Gas cutting is a critical skill applied in various Kenyan industries where precision metal cutting is required, such as in hospital equipment maintenance, school workshop repairs, or county government infrastructure projects. The ability to use gas cutting tools safely and effectively supports tasks ranging from routine fabrication work to emergency structural modifications. Understanding the tools, fuel gases, and their applications ensures professionals across sectors perform metal cutting with efficiency and safety.

3.1 Gas cutting tools and equipment

Gas cutting relies on specialised tools designed to direct and control a fuel gas and oxygen mixture to generate a flame capable of heating and cutting steel. The tools are engineered for precision, safety and ease of operation, which makes them indispensable in fabrication and repair workshops. A typical set consists of a cutting torch, hoses, regulators with pressure gauges, and flashback arrestors with check valves.

3.1.1 Cutting torch

The cutting torch is the primary tool used in gas cutting, combining fuel gas and oxygen to produce a flame that heats metal to its ignition temperature before the oxygen jet blows away the molten metal. It is designed to be ergonomic for handheld use and adjustable to suit various cutting requirements.

3.1.1.1 Use

The cutting torch is used to produce a controlled preheating flame and a separate stream of pure cutting oxygen. The operator sets the flame with the valves, selects a nozzle to suit the plate thickness, and then releases the cutting oxygen when the steel is hot enough. For example, a workshop cutting flat bar for metal furniture frames would fit a small nozzle and use a low gas setting so that the cut stays narrow and clean.

• Valve control: The torch body contains separate valves to regulate oxygen and fuel gas flow, allowing the operator to adjust the flame size and intensity depending on the metal thickness and cutting speed.
• Nozzle selection: Cutting nozzles come in various sizes and shapes to suit different applications, such as straight cuts, bevel cuts or shaped cuts. A larger nozzle delivers more heat and oxygen for thicker steel, while a smaller one suits thin plate.
• Preheating flame: The preheat valves are set to give a neutral flame, which heats the steel surface to a bright red before cutting begins. A flame that is too large wastes gas and melts the top edge of the cut.
• Cutting oxygen lever: Pressing the lever releases a high-speed jet of pure oxygen through the centre of the nozzle. The jet burns the hot steel and blows the molten oxide out of the cut, called the kerf.
• Lighting the torch: The torch is lit with a spark lighter held to the side of the nozzle, never with matches or a gas lighter, and the flame is then adjusted with the valves. This keeps the operator's hand clear of the flame and avoids burns.
• Handling during cutting: The torch is held with both hands where possible, at a steady angle and speed, so that the kerf stays even. The hoses are kept clear of the cut path and of falling sparks and hot slag.

3.1.1.2 Care

Care of the cutting torch keeps the gas passages clear, the valves leak-free, and the flame stable. A torch that is neglected may backfire, give a ragged flame, or leak gas at the valves. For example, a SACCO workshop that shares one torch among several welders should assign a daily check so that damage is found before the next user picks it up.

• Pre-use inspection: Inspect the torch before every use for damage or wear that could cause unsafe gas leaks. This matters most where several users share the same equipment.
• Tip cleaning: Regular cleaning of the torch tip prevents clogging from metal residues and slag. Use tip cleaners of the right size, not drill bits or nails, which enlarge and distort the nozzle holes.
• Leak checking: Check the hoses, connections and valves for leaks, for example by brushing soapy water on the joints and watching for bubbles. A leak is repaired before the torch is used again.
• Valve condition: Make sure the valves open and close smoothly, because stiff or worn valves make accurate flame control difficult. Valves that do not shut off fully must be repaired by a competent person.
• Keeping oxygen fittings clean: Oil, grease and dirty rags must be kept away from the torch and oxygen connections, because oil in contact with high-pressure oxygen can ignite. Hands and gloves should be free of grease when connecting the torch.
• Careful handling: Do not drop the torch or use it as a hammer or lever, as this bends the tubes and damages the seats inside the head.
• Storage: Store the torch in a dry, secure place to prevent corrosion and accidental damage. It should be disconnected or hung where its nozzle cannot be knocked.

Hoses

The hoses connect the cutting torch to the gas cylinders, carrying oxygen and fuel gas separately to the torch. They are colour-coded and built to withstand working pressure and to keep the two gases apart until they reach the torch.

Colour codes differ between makers and countries: some LPG hoses are orange, and some imported American equipment uses green for oxygen. Always read the marking on the hose before connecting it.

• Regular inspection: Hoses must be inspected regularly for cracks, leaks or brittleness, especially where they are exposed to sun, rain or hot slag.
• Tight connections: Connections between hoses and torch or cylinders should be tight and leak-free; loose fittings can cause dangerous gas leaks leading to fires or explosions.
• Suitable length: The length of hoses should suit the workspace; excessively long hoses tangle easily and are more likely to be damaged.
• No twists or kinks: Hoses must not be twisted or kinked, as this restricts gas flow and affects flame quality during cutting.
• Coiling and hanging: Coil and hang hoses after use to prevent deterioration and keep them clear of the floor and of vehicles.

Regulators and gauges

Regulators reduce the high cylinder pressure to a lower, steady delivery pressure for the cutting torch. Pressure gauges show the cylinder pressure and the delivery pressure, so the operator can set and monitor the gas supply.

• Steady delivery pressure: Regulators keep the delivery pressure steady at the set value, which protects the hoses and keeps the flame stable. Flashback is stopped by flashback arrestors and check valves, not by the regulator.
• Monitoring gas supply: For oxygen, the cylinder gauge reading shows how much gas remains, so cylinder changes can be planned. Acetylene and LPG contents cannot be judged reliably from pressure and are checked by weight.
• Calibration and maintenance: Regular checking and servicing of regulators keeps the pressure control accurate, preventing inconsistent flame performance during cutting.
• Leak checks: Check for leaks around regulator connections and replace worn seals.
• Correct installation: Fit regulators following the manufacturer's guidelines, using the regulator made for the gas in question, to avoid contamination and keep the system sound.

Flashback arrestors and check valves

Flashback arrestors and check valves are safety devices fitted on the torch, hoses or regulators to stop a flame travelling back into the hoses or cylinders, which could cause an explosion.

• Operator protection: These devices protect the operator and the gas supply if a flashback occurs, which is vital in garages and workshops where several cutting jobs run at once.
• Regular testing: Flashback arrestors must be inspected and tested regularly to ensure they function correctly.
• Flow direction: Check valves keep the gas flowing one way, reducing the risk of gases mixing in the hoses.
• Compliant installation: Devices must be compatible with the gas used and correctly positioned in the supply line, following the manufacturer's instructions.
• Prompt replacement: Replace flashback arrestors and check valves immediately if damage or malfunction appears during routine safety checks.

Chapter Summary

This chapter covered the essential tools and equipment used in gas cutting, focusing on the cutting torch, its proper use, and maintenance to ensure safety and efficiency. It then explored different types of fuel gases employed in gas cutting, explaining their specific applications for various cutting tasks. The preparation of steel materials up to 6 mm thickness was discussed, highlighting the importance of accurate measuring and marking out before cutting. The chapter also detailed the step-by-step gas cutting procedure for steel within this thickness range, emphasizing careful control of the torch and flame to achieve precise cuts. Finally, practical applications of gas cutting were examined, demonstrating how the process is applied in real-world metal fabrication and repair scenarios. Throughout, the chapter underscored the integration of proper technique, equipment care, and material preparation for effective gas cutting outcomes.