Lighting, Flame Adjustment, and Safe Shutdown

Lighting, Flame Adjustment, and Safe Shutdown

Why This Lesson Matters

Oxy-fuel cutting is one of the oldest and most productive processes in the trade. A correctly adjusted flame cuts clean and fast; a wrong flame wastes gas, damages base metal, or creates a fire hazard. An incorrect shutdown can leave pressurized gas in hoses or allow backfire and flashback—both life-threatening events. Every step in this lesson is built on procedures recognized by AWS, NCCER, and the Compressed Gas Association (CGA).

---

Personal Protective Equipment Before You Touch Anything

Before approaching the outfit, confirm:

• Shade 5 welding goggles or cutting goggles — cutting produces intense visible and infrared light.
• Leather gloves — protect against sparks and hot metal.
• Leather or flame-resistant jacket and long pants — no synthetic fabrics that melt.
• Leather boots, steel-toed preferred — hot slag falls down.
• Fire extinguisher within arm's reach and a fire watch bucket (dry sand or water, depending on shop policy) are required at the station before any flame is struck.

Remove all flammable materials from the work area. Check that hoses are not kinked or draped over hot surfaces.

---

The Oxy-Acetylene Outfit: A Quick Orientation

The outfit consists of two cylinders (oxygen and fuel gas), two regulators, color-coded hoses (green or black for oxygen, red for fuel gas), and a torch body with a cutting attachment. Acetylene is the most common fuel gas for structural work because of its high flame temperature. Never use acetylene at pressures above 15 psi—acetylene becomes unstable above that pressure and can detonate inside the hose.

---

Lighting Sequence

Follow these steps in order every time:

1. Inspect hoses, connections, tip, and work area.

2. Open the cylinder valves: oxygen cylinder valve fully open (back-seat it); acetylene cylinder valve one to one-and-a-half turns only so it can be closed quickly in an emergency.

3. Set working pressures at the regulators per the tip manufacturer's chart (typical cutting tip pressures are in the low single-digit to low double-digit psi range for acetylene, and higher for oxygen—always follow the chart for your specific tip size).

4. Open the fuel gas needle valve on the torch a fraction of a turn.

5. Ignite with a flint striker only—never a cigarette lighter or matches. A lighter held near the tip can burn your hand; matches require two hands and delay safe control.

6. Adjust the fuel flow until the flame lifts slightly from the tip, then reduce it just until the flame settles back. This prevents a sooty, over-rich start.

7. Slowly open the oxygen valve on the torch. The flame will change character as oxygen is added—this is where flame adjustment begins.

---

Flame Types: Recognizing and Adjusting

Three flame types exist, and only one is correct for most cutting:

Carburizing (Reducing) Flame

• Identified by a white feather or streamer extending beyond the inner cone.
• Excess fuel gas; insufficient oxygen.
• Too much carbon is introduced into the metal—harmful for most steel cutting.

Neutral Flame ✓ Correct for cutting

• Sharp, well-defined blue-white inner cone with no feather.
• Oxygen-to-fuel ratio is balanced.
• Produces clean cuts with minimal oxidation of surrounding metal.
• To achieve it: after lighting on fuel gas alone, add oxygen gradually until the feather disappears and the inner cone becomes sharp and defined.

Oxidizing Flame

• Inner cone is shorter and more pointed than neutral; a slight hissing sound.
• Excess oxygen; the flame oxidizes (burns) the base metal excessively.
• Recognizable by a louder, more harsh sound and a visibly shortened, pinched cone.

Practice target: You must reach a neutral flame within 60 seconds of lighting on three consecutive attempts to pass the station check.

---

Safe Shutdown Sequence

This sequence prevents hose fires and backfire:

1. Close the cutting oxygen lever (if cutting was in progress).

2. Close the oxygen preheat valve on the torch first — this prevents fuel gas from burning back into the oxygen system.

3. Close the fuel gas valve on the torch.

4. Close the fuel gas cylinder valve at the cylinder.

5. Close the oxygen cylinder valve at the cylinder.

6. Open the fuel gas torch valve to bleed residual pressure from the hose; watch the regulator gauge drop to zero; close the torch valve.

7. Open the oxygen torch valve to bleed the oxygen hose; watch the gauge drop to zero; close the torch valve.

8. Back out (loosen) both regulator adjusting screws until they turn freely — this releases spring tension and protects the diaphragm.

Memorize the logic: oxygen preheat off first, fuel gas off second at the torch — the opposite order risks a backfire inside the tip.

---

Backfire and Flashback: Know the Difference

• Backfire: flame goes out with a pop; usually caused by touching the tip to the work or momentary pressure irregularity. Corrective action: close valves, let tip cool, relight.
• Flashback: flame burns back inside the hose toward the cylinder — very dangerous. Signs: squealing or hissing sound inside the hose, possible hose heating. Immediately close both torch valves, then both cylinder valves. Do not use the outfit again until a qualified person inspects it. Flashback arrestors installed on both hoses and at both regulators are required by good shop practice and strongly recommended by CGA guidelines.

---

Work Habits That Prevent Incidents

• Always use a striker — no exceptions.
• Never lay a lit torch down; hang it or hold it.
• Keep the tip pointed away from people, hoses, and cylinders.
• Never use oxygen to blow dust off clothing or work — oxygen-enriched clothing ignites violently.
• Report any hose that smells of gas after shutdown to your instructor immediately.