In a car parked in the sun on a 90-degree day, the temperature inside will reach 130 degrees within 15 minutes. Medical experts say that's hot enough to kill anyone -- adult or child -- who is inside long enough.

How long it takes to develop heat stroke -- an often fatal condition in which the victim's body temperature shoots to 106 or more -- depends on humidity, air circulation and the person's general health.

But in most reported cases of children dying in cars, parents said they left the child for between 30 and 60 minutes, according to Dr. Kenneth B. Roberts, associate chief of pediatries at Sinai Hospital in Baltimore.

Leaving a child shut in a parked car on a humid day is a setup for a tragedy, he said. "It's very much like an oven."

Roberts and his wife Ellen studied the risk of leaving children in cars in the summer of 1975, after the 1973 death of a 19-month-old left in a car in Annapolis. He said that in addition to finding that the temperatur inside peaks within 15 minutes, even with the window rolled down two inches, they discovered other risks. For instance, a dark-colored vinyl seat will be even hotter than the air, and will transfer heat to the child by conduction. b

Also, high humidity -- which reduces the amount of heat a person can lose by the evaporation of sweat -- becomes even more dangerous in a parked car with no air circulation.

Even a small breeze created by cracking a window would be no help to a toddler on the seat far below, he said.

To lose heat by sweating, "the air around needs to be able to accommodate the water," Roberts said. "A breeze helps because . . . new, dryer air comes in and takes away the water." But in a closed car, the air quickly becomes saturated. "You start dripping, but it doesn't do you any good."

Anyone trapped in a 130-degree chamber will eventually sweat enough to develop heat exhaustion, in which the victim develops symptons such as light-headedness, headache and vomiting because of fluid loss. If the suffer is not cooled down, heat exhaustion progresses to heat stroke, in which so much fluid has been lost tht the victim can no longer sweat. Then the core body temperature rises rapidly, and -- as one doctor put it -- "organs are getting fried."

Heatstroke is usully fatal unless the victim is treated immediately in a hospital with rapid cooling and fluids.

Under normal conditions, children (other than newborn babies) handle heat about as well as adults, according to Dr. Alan Fields, associate director of the intensive care unit at Children's Hospital National Medical center. But they don't handle sitting in closed cars as well.

A 3-year-old would not recognize the danger quickly enough to try to escape. Fields said.