Carbon monoxide as a toxic gas

Follow the gas: from the flame to the cell

Step through all five stages. Each one is the reason the next one happens.

1. 1Burning with too little oxygenA fuel burning properly has enough oxygen to turn all its carbon into carbon dioxide. Here there isn't enough, so the burning is incomplete.+
2. 2Carbon monoxide formsIncomplete combustion makes carbon monoxide, together with soot (carbon particulates). Water is produced as well.+
3. 3No warningCarbon monoxide is very difficult to detect, so it can fill a room without anyone knowing.+
4. 4Into the bloodBreathed in, the gas diffuses into the blood and binds with haemoglobin in red blood cells instead of oxygen.+
5. 5Cells go without oxygenOxygen is no longer carried to the respiring cells. Fainting, coma and even death can follow.+

Commit before you look

Think about the carbon in the fuel. It can't all become carbon dioxide.

A boiler burns its fuel without enough oxygen to turn all the carbon into carbon dioxide. What forms instead?

What you need to know

• Burning a fuel with too little oxygen is incomplete combustion: not enough oxygen to turn all the carbon into carbon dioxide.
• Incomplete combustion makes carbon monoxide and soot (carbon particulates), with water also produced.
• Have a goFinish the sentence: combustion is 'incomplete' because there isn't enough oxygen to turn all the ___ into carbon dioxide.

  Carbon.

  Carbon in the fuel is what ends up as carbon monoxide or soot when oxygen runs short.

• Carbon monoxide is colourless and odourless, so it is very difficult to detect.
• Have a goYour mate says, 'I'd smell a gas leak, so I'd be fine.' Which fact you've just met proves them wrong?

  Carbon monoxide is odourless (and colourless), so it is very difficult to detect.

  A smell can only warn you if the gas has one, and this one doesn't.

• Breathed in, it diffuses into the blood and binds with haemoglobin in red blood cells instead of oxygen.
• Oxygen is then no longer carried to the respiring cells.
• Fainting, coma and even death can follow.
• Have a goCause or consequence? (1) cells going without oxygen, (2) someone fainting. Which one is behind the other?

  (1) is the cause and (2) is the consequence.

  The harm to the person comes last in the route; it happens because the cells go without oxygen.

• A carbon monoxide detector beside a heater or boiler detects the gas if it is present and alerts people.
• The device can then be serviced and fixed, so it burns its fuel by complete combustion rather than incomplete combustion.

The big picture

Burning a fuel with too little oxygen makes carbon monoxide. It is colourless and odourless, so it is very difficult to detect. It binds with haemoglobin instead of oxygen, so oxygen no longer reaches respiring cells, and fainting, coma or death can follow. A detector plus a serviced device is the defence.

⚠ Watch out

Stopping at 'carbon monoxide is toxic'. That names the danger without explaining it. Say how: it binds with haemoglobin instead of oxygen, so oxygen no longer reaches the respiring cells.

Memory hook

Starved flame, silent gas, starved cells. Detect it, then fix the flame.

Check yourself

Cover the page and tell the story out loud: what happens at the flame, why nobody notices, what the gas does in the blood, and what the detector and the service each do.