How the wonderful world of gas detection affects banana production
Gas hazards can occur in some pretty unusual places, for example, the harvesting, shipping, storage and ripening of bananas is full of gas hazards.
Bananas are picked when they are cucumber green, but in order to ensure that they are not past their best when they finally arrive here, they are transported in a controlled atmosphere. This atmosphere is at a reduced temperature, but if the temperature gets too low then the banana will go mushy, so the ripening process is slowed down by replacing the oxygen present with carbon dioxide.
Carbon dioxide is colourless. At low concentrations the gas is odourless. However, at sufficiently high concentrations, it has a sharp, acidic odour. It is often thought of as primarily an asphyxiant, depleting the levels of oxygen and making the atmosphere unbreathable. However, CO2 is toxic in its own right and can have a damaging affect on health long before it would have displaced enough oxygen to asphyxiate someone. The symptoms of carbon dioxide poisoning at various concentrations are summarised below:
1% Drowsiness from prolonged exposure
2% Headache, laboured breathing, increases in blood pressure and reduced hearing
5% Headache, shortness of breath, dizziness, confusion, respiratory distress and panic attacks
8% loss of consciousness after 5-10mins, dimmed sight
10% Difficulty breathing, vomiting, hypertension. 2-3 minutes can lead to unconsciousness and be fatal
20% Exposure can cause convulsions and coma within 1 minute followed by death
Carbon dioxide has a long term workplace exposure limit of 5000 parts per million (0.5%).
Once the bananas reach their destination, they are ripened in specialised banana ripening plants. One of Europe’s largest such plants is near Coventry in the UK. Here the ripening process is controlled by adding ethylene to the atmosphere.
Ethylene is a colourless flammable gas with a faint "sweet and musky" odour when pure. It is the simplest hydrocarbon with a carbon-carbon double bond.
Ethylene occurs naturally when fruits ripen, and its presence triggers the ripening process, but ethylene is also highly explosive, with a lower explosive limit of just 2.4% by volume. Bananas also produce ethylene when they are ripening so a top tip for bringing a hard avocado to ripen is to place it with a ripe banana in a plastic bag.
Other fun facts about bananas
Bananas don’t grow on a tree. A banana plant is actually the world’s largest herb.
The banana comes from the same family as lilies, orchids and palms.
The central trunk isn’t a tree trunk - it’s a series of overlapping leaves, like a leek.
The fruits are curved because they bend to reach for the sun.
Bananas don’t have seeds. Every plant is a cutting from another. I’m not sure how the first one was grown in that case, that is a mystery, like how you grow seedless grapes.
So in order to safely deliver bananas to our supermarkets it is important to monitor for toxic levels of carbon dioxide and explosive levels of ethylene. Another example from the wonderful world of gas detection, and remember to make an atom split you need to use a high velocity neutron, to make a banana split you have to add whipped cream, ice cream and chopped nuts.