The extreme heat has been breaking records all over Europe<\/span>Asia and North America<\/span>with millions of people sweltering in far above “normal” heat and humidity for days on end.<\/p>\n Death Valley<\/span> reaches a temperature of 128 degrees Fahrenheit<\/a> (53.3 degrees Celsius) on July 16 \u2013 not the world’s hottest day on record, but close. Phoenix hit a record heat streak with 19 straight days of temperatures above 110 F (43.3 C), accompanied by a long streak of nights that never dropped below 90 F (32.2 C), leaving little chance to people without air conditioning to cool off. Globally, Earth probably had one hottest week on modern record<\/span> at the beginning of July. <\/p>\n Heat waves are getting to overfeed<\/span> as the weather changes: it lasts longer, becomes more frequent and hotter. <\/p>\n A question many people ask is, “When will it become too hot for normal daily activity as we know it, even for young, healthy adults?” <\/p>\n The answer goes beyond the temperature you see on the thermometer. It’s also about humidity. Our<\/a> research<\/a> is designed to reach the combination of the two, measured as “wet bulb temperature”.<\/span> Together, heat and humidity put people at much greater risk, and the combination becomes dangerous at lower levels than scientists previously believed. <\/p>\n Scientists and other observers have been alarmed by the increasing frequency of extreme heat combined with high humidity. <\/p>\n In the Middle East, Asaluyeh, Iran, recorded an extremely dangerous situation maximum wet bulb temperature<\/a> of 92.7 F (33.7 C). July 16, 2023<\/a> – above our measured upper limit of human adaptability to humid heat. India and Pakistan have also come close. <\/p>\n People often point to study published in 2010<\/a> who theorized that a wet-bulb temperature of 95 F (35 C), equal to a temperature of 95 F at 100% humidity, or 115 F at 50% humidity, would be the upper limit of safety, plus beyond which the human body can no longer cool itself by evaporating sweat from the body’s surface to maintain a stable body temperature. <\/p>\n It was not until recently that this limit was tested in humans in laboratory settings. The results of these tests show even greater cause for concern. <\/p>\n To answer the question of “How hot is too hot?” we brought healthy young men and women to the Noll Laboratory at Penn State University to experience heat stress in a controlled environmental chamber. <\/p>\n These experiments provide insight into what combinations of temperature and humidity begin to be harmful to even the healthiest of humans. <\/p>\n S. Tony Wolf, a postdoctoral researcher in kinesiology at Penn State and co-author of this paper, conducts a heat test in the Noll lab as part of PSU’s Human Environmental Age Thresholds project.<\/span><\/p>\n <\/p>\n Patrick Mansell\/Penn State<\/p>\n <\/span><\/p>\n Each participant swallowed a small one telemetry tablet<\/a> who continuously monitored their deep or core body temperature. They then sat in an environmental chamber, moving just enough to simulate the minimal activities of daily living, such as showering, cooking and eating. The researchers slowly increased the temperature in the chamber or the humidity in hundreds of separate experiments and monitored when the subject’s core temperature began to rise. <\/p>\n This combination of temperature and humidity at which the person’s core temperature begins to rise continuously is called “critical environmental limit<\/a>.” <\/p>\n Below these limits, the body is able to maintain a relatively stable core temperature for long periods of time. Above these limits, the core temperature increases continuously and the risk of heat related illnesses<\/span> with prolonged exposures increases. <\/p>\n When the body overheats, the heart has to work harder to pump blood flow to the skin to dissipate the heat, and when you’re also sweating, this decreases body fluids. In the most severe case, it can lead to prolonged exposure heatstroke<\/span>a life-threatening problem that requires immediate and rapid cooling and medical treatment. <\/p>\n Our studies of healthy young men and women show that this upper environmental limit is even lower<\/a> than the theorized 35 C. It occurs at a wet bulb temperature of about 87 F (31 C) in a range of environments above 50% relative humidity. This would be equivalent to 87 F at 100% humidity or 100 F (38 C) at 60% humidity. <\/p>\n The limits of human adaptability <\/h2>\n
The PSU HEAT project <\/h2>\n
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