During July 1995, an infant in southeast Louisiana died as a result of heat exposure in an enclosed automobile. To evaluate degree of heat exposure in a vehicle, we compared the temperature rise inside an enclosed, dark-colored vehicle with the temperature rise in a light-colored vehicle with the windows partly open. Within 20 minutes, readings in both cars exceeded 125°F and reached approximately 140°F in 40 minutes--a temperature rise of over 45°F. A person who is unable to remove himself from an enclosed vehicle is at risk for a life-threatening crisis if left alone in a sun-exposed car for even a relatively short period of time.

When the body is exposed to extreme temperatures serious harm can occur. Although heat-related illness and death occur primarily among the elderly, infants are also at risk (1, 2) Heat exhaustion and heat stroke can occur rapidly in enclosed vehicles. During July 1995, a two-year-old child in southeast Louisiana died as a result of heat exposure in an enclosed automobile. In addition, two children under the age of five died in Louisiana during 1993 from heat exposure.

This study compares the temperature rise inside two vehicles exposed to sunlight.

Using a Labcraft 227-876 thermometer, we measured the increase in interior temperature of two cars exposed to the sun. Serial readings were taken every 10 minutes from 2:30 PM to 4:00 PM in downtown New Orleans on July 27, 1995. The outside ambient temperature was 93°F at the beginning and end of the testing process. The sky was partly cloudy and the relative humidity was reported by the US Weather Service as 53%. Car #1 was a dark-blue sedan with the windows closed. Car #2 was a light-gray minivan with both of the front windows open approximately 1.5 inches. The thermometer was in direct sunlight in Car #1 but was shaded from direct sunlight in Car #2. The thermometer was placed upon the front car seat to match the likely position of an occupant. The seats in both vehicles were cloth.

Within 20 minutes, readings in both cars exceeded 125°F and reached a maximum stabilized temperature in 40 minutes (Figure). The temperature rise in the first 10-minute interval was more severe for the dark-colored enclosed sedan than for the light-colored minivan. The maximum stabilized temperature was also higher for the dark enclosed sedan (140°F compared to 138°F), which was a temperature rise of over 45°F in less than 1 hour.

The combination of hot summer sun and carelessness can have devastating consequences. Attempts to add an element of safety "cracking" the windows enough to let in air but keep others out were demonstrated to be ineffective. The temperature readings for the light colored vehicle with partially open windows were much higher than previously reported. This may be because readings were taken at seat-level and during the summer season as opposed to the "pleasant autumn day" in one study (3) or about 6 inches from the ceiling in the other (4). The temperature rise and maximum stabilized temperature readings for the dark, enclosed sedan were similar to previously published studies (3, 4). As in other studies, we found that "cracking" the windows is an ineffective attempt to keep the car interior at an acceptable temperature.

Early recognition of heat illness is imperative. Heat exhaustion occurs when heat stress causes fluid depletion. The signs of heat exhaustion include profuse sweating, headache, dizziness, nausea, vomiting, muscle weakness, and visual disturbances. If left untreated, heat exhaustion can lead to heat stroke. Signs of heat stroke include: hot, dry skin, abnormally high fever, dehydration, and impaired mental status.

The primary causes of heat stroke vary with age. The most common cause of heat stroke in adults is strenuous exercise. Heat stroke in infants, however, is primarily associated with increased environmental temperature or poor fluid intake (2). Heat stroke occurs more readily in infants who are ill or have other predisposing conditions such as congenital nervous system abnormalities. However, healthy infants are also at risk for heat stroke. Studies show that infants in good health have been found to run a temperature over 101°F in a warm environment (5).

To maintain proper body temperature, heat load and heat dissipation (radiation, convection, and evaporation) must be balanced. In a warm climate most body heat is lost through evaporation. But, as the humidity rises, perspiration and evaporation become inefficient. This is especially true for infants because they are normally kept clothed and in cushioned seats, thus decreasing the amount of evaporative surface. Clothing, cushioned seats, and the location of an infant below window level reduces the amount of heat loss through convection and conduction.

Special precaution, therefore, should be taken with infants and small children during periods of high temperature and humidity. An infant should never be left unattended in a vehicle even if it is "just for a few minutes." A tragedy can occur when what was anticipated as "a few minutes" extends much longer because of an unexpectedly long check-out line, a forgotten item, or a distraction by a seldom-seen friend. Unsupervised, small children playing in or around automobiles can unknowingly trap themselves inside a vehicle and be unable to get out. While it may seem that leaving a child in a hot car is obviously inappropriate, the recent deaths are indications that the public isn't fully aware of the danger.

1 Danks DM, Webb DW, Allen J. Heat illness in Wants and children. Br Med J 1962;2:287-293.

2. Wadlington WB, Tucker AL Jr, Fly F. et al Heat stroke in infancy. Am J Dis Child 1976;130:1250 1251.

3. Roberts KB, Roberts EC. The automobile and heat stress. Pediatrics 1976;58: 101-104.

4. King K, Negus K, Vance JC. Heat stress in motor vehicles: a problem in infancy. Pediatrics 1991;68.

5 Carcullo HM. Sustained summer heat and fever in inants. J Pediatr 1949;35:24-42.

Ms. Gibbs is an epidemiologist with the Injury Control Section of the Louisiana Office of Public Health.

Mr. Lawrence is the supervisor of injury epidemiology with the Injury Control Section of the Office of Public Health

Dr. Kohn is the Medical Director of the Injury Control Section of the Office of Public Health.