I read stuff like this on HN and think that many of you must be living in a different physical reality.

Why? 15 min is a bit of an artistic stretch, but otherwise the statement above is correct. 35C at 80% humidity means wet bulb temperature of 32 degrees, which is not survivable by most humans. 38C at 80% humidity means TW of 35 degrees, which is not survivable by anyone.

I totally agree that's correct except for key qualifying statement.

It is when people who don't have any real understanding of physics or biology make absurd comments.

Reminds me of the comment that a 40 MPH car crash isn't potentially deadly: https://news.ycombinator.com/item?id=26470848

I live in Greece where currently we're in the middle of a heatwave (temperatures above 38C for more than a week). I don't recall a single time in my life where we had high temperatures and high humidity levels. But I've read once that if the temperature is higher than 35C and the humidity above 60% you can't live outside because the body can't expel heat fast enough.

Here's the science behind this claim: https://advances.sciencemag.org/content/6/19/eaaw1838

> While some heat-humidity impacts can be avoided through acclimation and behavioral adaptation (12), there exists an upper limit for survivability under sustained exposure, even with idealized conditions of perfect health, total inactivity, full shade, absence of clothing, and unlimited drinking water (9, 10). A normal internal human body temperature of 36.8° ± 0.5°C requires skin temperatures of around 35°C to maintain a gradient directing heat outward from the core (10, 13). Once the air (dry-bulb) temperature (T) rises above this threshold, metabolic heat can only be shed via sweat-based latent cooling, and at TW exceeding about 35°C, this cooling mechanism loses its effectiveness altogether. Because the ideal physiological and behavioral assumptions are almost never met, severe mortality and morbidity impacts typically occur at much lower values—for example, regions affected by the deadly 2003 European and 2010 Russian heat waves experienced TW values no greater than 28°C (fig. S1). In the literature to date, there have been no observational reports of TW exceeding 35°C and few reports exceeding 33°C (9, 11, 14, 15). The awareness of a physiological limit has prompted modeling studies to ask how soon it may be crossed. Results suggest that, under the business-as-usual RCP8.5 emissions scenario, TW could regularly exceed 35°C in parts of South Asia and the Middle East by the third quarter of the 21st century (14–16).

> But I've read once

It's best not to assume what you read on the internet is always true. Some people post things that turn out to be utter nonsense. Easily checkable nonsense to boot.

It's explained further down in the comments. It's the so called wet bulb temperature. I was wrong about the 15 minutes limit though, turns out it's about two hours.

You'll be shocked to learn about steam rooms.

I believe that steam rooms are incompatible with human life in the sense that you will overheat and eventually in a hot steam room. Most people are sensible and exit before this happens.

And, like, the entire American south

In fairness it was air conditioning that turned Florida into useless swamp to tourist paradise/trap.

I really hate it because I know it will only make things worse long term but my North European country is rapidly installing AC everywhere now thanks to increasing heatwaves.

A great positive feedback loop, no? Anthropogenic Climate Change (ACC) creates a need for more AC which in turn creates more ACC which furthers the need for more AC. Yeah I don't see this going well for the next few decades.

I've been in steam rooms. You're strongly advised to stay no longer than twenty minutes inside.

95F at 80% humidity is typical summer weather in the southeastern US (though it's been much cooler this year). Is it comfortable? No, but it's also not death in 15 minutes.

Where does it get 95° F and 80% humidity in the southeastern US? I grew up in Miami, and it was rare to have a day above 90° F in the summer, but the humidity made it unbearable.

I can’t even imagine how hot it would have felt at 95° F or higher with the same humidity—I wouldn’t be surprised if it was deadly.

Which part? I think it gets grosser near the Redlands since you get the mugginess of the glades + less cooling from the ocean. Late July through early August can stabilize around 95, maybe 20% of the days were like that when I lived in Homestead, FL. The other days around that time like 85-92 F w/ 80% humidity.

But I guess you're right -- I've had friends heat stroke after 2-3 hrs of unshaded exposure when it hits ~92+ i.e. soccer pickup games. Shade will carry you a long way, even without AC though -- I have extended family in La Guajira that still lives like this.

Ah, yeah, I can totally see that. I grew up in the South Miami / Coral Gables / Coconut Grove areas...divorced parents so I was all over the place. I did always consider Homestead to be a sweltering swamp with desert heat. Going out there in the summer was always a nice way to get dripping with sweat. :P

> But I guess you're right -- I've had friends heat stroke after 2-3 hrs of unshaded exposure when it hits ~92+ i.e. soccer pickup games. Shade will carry you a long way, even without AC though -- I have extended family in La Guajira that still lives like this.

