Why smog kills

City living and dirty air go together. But when it turns into a killer it's no longer just a vague inconvenience.

Sapa reports that deaths in Moscow are now averaging 700 a day. The city is experiencing its worst ever heat wave which, combined with the smoke from up to 40 wildfires raging to the south of the city, has resulted in a poisonous smog. The deadly smog, which has been blanketing the city for six days, is showing no signs of dispersing.

It brings to mind the deadly smog that enfolded London for four days in December 1952. No one thought anything of it until afterwards, when hospital reports indicated that 4 000 people had died from respiratory complaints. More recent research indicates that the number could have been as high as 12 000. More than 100 000 people became ill.

Why is air pollution so dangerous?
Smoke from fires causes high concentrations of carbon monoxide (CO, also known as the odourless 'suicide gas'). So do motor vehicle exhaust gases, as the residents of smog-plagued Beijing can attest. Traffic also emits nitrogen oxides (you can smell and see these – they’re a big part of ‘brown haze’); particulates (tiny airborne solids and liquids - the bigger ones add to haze, but the smaller ones penetrate deep into our respiratory systems); and hydrocarbons such as the carcinogen benzene. Hydrocarbons and nitrogen dioxide combine in the presence of sunlight to form ground-level ozone (the ‘bad’ ozone), a major component of smog.

But main offender is carbon monoxide. This gas has caused more accidental deaths than any other poison in history – not just because it’s deadly, but because it slips under the radar of the human senses: you can’t see, smell or taste it, and it doesn’t irritate the skin or mucous membranes.

And it’s fast-acting. By the time you notice symptoms of poisoning while indoors, it’s often too late.

Symptoms of carbon monoxide poisoning
Low levels of CO poisoning are often mistaken for those of other common ailments, such as ‘flu, and may include: headache, dizziness, nausea, fatigue, weakness and shortness of breath. You can strongly suspect CO poisoning if these symptoms improve when you get into fresh air.

With higher levels of poisoning, symptoms become more severe, and include worsening headaches, vomiting, fainting, confusion and impaired vision and hearing.

At very high levels, CO causes loss of consciousness, coma and eventually death.

Symptoms can occur within minutes of exposure to the gas, and you can succumb to its effects before you’re able to seek fresh air and safety. People who are sleeping or intoxicated can die from CO poisoning even more easily, especially if they are in enclosed spaces.

Who is most at risk?

Unborn babies, infants, and people with anaemia or a history of heart or respiratory disease are especially susceptible to the effects of concentrated CO exposure. Breathing low levels of the gas can cause increased chest pain and fatigue in people with chronic heart disease. Even healthy people who survive breathing high levels of CO can be left with permanent heart or brain damage.

Most at risk from air pollution in big cities are all people who have respiratory ailments such as asthma, lung infections, or emphysema, as well as the very young and the very old.

Mostly, staying indoors is safer, except when the pollution becomes so bad that indoor air is no cleaner than that outside. Many people wear face masks when going outside, which should make a difference. But there is only so much you can do. Many people are actually fleeing Moscow at the moment.

Common carbon monoxide sources
Carbon monoxide is produced as a result of the incomplete combustion of any carbon-based fuel (petroleum, gas, paraffin, oil, coal, wood, charcoal, etc).

Combustion produces other toxins too, but none as lethal as CO. When people die of smoke inhalation during fires, it is again CO that is the primary killer.

In the home, potential sources of dangerous CO levels include motor vehicle exhaust fumes, and the combustion fumes from fuel-burning appliances – such as charcoal braai grills, camping stoves, fireplaces, gas stoves and heaters, wood and coal ovens, and petrol generators and power tools.

When these appliances are kept in good working order and used correctly with sufficient ventilation, they don’t carry a high risk for CO poisoning. But faulty appliances used in enclosed (or even semi-enclosed) spaces, for example a charcoal braai grill burning in the kitchen or a car engine running in a closed garage, can cause CO to build up to fatal levels.

For the moment, though, the best the residents of Moscow can hope for is rain and wind – in that order. The rain to kill all the fires and the wind to clear the air.

(Susan Erasmus, Olivia Rose-Innes, Health24, Sapa, August 2010)

Carbon monoxide kills in minutes

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