifying the position of a distressed person. Rocks, contrasting soil, plants, or clothing can be used to produce the patterns. It is difficult to see a single human being on the ground; therefore, it is always best to stay near a vehicle if possible. An automobile can be a good source of signaling equipment. The windscreen and windows reflect light, and the mirrors can be removed and used to signal. Oil can be drained, placed in a hubcap, and mixed with sand. When set on fire it produces dense black smoke. The hubcaps can be used to dig a desert trench shelter, the battery to start a fire, and the seat covers and floor mats for shelter and footwear. If one has adequate water, knows the direction of travel, has good footgear, and decides to try to walk to safety, it is imperative to leave a note outlining plans in a conspicuous place or to draw an arrow on the ground with rocks pointing in the direction of travel. Direction finding can be accomplished without a compass using the sun or stars.

Before traveling in the desert, it is best to know the location of the key terrain features, such as rivers, highways, mountain ranges, and cities. Power lines, stream beds, and pipelines may also lead to civilization, but it may require days to arrive. It is dangerous to travel through arroyos or wadis because of the danger of flash flooding. Rainfall in mountains several miles away can wash down these formerly dry stream beds, pushing tons of mud, rocks and water in a lethal torrent. Sand dunes should be avoided because of the amount of energy required to traverse them and salt marshes may contain soft ground that traps the hiker. Travel in the cool of the night to conserve water and use the stars for direction. The dangers at night are that many desert animals are more active and the chance of falling from a cliff, stepping into a hole or stumbling into a cactus is greater.

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About the Author

Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.