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What's heat index and can the temp outside let you cook an egg?

By NICK GARCIA Published Apr 18, 2023 7:38 pm

These days, Filipinos are probably channeling their inner Nelly singing his 2002 hit song Hot In Herre because of the scorching temperatures brought about by the dry season or, informally, "summer." The popular saying “It’s so hot you could fry an egg on the sidewalk" also comes to mind. (More on this later, on whether it's actually doable.)

The Philippine Geophysical and Astronomical Services Administration or PAGASA said the dry season will last until May.

Worse, the high temperatures during the period are being exacerbated by humidity, or the amount of moisture in the atmosphere. The higher the humidity, the more that there's that "nanlalangkit" feeling.

According to the National Geographic Encyclopedia, the air becomes clogged with much water vapor that there isn't room for much else. It will then be difficult to cool off because one's sweat can't evaporate into the air like it needs to.

The air temperature and relative humidity, then, accounts for heat index, or the level of heat or discomfort a person experiences.

In Daius in Bohol, PAGASA recorded an air temperature of 32.3C on April 17 at 2 p.m. But with a relative humidity of 76%, the heat index reached 44C, so much so that it's the supposed temperature the residents felt that day. (It's also PAGASA's highest computed heat index that day.)

This year, PAGASA's highest computed heat index was 49C in Guiuan, Eastern Samar last April 16 at 11 a.m.

Effect on the body

PAGASA has released a classification threshold, adapted from the United States' National Weather Service, on how the heat index can affect a person.

27C to 32C – Caution

  • Fatigue is possible with prolonged exposure and activity.
  • Continuing activity could lead to heat cramps.

32C to 41C – Extreme Caution

  • Heat cramps and heat exhaustion are possible.
  • Continuing activity could lead to heat stroke.

41C to 54C – Danger

  • Heat cramps and heat exhaustion are likely.
  • Heat stroke is probable with continued exposure.

54C and beyond – Extreme Danger

  • Heat stroke is imminent.
Prevention and treatment

In preventing heat-related illnesses (e.g. heat stroke) due to the high heat index these days, PAGASA has urged Filipinos to:

  • Limit the time spent outdoors
  • Drink plenty of water
  • Avoid tea, coffee, soda, and liquor
  • Wear umbrellas, hats, and sleeved clothing outdoors
  • Schedule heavy-duty activities for the beginning or end of the day when it's cooler.

But if emergency arises, PAGASA said one must observe the following:

  • Move the person to a shady spot and lie them down with legs elevated.
  • If conscious, have them sip cool water.
  • Remove clothing, apply cool water to the skin and provide ventilation.
  • Apply ice packs to the armpits, wrists, ankles, and groin.
  • Bring to a hospital immediately.
Cook an egg?

After all that's been said and done about heat index, does the saying "It’s so hot you could fry an egg on the sidewalk" actually make sense?

According to the United States Library of Congress, an egg needs a temperature of 70C (158F) to become firm. In order to cook, proteins in the egg must denature and coagulate, which won’t happen until the temperature rises enough to start and maintain the process.

With regards to the popular saying's "sidewalk," it is least likely doable. In the 2002 book What Einstein Told His Cook: Kitchen Science Explained, author Robert Wolke says sidewalk temperatures can vary depending on its composition, exposure to direct sunlight, and air temperature.

Wolke finds that sidewalks can only get up to 62.7C (145F), especially that they're mostly made concrete. Moreover, pavements are generally a poor conductor of heat, and with the absence or lack of additional heat source from below or the sides, the egg won't cook evenly.

Some people, apparently, were able to actually fry eggs on the hood of their cars as if it were a pan because it's made of metal. Others were also able to cook inside a closed car, on the dashboard, as if it were an oven.

The oven-like state inside also allows cooking more than just an egg. USA Today reported that Matt Standridge, chief meteorologist of the Arkansas-based KFSM-TV, was able to bake cinnamon rolls and cookies in his car, saying the dashboard reached 160F (71C). His baking lasted six hours.