18 Jan 2019

Death by Oxygen

by Adrienne Montgomerie
Flying high in the sky where the air is thin, fighter pilots wear oxygen masks to make sure they can breathe. But oxygen can be deadly. It's a tight balance.

Oxygen to Live

The air we breathe is actually mostly nitrogen (close to 4/5 of it). Only about 1/5 of the air outside is oxygen.* And what we breathe out still has quite a lot of oxygen in it. Our bodies only use about 1/4 of it.
We breathe O2: it has two atoms of oxygen in every molecule. Add an oxygen atom, and we get O3: ozone. High up in Earth's atmosphere, a thin layer of ozone protects us from too much harmful solar radiation (the UV in sunshine).

Oxygen to Kill

Oxygen is also used to clean water. The O3 of ozone quickly breaks down into O2. The free oxygen atom oxidizes cells and other pollutants in the water.
Oxidation happens when a substance joins with oxygen and turns into another substance. Rust is oxidation, so is an avocado turning brown. In cells, oxidation happens when oxygen burns through membranes and joins with the DNA inside.
Antioxidants prevent oxidation in cells, or at least slow it down. Vitamins C and E and others do this work, but with questionable results.

Can’t Live With It, Can’t Live Without It

When the air has less than 6% oxygen, humans can't get enough to live. But getting too much oxygen can be deadly too. When there's much more that 21% oxygen in the air, some of that oxygen binds to proteins in the lungs, interferes with the central nervous system, and messes with the eyes. It can lead to death. So doctors and nurses are very careful to not give patients too much.
Breathing is necessary, and oxidation is a natural process linked to aging. So, in some sense, oxygen will be the death of you.

*There's another 1% or so of outside air that is made up of carbon dioxide and argon (mostly), plus some other gases.

Photo courtesy of Defence Imagery, CC0 Pixabay.

4 Jan 2019

Humidex Shmumidex! It feels like what it is.

I often yell at the radio. I know it can’t hear me, but still. My most frequent rant is when the weatherperson says “The high will be 27 degrees, but with the humidex it will feel like 37 degrees”. And I retort “No it won’t. Because if the temperature were 37 degrees, you’d tell me that it feels like 58 degrees!” If every temperature “feels like” something different, we can never know what any temperature feels like!

 What’s happening is that the weatherperson is misrepresenting what the humidex is. The humidex isn’t an equivalent “feels like” temperature. The humidex isn’t a temperature at all. It’s purely a number.

This is what it means: 

Table 1
Degree of Comfort
some discomfort
great discomfort; avoid exertion
above 45
dangerous; heat stroke possible

Unfortunately, the numbers on the Humidex scale are close to temperatures in Celcius, so people confuse them. The Humidex was invented by Canadian scientists in 1962. 

I’d like to believe that scientists learned from this mistake. The UV Index (a measurement of Ultra-violet radiation), invented in 1992 – also in Canada, and then adopted by the World Health Organization – has a scale from 0 to 11+. Hard to confuse that with summer temperatures! 

Back to the Humidex: it's a useful indicator of health risks. Our bodies need to be within a remarkably small range of temperatures. “Normal” body temperature is about 37°C. If your temperature rises to about 40°C, you start having hyperthermia, which can be fatal. (Seventy people died in Quebec last summer because of a heat wave, and hundreds die of heat stroke each year in the U.S.A.).

Our bodies stay cool by moisture evaporating on our skin. Turning liquid into vapour requires heat energy which is taken from our bodies, cooling us down. When the relative humidity is high, evaporation is slower, so our cooling mechanism doesn’t work as well. That means we need to be careful not to generate too much internal heat from exertion. We also have to make sure we keep drinking, to allow moisture to be generated on our skin.

The Occupational Health Clinics for Ontario Workers Inc. created more precise humidex-based quidelines for work environments. These are recommended actions for employers, based on whether workers are acclimatized to heat, and whether they are doing light or heavy work. 

Wind Chill

Wind chill calculation is another Canadian innovation. In contrast with the Humidex, wind chill is specified in degrees. When a body (like a human body, or a building) is warmer than the surrounding temperature, it loses heat to its surroundings. The bigger the temperature difference, the more quickly it cools. It loses heat more quickly when air is being blown past it. That’s why blowing on your soup or coffee cools it more quickly. Wind chill (for a specific temperature and wind speed) is the temperature which, without air movement, would cool a body at the same rate. So it’s quite accurate for a weatherperson to say something like “it’s 2 degrees, but with wind chill it feels like -7”.


I love hot weather and hate cold weather. So it's a small consolation to me that during winter, at least I don't have to listen to a weatherperson mangling what the numbers mean.