Every summer in the United States, the issue of children being left unattended in motor vehicles hits the headlines. The stories often spur outrage and confusion over how such tragedies continue to occur, despite the media attention and persistent warnings to parents about how closed car windows trap heat, rapidly increasing interior temperatures.

The statistical patterns of child deaths related to heat stroke after being left in cars — also called “juvenile vehicular hyperthermia” — are not always easy to discern. The Centers for Disease Control and Prevention has provided occasional data on the issue, but systematic data are not currently available. Over the period 2000-2001, for example, the CDC found that although child injuries in and around parked motor vehicles (more than 9,000 over this period) result more frequently from other types of accidents, the most frequent cause of child death related to stationary cars (78 over that period) was indeed heat stroke.

Jan Null, a scientist at San Jose State University, has also been tracking such cases by aggregating news reports. He notes that, because of a lack of consistent medical categorization and record-keeping, even “efforts to track hyperthermia deaths of children in vehicles through death certificates miss perhaps as many as half of the cases.” Null estimates that 646 children in the United States have died in this fashion between 1998 and 2015, with states such as Texas, Florida and Arizona ranking high both in terms of aggregate and per capita incidents.

There have been few, if any, attempts to model this phenomenon scientifically to determine the conditions endured in a hot car for young children over precise intervals across all seasons. A 2015 study published in the journal Forensic Science, Medicine and Pathology, “Evaluating Infant Core Temperature Response in a Hot Car Using a Heat Balance Model,” seeks to fill that research gap by performing a year-round observational study in Texas on a vehicle and modeling predicted outcomes for an average 1-year-old male child.

The experimental data were obtained from the field in Texas; the vehicle was an “enclosed white station wagon with grey interior and nontinted windows” that “was parked in the same area and east-facing orientation of an asphalt parking lot on each day of data collection.” A child was never present in the car. The researchers — Andrew J. Grundstein of the University of Georgia; Sarah V. Duzinski and Sujit S. Iyer of Dell Children’s Medical Center; David Dolinak of the Travis County Medical Examiner’s Office (Tex.); and Null of San Jose State — took into account environmental variables such as air temperature, humidity, cloud cover and wind speed. All of this was used to estimate the impact on the physiology of a young child — accounting for variables such as clothing type and modeling the overall “energy budget” of the child — over four seasons.

The authors note that existing research literature suggests that “over half (50.5 %) of heat-related vehicular fatalities in the U.S. occurred when children were simply forgotten inside the vehicle by their caregiver (often on the way to work).” They also note that it is necessary to study this scientific phenomenon under all weather conditions: “The cabin of a stationary, unventilated vehicle with full sun exposure can reach dangerously high temperatures, even in cooler weather, due to a greenhouse effect.”

The study’s findings include:

• Temperature readings in the car were taken from 8 a.m. to 4 p.m. Depending on the season, the speed with which death would have theoretically taken place varied widely, but in all cases the model suggested mortality by 2 p.m., even in the colder months.
• When the starting temperature was 83 degrees Farenheit in August, the “model infant reached un-compensable heat within 20 minutes (by 8:20 a.m.), heat stroke within 105 minutes (by 9:45 a.m.), and demise within 125 minutes (by 10:05 a.m.).” Even in January, with a starting temperature of 35 degrees Farenheit, the model infant would reach “un-compensable heat within 140 minutes (by 10:20 a.m.), heat stroke within 315 minutes (by 1:15 p.m.), and demise within 355 minutes (by 1:55 p.m.).”
• Overall, “in spring and summer, if undiscovered, an infant left in a heating car would reach demise before lunchtime.”

“[T]hese findings represent a conservative estimate of an infant’s heat budget in an enclosed vehicle,” the researchers conclude. “Further, an infant could reach the thermal thresholds of un-compensable heat, heat stroke, and critical thermal maximum more quickly if they are already ill, medicated, immunocompromised, dehydrated, or overdressed for the weather conditions.”

Keywords: children, parenting, hot cars, child safety, child abuse, infant death, unattended children, overheated cars