68 dead in Ballia amid heatwave: How high temperatures combined with high humidity can be fatal

High temperatures alone aren’t fatal in nature. It’s when high temperatures are combined with high humidity, known as the wet bulb temperature, heatwaves become lethal. For instance, in April this year, 13 people died from an apparent heatstroke while attending a government award function in an open space in Navi Mumbai. Although the city wasn’t experiencing heatwave conditions — the maximum temperatures were in the range between 30 and 35 degree Celsius — experts said high humidity levels at the venue could have been one of the reasons behind the unusual death toll.

The deaths in Ballia might have happened due to a similar reason. As per IMD, the relative humidity in the city on June 18 was 31 per cent (at 5:30 pm) and the maximum temperature reached 43.5 degrees Celsius. This means that the Heat Index (HI), or “real feel” temperature, touched 51 degree Celsius according to the calculations of the National Oceanic and Atmospheric Administration’s (NOAA) HI calculator. Such conditions could severely impact human bodies, sometimes leading to death. Notably, relative humidity levels of Ballia before June 18 weren’t available.

How can high temperatures and high humidity impact humans?

Experts suggest that high temperatures along with high humidity are dangerous for a reason.

Joy Merwin Monteiro, assistant professor at Indian Institute of Science Education and Research (IISER), Pune, in a column for The Indian Express, explained: “Humans lose heat generated within their bodies by producing sweat that evaporates on the skin. The cooling effect of this evaporation is essential in maintaining a stable body temperature.”

“As humidity rises, sweat does not evaporate —just like clothes take a long time to dry in humid locations – and makes it difficult to regulate body temperature. And this could cause a heat stroke, which takes place only when the body temperature goes above 40 degrees Celsius.”

What happens is that excessive heat increases metabolic activity in the body, leading to a drop in blood pressure and oxygen levels with increased sweating — this is a condition called hypoxia.

In an earlier report by The Indian Express, Dr Anoop Misra, executive chairman, Fortis Centre for Diabetes and Allied Specialties, was quoted as saying: “Metabolism goes haywire (in such conditions), creating a toxin overload which affects multiple organs… At that stage, things are extremely difficult to manage outside ICU care.”

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The report also pointed out that prolonged exposure to even moderate heat, with poor nutrition and hydration levels in these circumstances, can lead to hypoxia. Those with pre-existing metabolic disorders like diabetes, the obese or the elderly, are more vulnerable.