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Working with Gases
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The gases you will meet
Part of a plumber's work involves bottled gases, both flammable and non-flammable. Each one behaves differently, and the differences are what keep you safe. Every cylinder is colour coded, and the thread direction on the fittings tells you whether it is a fuel gas or not.
| Gas | Cylinder colour | Thread | What it is for |
|---|---|---|---|
| Propane | Red | Left hand | Soldering copper tube and fittings — the plumber's everyday gas |
| Butane | Blue | Left hand | The other bottled LPG. Indoor and portable work — it stops giving off gas in the cold |
| MAPP | Yellow | Left hand | Soldering, but a much hotter flame than propane |
| Acetylene | Maroon | Left hand | Welding and brazing, with oxygen. Plumbers mainly use it for lead welding |
| Oxygen | Black, white shoulders | Right hand | Used with acetylene to harden the flame and raise the temperature |
| Nitrogen | Grey, black shoulders | Right hand | Inert gas, used for pressure testing systems |
Why the threads differ. Fuel gases have left-hand threads and oxygen has a right-hand thread. It is a physical safeguard: you cannot connect a fuel gas fitting to an oxygen cylinder even if you try. The design removes the mistake rather than relying on you remembering.
LPG — propane and butane
LPG is the family name for a group of carbon-based flammable gases found in coal and oil deposits. The family includes methane, ethane, butane and propane, but only butane and propane are sold as bottled LPG.
- It is a colourless liquid that evaporates into gas in open air. One litre of liquid propane makes 250 litres of gas.
- It has no natural smell. A distinctive odour is added so you can detect a leak.
- It burns or explodes when mixed with air in the right ratio and met with a source of ignition.
- It is heavier than air. A leak sinks, flows a long way along the ground, and collects in drains, gullies, cellars and trenches.
The main risks are fire and explosion, carbon monoxide poisoning, asphyxiation and extreme cold burns.
Propane or butane? Propane boils at −42°C, butane at only −4°C. A bottle only gives gas if the liquid inside can boil, so on a cold morning a butane bottle can stop working while propane carries on. That is why propane is the site gas.
Acetylene and oxygen
Acetylene is colourless and odourless, though it smells of garlic when contaminated. Unlike LPG, acetylene is lighter than air and rises — so a leak gathers at high level rather than in the trench. Burned without oxygen it gives a sooty flame full of carbon.
Oxygen does not burn. It is a powerful oxidising agent, which means other materials burn fiercely in its presence. Never use oxyacetylene near jointing compounds or grease, and if you find oil or grease on a regulator or cylinder valve, do not use the equipment.
Never exceed 15 PSI of acetylene. Above that pressure acetylene becomes unstable and can ignite spontaneously or explode with no outside source of ignition. Normal working pressure is around 0.14 bar (2 PSI).
Transporting and storing cylinders
- Keep full cylinders separate from empty ones.
- Store oxygen at least 3 metres from acetylene or LPG, or separate them with a wall.
- Keep all cylinders away from combustible materials, sources of ignition, and corrosive, toxic or oxidising materials.
- Store on a hard surface in a secure, labelled, open-air compound — not on soft ground.
- Acetylene and LPG cylinders stay upright in use, in storage and in transport, even when empty. Secure anything stacked vertically so it cannot fall.
- Oxygen may be stacked horizontally, no more than four high, wedged so it cannot roll.
- Shield cylinders from direct sunlight and heat. Heat raises the internal pressure, which can force a leak or, in the extreme, burst the cylinder.
- Never lift a cylinder by its control valve, and never subject one to a shock or a fall.
- Move cylinders on a purpose-designed trolley made to BS 2718. A three-wheeled trolley is more stable than a two-wheeled one.
Checking heat producing equipment before use
A visual inspection is looking at the general condition of the kit and its freedom from obvious damage or leaks. On an oxyacetylene set, check that:
- Flashback arresters and non-return valves are fitted in both the oxygen and the acetylene lines, and are in good condition. One in the fuel line alone is not enough — a flame can travel back along either.
- Hoses are the correct colours — red for acetylene, blue for oxygen — with no wear or damage, as short as practicable, and not taped together.
- Regulators are the correct type for the gas, and the adjusting screw is undamaged.
- There is a bottle key in each bottle, so it can be shut off fast in an emergency.
- Bottles are chained securely to a sound trolley, with no damage to the bottles or valve assemblies.
Test every joint for leaks with leak detection fluid — never a naked flame, and never the smell of gas alone. Check the set at least annually, and take regulators out of service after five years.
Shutting down. Close the acetylene blowpipe valve first, then the oxygen. A flashback is the flame burning back inside the torch body, with a high-pitched whistle — usually caused by gas pressures that are too low, a hose leak, or a loose connection.
Before you light anything
You must be trained in the safe use of the equipment, the precautions to take, the right type of fire extinguisher, and the means of escape, raising the alarm and calling the fire brigade. Many companies run a written hot work permit covering what work is being done, how, when, and what precautions apply.