The bouncy house seems like an innocuous childhood delight. What's not to love about a giant, inflatable room where kids can jump and scream in one safely contained location? The problem, recounted in a dubious study by a team of geographers and doctors, is that bouncy houses can cause heat stroke, especially this summer during our hottest year on record.

Researchers from the University of Georgia and the Dell Children’s Medical Center in Austin, Texas knew that bouncy castles caused an enormous number of injuries. But over the past 20 years, the numbers have skyrocketed. As the researchers write in a paper out today in Bulletin of the American Meteorological Society, "One of the most staggering findings is that during the period of 1995 to 2010, a 15-fold increase was observed in the rate and number of bounce house injuries (roughly 5.28 injuries per 100 000 children in the United States annually)." Staggering, indeed. Mostly these were fractures, strains, and "other injuries to the upper and lower extremities."

The researchers decided to find out whether heat stroke was another, hidden danger to be found in these funhouses of pain. Though they could find only one reported instance of heat stroke from a bouncy castle, they forged ahead with their quest. Last summer, they spent a single afternoon measuring the "air temperature, humidity, wind speed, and computed heat index values" inside a typical bouncy castle, which they inflated in a grassy plaza on the University of Georgia campus. What they discovered is that these puffy joy rooms are actually heat-trapping danger chambers:

Results show that maximum air temperatures in the bounce house can reach up to 3.7 C (6.7 F) greater than ambient conditions and peak heat index values may exceed outdoor conditions by 4.5 C (8.1 F). When considered in the context of the National Weather Service heat index safety categories, the bounce house reached the “danger” level in over half of the observations compared with only 7 percent of observations for ambient conditions.

Put simply, the Athens bouncy house reached a "danger" level heat index half the time, while the outside conditions only reached it 7 percent of the time. So even when the weather service hasn't issued a heat index warning, your bouncy house may be a heat stroke hazard for the people playing inside. At least, that's what the research team concluded--partly because the wind speed inside the empty bouncy castle was nil. They neglected to mention that actual bouncy houses usually have people jumping up and down inside, creating a lot of air rushing in and out.

Never fear, though. The researchers created a handy chart for people who are concerned about bouncy house temperature threats. As you can see (above), the chart predicts typical bouncy house heat indexes based on ambient temperature and humidity. Always check the chart before you start inflating.

Or, you know, do another study where you actually measure what happens in a typical bouncy castle. That would be good too.