Light the acetylene first, then add oxygen, and always follow your torch’s manual for pressure and tip settings.
For the full breakdown, see our best Acetylene Cutting Torch guide.
The safe way to use an acetylene cutting torch comes down to one fixed sequence: open the cylinders correctly, light the acetylene first, then add oxygen, and keep every pressure inside the manual’s limits. Skip any step and you’re risking flashback, fire, or an unstable gas supply. Here’s the procedure trained operators follow, step by step.
Setting Up An Acetylene Cutting Torch: Pressures, Valves, And Checks
A safe setup starts with the cylinders long before the torch is lit. Secure both tanks upright and away from heat, sparks, and oxidizers. Inspect every hose, fitting, tip, and gauge for damage, and keep oil and grease off all oxygen equipment—contaminated fittings can explode under pressure. Oregon OSHA’s acetylene safety guidance covers these storage and handling rules in detail.
Valve and regulator settings follow a strict order for a reason:
- Open the oxygen cylinder valve slowly and fully.
- Open the acetylene cylinder valve about 1/2 turn, but never more than 1 1/2 turns.
- Set regulator pressures to the manufacturer’s recommendation, keeping acetylene as low as possible and never above 15 psig.
- Purge each hose briefly before lighting, and purge again after any shutdown longer than 30 minutes.
| Setting | Value | Why It Matters |
|---|---|---|
| Acetylene regulator | Below 15 psig | Acetylene becomes unstable above this limit |
| Acetylene cylinder valve | 1/2 to 1 1/2 turns | Lets you close it quickly in an emergency |
| Oxygen cylinder valve | Slow and full | Avoids pressure shocks in the line |
| Torch acetylene valve | About 1/4 turn | The only valve you open before lighting |
| Hose purge | Brief, before use | Clears mixed gases from the lines |
| Ignition source | Spark igniter only | Matches and lighters cause flashback burns |
| Shutdown order | Acetylene, then oxygen | Prevents flashback into the hoses |
What Is The Correct Lighting Order?
Light the acetylene first, then bring in oxygen—never the reverse. Open the torch’s acetylene valve about 1/4 turn, hold the torch away from your body, and ignite the gas with a spark igniter. Once the acetylene is burning, slowly open the oxygen valve on the torch and adjust the flame until it settles into the neutral cone shape the job calls for. If the flame stays wrong at the recommended pressures, change the tip size instead of forcing the regulators past the manual’s numbers.
Cutting Technique And Common Mistakes
With the flame set, hold the torch so the inner cone sits just off the metal’s surface, preheat the edge until it glows cherry red, then squeeze the cutting lever and move steadily along the line. Keep the torch moving, never point it at people, cylinders, or combustibles, and never leave a lit torch unattended. Wear eye protection, gloves, long sleeves, and leather boots, and make sure nearby observers have the same protection.
The mistakes that injure people are almost always the same ones:
- Igniting with a lighter or matches instead of a spark igniter
- Exceeding 15 psig on the acetylene regulator
- Cutting drums or tanks that held flammables without an approved cleaning and gas-free procedure
- Skipping the fire watch or working without an extinguisher within reach
- Using one torch’s procedure on a different model without reading its manual
If you’re choosing a first rig rather than working with one you already own, our tested acetylene cutting torch roundup covers dependable models for a shop of any size.
The Shutdown Sequence That Prevents Flashback
When the cut is done, the closing order matters as much as the lighting order. Close the acetylene valve on the torch first, then the oxygen valve, then close both cylinder valves. Drain the lines by opening each torch valve until the gauges drop to zero, and back off the regulator adjusting screws to release spring tension.
If you leave the rig for more than half an hour, purge both hoses again before the next light. It takes ten seconds and clears any gas that may have accumulated while idle. These steps are standard practice across OSHA and NFPA hot-work guidance, and they keep flashback from becoming the last thing you learn about your equipment.
FAQs
Why can’t I use a lighter or matches to light a cutting torch?
Lighters and matches put your hand dangerously close to the flame zone and create an open flame that can ignite gas pooling from a slow valve. A spark igniter lights the acetylene at the tip from a distance, keeping your hand out of the line of fire and giving you a clean, immediate ignition source.
What happens if acetylene pressure goes above 15 psig?
Acetylene becomes unstable and can decompose explosively when it exceeds roughly 15 psig. That decomposition can propagate back through the hose to the cylinder even when the torch is working normally.
Can I cut a drum that once held fuel or solvent?
Only after the container has been thoroughly cleaned and certified gas-free under an approved procedure. Residual vapors inside a drum can ignite explosively when the torch touches the metal. Never assume a rinsed tank is safe; treat any container with a fuel history as hazardous until a formal inspection proves otherwise.
References & Sources
- Oregon OSHA. “Acetylene Safety.” Covers cylinder storage, pressure limits, and hot-work requirements for acetylene use.