Oof...yep, same experience, especially when the sun isn't occluded by clouds. It's gnarly.

Cities near the coast are usually more moderate. New Orleans is a counter example that I've been to though. But, look at cities like Columbia, SC or Atlanta, GA. Very high humidity and very high day time temps in July and August.

Tampa dude... Tampa... east coast FL is typically nicer in climate compared to Gulf Coast. I grew up Gulf Coast, I live on the east coast now. Sooooooooooooo much nicer.

That's surprising to me! I always thought Tampa was more temperature than the east coast.

Houston.

Just as the OP said, these temperatures are deadly.

From https://www.houstontx.gov/health/Epidemiology/e-heat-illness....:

> In the summer of 2000, 26 deaths involving Houston residents were reported. In 2001, 13 deaths were due to heat.

From https://environmenttexas.org/news/txe/global-warming-increas...:

> Thursday, September 6, 2007, HOUSTON – The death toll from extreme heat in Houston each summer will increase from about 24 to nearly 32, resulting in 192 additional heat-related deaths by mid-century

> Just as the OP said, these temperatures are deadly.

> > Thursday, September 6, 2007, HOUSTON – The death toll from extreme heat in Houston each summer will increase from about 24 to nearly 32

The actual number of heat deaths in Houston and Harris County in 2018 was 15; Houston itself sees 4–6 per year. Maybe air conditioning is more common a decade later than was originally predicted, or perhaps medical intervention arrives more quickly or is more effective.

Sources: https://nihhis.cpo.noaa.gov/Urban-Heat-Island-Mapping/Campai... and https://www.houstonpublicmedia.org/articles/news/in-depth/20...

I think the problem with the OP is they said it 'means death'. Can be deadly would be better phrasing, particularly to those who are susceptible.

The reason why I think this distinction is important is because there is some level of heat + humidity where it really does mean death to anyone in some short amount of time.

Atlanta?

Who knew that saunas are actually death chambers...

They are, but not in 15 mintues - it's more like a few hours. But a human being can't survive for extended periods of time in a sauna.

A sauna has extremely low humidity. A steam room, on the other hand..

Not quite. There are dry saunas. And wet saunas. And everything in between. And then there are steam rooms. They are different things.

Sauna are dry. The wet ones are hammam.

Laughs in slavic banya.

You soft western babies with your dry saunas. Over there the banya is kept at 110% humidity, and old men beat you with sticks the whole time.

Completely false. Traditional authentic Finnish (where sauna was invented) sauna is wet. Dry sauna is some weird American concoction.

This is not in line with the traditional sauna definition.

this is so common in coastal places in Southern India. no death in 15mins here.

I can easily stay 15 minutes in a hammam. That is > 40°C and > 95% humidity. I think I have sometimes reached 30 minutes

4 million people in Houston would beg to differ.

I’m sure there are many other places as well.

My family and I were outside in above 35C and 80% humidity for over 8 hours two weeks ago and everyone was fine. Lots of walking etc with no issues.

No it doesn’t, that was pretty much the weather in Boston on Monday. It was pretty dreadful being out in it, but not deadly.

Do you have a source on this please?

They're confusing it with a 35 C wet bulb temperature. 35 C dry bulb temperature would only equal 35 C wet bulb temperature at 100% RH.

You can convert with a psychrometric chart [1] or with a calculator [2]. At sea level, 35 C dry bulb, 80% humidity is about 32 C wet bulb. Dangerously hot, yes, but it won't kill you in 15 minutes.

[1] https://upload.wikimedia.org/wikipedia/commons/9/9d/Psychrom...

[2] https://www.omnicalculator.com/physics/wet-bulb

It's the wet bulb thermometer reading (temperature read by a thermometer covered in water-soaked cloth over which air is passed). At 35°C it is considered lethal for humans after a couple of hours.

> Wet bulb thermometer readings are significantly lower than the more familiar dry bulb readings, which do not take humidity into account. Researchers say that at a wet bulb reading of 35C, the body can no longer cool itself by sweating and such a temperature can be fatal in a few hours, even to the fittest people.

https://www.telegraph.co.uk/global-health/climate-and-people...

Then as a Basque I would die on some heat waves in August happening every decade or so.

Crazy that steam rooms exist then…