LaserCanvas
Fire: the risk people underestimate
A laser cuts by burning, so small flames are normal and a sustained one is not. The common causes are debris under the work, too many slow passes, no air assist and an unattended machine. Keep a CO2 extinguisher and a fire blanket within reach, clean the bed, and stay in the room.
Normal flare versus a fire
A small flame that follows the head and goes out immediately behind it is the material burning where the beam is — that is how cutting works. What matters is whether it stays lit after the head has moved on.
- Flame travels along the kerf behind the head — stop the job.
- Flame persists in one spot after the head leaves — stop the job.
- Flame in the debris tray, not at the cut — stop the job and expect it to be worse than it looks.
What actually starts them
| Cause | Why | Fix |
|---|---|---|
| Debris under the work | Offcuts and dust in the bed catch and burn unseen | Clean the bed between jobs; vacuum the honeycomb |
| Too many slow passes | Heat accumulates faster than it dissipates | Fewer, faster passes at higher power |
| No air assist | Nothing blows the flame off the surface | Run air assist on anything organic |
| Cutting the wrong material | Some plastics sustain flame readily | Know what it is before it goes in |
| Unattended machine | A flare has minutes to become a fire | Stay in the room |
| Very thin material | Paper and fabric flare with almost no warning | Lowest power that cuts; watch continuously |
The bed is a fire risk in itself
A honeycomb bed fills with sawdust and small offcuts. They are directly under the cut, dry, and getting hit by the beam every time it passes through the material. A bed that has not been cleaned in twenty jobs is a tray of kindling positioned under a heat source.
- Vacuum the honeycomb regularly — it takes a minute.
- Remove offcuts before starting a new job, not after.
- Check for a part that has dropped through and is sitting in the tray.
- A slat bed hides less but still collects dust underneath.
Within reach, before you need it
- CO2 extinguisher. Leaves no residue, so it will not destroy the machine’s optics and electronics the way powder does.
- Fire blanket. For smothering something small without discharging anything into the machine.
- A bucket of water is a reasonable last resort for a wood fire, and a bad idea near mains electronics. Cut power first.
- A working smoke alarm in the room — not in the hallway.
Why "unattended" keeps appearing
Laser jobs are long and boring, and the machine is usually doing exactly what it should. The temptation to leave it running is strong and entirely understandable. The problem is that the window between "small flare" and "workshop fire" is measured in tens of seconds, and nobody is present to notice which one is happening.
If a long job genuinely has to run, at minimum: stay in the same room, keep the extraction running, and do not start it as the last thing before leaving. Camera monitoring is better than nothing and is not the same as being there — a camera cannot open a lid or cut the power.
After a fire, however small
- Clean soot off the lens and mirrors before the next job. Soot absorbs the beam and causes the next problem.
- Check the air assist line has not melted.
- Check the extraction ducting — a fire can draw burning debris into it.
- Work out which of the causes above it was, before running the same job again.
Common questions
Is it normal to see flames while laser cutting?
A small flame at the cut that goes out as the head moves on is normal — the laser cuts by burning. What is not normal is a flame that persists after the head has passed, travels along the kerf, or appears in the debris tray. Any of those means stop the job.
Can I leave a laser cutter running unattended?
No. The gap between a routine flare and a serious fire is tens of seconds, and the whole point is that nobody is there to tell which is happening. Camera monitoring helps you notice but cannot open a lid, cut power or use an extinguisher.
What kind of extinguisher should I keep near a laser cutter?
CO2, because it leaves no residue and will not destroy the optics and electronics. Keep a fire blanket too for smothering something small. Dry powder works but coats everything inside the machine in corrosive residue — right if the alternative is losing the building, wrong as a first reach.
Should I open the lid if something catches fire?
No — that feeds it air. Cut power to the machine and keep the lid closed to starve the fire, with an extinguisher ready. Open it only when you are certain the fire is out, or when you need to discharge an extinguisher into it.