Heat - A Silent Killer

Everyone knows tornadoes, hurricanes and other sorts of violent weather common to summer can kill you, but, under ordinary conditions, few of us think of heat as lethal. Stealthy and subtle, it can take you out with little warning and no one is entirely immune from it despite the protection and shelter modern life offers.

Summer in Chicago is hot and humid at best and brutally hot at worst. Its sea of buildings and roads make already hot days worse as they absorb and reradiate heat around the clock. Because of this, night brings no relief from heat. The poor suffer the most because they can’t afford air conditioning and their homes get very hot. The very young and old are the most vulnerable and are typically the main victims of heat waves. In July of 1995, an unusual combination of weather factors produced a heat wave in Chicago that killed over 700 people and put thousands more in the hospital.

Although they accurately forecast a heat wave that July, local weather teams didn’t take into account the rainfall that had occurred over several days prior. It left the ground saturated and the air above it very humid. A strong high settled in over the region and was amplified by a strong disturbance that moved eastward from the Pacific. To add to the danger, the upper level jet was weak in the area and the high stagnated, which kept the skies clear. All the while, the sun beat down relentlessly on the city.

Humidity continued to rise as warm, moist air was drawn northward from the Gulf of Mexico around the back of the stagnant high right into the region. Late evening humidity rose above 90 percent and created a strong inversion. The inversion layer was so warm, it kept the air below it from rising and pollutants in the surface layer rose steadily day by day.

Think of it; no wind, clear skies, unrelenting sunshine and a steadily increasing heat from the concrete and asphalt that is a city. Indoor temperatures at night remained above 104F where air conditioning wasn’t available. In safer times, whole families might have slept out on the roofs to catch what relief they could but that didn’t happen, especially in the poor neighborhoods. People stayed locked up in their homes with windows closed and curtains drawn.

By July 12th, area forecasters were issuing heat warnings every day and people were dying in droves. By July 15th, emergency rooms were flooded with heat casualties and deaths skyrocketed. On a single day, 162 people died of heat-related causes. When the crisis finally ended, more than 70 new high temperature records had been set for the region and Chicago had endured its worst heat wave death toll ever (adapted from The Weather by John Lynch).

Heat problems are not limited to city dwellers, of course. Everyone is vulnerable under the right conditions. Preventing heat illness or death depends on managing the six factors that lead to heat stress: temperature, humidity, air movement, ambient temperature, clothing and physical activity.

Heat stress occurs when the body core temperature gets too high for the normal internal mechanisms, sweating and blood circulation, to work effectively. Sweat has to evaporate to cool the body, so high humidity and light (or no) wind can bring on excessive sweating without cooling. Your body also circulates hot blood into peripheral areas to allow it to cool faster but if it’s hot outside as well, cooling doesn’t occur and the temperature of the blood rises. Even when sweating is cooling you effectively, dehydration can set in very quickly and that is the common killer for most otherwise healthy people.

When you become dehydrated, there are several warning signals (symptoms) that occur in a progression towards death. Up to a five percent loss of water, you feel thirsty, uncomfortable, tired and drained of energy. Your appetite disappears and you feel nauseous. From six to ten percent dehydrated, progressively, you get dizzy, tingling occurs in your limbs, your mouth gets dry and your skin takes on a blue tinge.

You have difficulty speaking and, eventually, you can’t walk. If you watch another person experience this, he or she will range from acting crazy to appearing drunk. A person can survive short periods at 25 percent dehydrated under cooler conditions, but above 90F, 15 percent dehydration is probably fatal. The solution is to get water into the victim pronto!

Heat stress has a progression of injury that ranges from discomfort to a life-threatening crisis.

Heat rash occurs in hot, humid environments and, while not dangerous, can be uncomfortable. Dry clothing and clean, dry skin will solve this problem quickly.

Heat cramps are most common in the legs and belly and occur when a person is sweating heavily and replacing water but not salt. The skin is hot and moist and the pulse is normal. Drinking lightly salted water and getting into the shade to rest can help but medical attention may be needed if the cramps persist.

Heat exhaustion occurs when the body temperature controls are overtaxed and the core temperature is rising rapidly. Symptoms include heavy sweating, intense thirst, cool, moist skin, weak and fast pulse, fatigue, weakness or dizziness. The victim must be cooled quickly. Get somewhere in the shade, loosen clothing, fan and pour cool water on him or her. Give the victim salted water if possible. Seek medical attention if symptoms persist or worsen.

Heat stroke can cause death very quickly and requires immediate medial attention. It occurs when the body has used up its supply of water and salt. Sweating stops and the whole body, including the brain, overheats rapidly. Symptoms include hot, dry, flushed skin, rapid pulse, difficulty breathing, confusion, weakness and nausea.

In early heat stroke stages, a person may still have cool, moist skin as they transition from heat exhaustion. Heat stroke victims can suffer seizures, convulsions, unconsciousness, and delirium. Seek medical help immediately and, while waiting,spray, sponge or immerse the victim in cool water (if possible) and give water. Do not try to give the victim water if they are unconscious; you could easily drown them!

Here are a few tips to help you avoid getting ill from the heat in the first place:

  1. Follow work/rest routines that keep you from getting exhausted in the heat. That is why people in hot climates move slowly and don’t try to do too much in the hottest parts of the day.
  2. Alternate heavy and light work or move from hot to cooler locations periodically. Take advantage of breaks to rest and get cool.
  3. Drink water often. Do not wait until you feel thirsty; you are already dehydrated by the time you feel the need for water. A loss of only 2.5 percent of your body water (roughly 2 quarts) will cause you to lose 25 percent of your work efficiency.
  4. Avoid caffeine and alcohol; both act as diuretics (they cause you to lose water).
  5. Eat regularly and lightly and, if you’re sweating a lot, add a little salt to your food (if you are on a salt-restricted diet, check with a doctor first). Salt tablets are not recommended.
  6. Take time to get used to the heat and slow down when you leave a cooler place and go somewhere hot. Most people can adapt within a few days but some never adjust. Even when you do adapt, air temperatures of 110F will cut your ability to work by 25 percent.
  7. Dress in cool, loose, comfortable clothing made of light fabrics and in light colors. Dress in layers so you can add or remove items as the temperature dictates. The more bare skin you expose, the greater your risk for heat problems is. This is because sweat wicks away (evaporates) from bare skin but wets clothing, which helps cool you longer.
  8. If you begin to experience symptoms of heat stress, react right away to keep it from getting worse. Use the buddy system, when you can, to watch out for each other; it’s often easier to recognize symptoms in someone else than in yourself.

Heat takes a vicious toll on anyone who fails to give it the respect it deserves. Dress wisely, drink plenty of water, work and travel in the cooler parts of the day whenever possible, and seek shelter when daytime heating is at its peak. Desert dwellers have known these rules for many generations and have survived heat conditions unimaginable to people from gentler climates. Take the lessons they have learned to heart and do what they have done for thousands of years: survive.

Written by Melody L. Higdon, 14 WS/DOPA (June 2003)