Acetylene C₂H₂
- 01Acetylene burns hotter with oxygen than any other common fuel gas — about 3,100 °C, hot enough to melt steel in seconds.
- 02It has the highest specific combustion energy of any common gaseous fuel: 11.93 kcal per gram.
- 03It cannot be stored as a compressed gas above roughly 1.5 bar — it would decompose. Every acetylene cylinder is really a sponge soaked in acetone.
- 04Before electricity reached most towns, acetylene lit them. Carbide lamps ran homes, bicycles, mines and lighthouses.
- 05It is one of the few gases that can explode with no oxygen present at all — it simply breaks apart into carbon and hydrogen.
Acetylene is lighter air (0.906×), boils at −83.6 °C (sublimes), and is flammable. See the product page →
Oxygen O₂
- 01Oxygen does not burn. Every fire you have ever seen was something else burning in it.
- 02It makes up 21% of air but 46% of the Earth's crust by weight — most of it locked in rock.
- 03Liquid oxygen is pale blue, and it is attracted by a magnet — which almost no other common liquid is.
- 04A cutting torch does not melt steel with its flame. The preheat starts the reaction, then a jet of pure oxygen burns the steel away.
- 05Under high pressure oxygen can set oil alight with no spark whatsoever, which is why greasy hands near a regulator are genuinely dangerous.
Oxygen is heavier air (1.105×), boils at −183.0 °C, and is an oxidiser. See the product page →
Nitrogen N₂
- 01Nitrogen is 78% of every breath you take, and your body does nothing with any of it.
- 02It is the most widely used industrial gas on Earth, almost entirely because it refuses to react with anything.
- 03One litre of liquid nitrogen becomes about 700 litres of gas as it warms — which is why a sealed flask of it bursts.
- 04It is why a packet of crisps is inflated: the nitrogen keeps the contents from going stale and stops them being crushed.
- 05Being odourless and painless makes it the quiet killer of industrial gases — there is no breathless warning before collapse.
Nitrogen is about the same weight as air (0.967×), boils at −195.8 °C, and is inert. See the product page →
Argon Ar
- 01Argon is named from the Greek for lazy, because it forms essentially no compounds with anything.
- 02It is the third most abundant gas in air at about 0.93% — more common than carbon dioxide.
- 03Almost all of it is a by-product: argon boils between nitrogen and oxygen, so separating those two produces it in the middle.
- 04It fills the cavity in double glazing because it conducts heat about a third less readily than air.
- 05Being 38% heavier than air, it silently pools in pits and tank bottoms — the main confined-space risk for welders.
Argon is heavier air (1.380×), boils at −185.8 °C, and is inert. See the product page →
Carbon dioxide CO₂
- 01CO₂ has no liquid state at normal atmospheric pressure — it goes straight from solid to gas, which is why dry ice smokes rather than melts.
- 02A CO₂ cylinder gauge reads full until it is nearly empty, because the contents are liquid under their own vapour pressure.
- 03It is the gas fire extinguishers are filled with, and also the gas that makes drinks fizz.
- 04Unlike nitrogen and argon it is physiologically active — around 5% in air causes headache and laboured breathing while plenty of oxygen remains.
- 05Being half again as heavy as air it collects at floor level, which is why beverage cellars need gas alarms.
Carbon dioxide is heavier air (1.529×), boils at −78.5 °C (sublimes), and is inert. See the product page →
Hydrogen H₂
- 01Hydrogen is the lightest element and makes up about 90% of all the atoms in the universe.
- 02It burns with an almost invisible flame — in daylight you may not see a hydrogen fire at all.
- 03It has the widest practical flammable range of the common industrial gases: 4% to 75% in air.
- 04It is about fourteen times lighter than air, so it rises and gathers at roof level rather than pooling.
- 05One Nm³ of hydrogen weighs just 90 grams — about the same as a small apple.
Hydrogen is lighter air (0.070×), boils at −252.9 °C, and is flammable. See the product page →
Helium He
- 01Helium was found on the Sun before it was found on Earth, discovered in sunlight during an 1868 eclipse.
- 02It has the lowest boiling point of any element, at −268.9 °C — under five degrees above absolute zero.
- 03It cannot be manufactured at industrial scale; all commercial helium is extracted from natural gas deposits.
- 04It is the only element that will not freeze solid at atmospheric pressure, no matter how cold it gets.
- 05Being inert and very light it leaks through materials that hold every other gas, which makes it the standard leak-detection tracer.
Helium is lighter air (0.138×), boils at −268.9 °C, and is inert. See the product page →
Nitrous oxide N₂O
- 01Nitrous oxide supports combustion much as oxygen does, so it demands the same no-oil discipline.
- 02It is one of very few gases with genuine medical, food and motorsport uses.
- 03In cream chargers it dissolves into the fat, then expands on release to whip the cream instantly.
- 04It is stored as a liquid under pressure, so like CO₂ it is sold by weight rather than by volume.
- 05Its nickname laughing gas dates from public demonstrations in the 1790s, decades before anyone used it for surgery.
Nitrous oxide is heavier air (1.530×), boils at −88.5 °C, and is an oxidiser. See the product page →
Compressed air Air
- 01Compressed air is not simply air in a bottle — breathing-quality air is a specified product with limits on oil, water, CO and CO₂.
- 02It is often called the fourth utility, after electricity, gas and water.
- 03Never substitute oxygen for compressed air: oxygen-saturated clothing ignites readily and burns faster than it can be removed.
- 04Grey with no neck band means air; grey with a black band means nitrogen. That single band is the whole difference.
- 05Compressing air heats it, and cooling it back down drops out water — which is why every serious compressed-air system has a dryer.
Compressed air is about the same weight as air (1.000×), boils at −194.3 °C, and is inert. See the product page →