LaserCanvas
Laser safety: eyes, fire and fumes
Three risks, in the order they catch people out. Fire — never run a job unattended, and keep a CO2 extinguisher or fire blanket within reach. Eyes — your glasses must state both a wavelength range that includes your laser and an OD rating, or they are decoration. Fumes — duct outdoors if you possibly can; a filter is a consumable, not a solution. Almost every hobby laser is Class 4, which is the most dangerous class there is.
Your machine is almost certainly Class 4
Laser classes run 1 to 4. Class 4 begins at 500 mW, which nearly every cutting laser exceeds by a wide margin — a 10 W diode is twenty times that threshold, and a 60 W CO2 is more than a hundred times.
Class 4 means three specific things: it can cause permanent eye injury, it can burn skin, and it is a fire hazard by definition. It also means the danger is not limited to looking directly into the beam — a diffuse reflection off a scattered surface is enough to injure an eye.
Eye protection: two numbers, both required
Laser eyewear is wavelength-specific. Glasses that protect you from a blue diode do nothing against a CO2 beam, and the reverse. Any pair worth wearing is marked with both of the following, printed on the frame:
- A wavelength range that includes your laser. Diode machines are around 445–450 nm; CO2 is 10,600 nm; fibre is around 1,064 nm.
- An optical density (OD) figure for that range. OD is logarithmic: OD 3 passes one thousandth of the light, OD 5 one hundred-thousandth. For Class 4 work, OD 5 or higher across your wavelength is the usual recommendation.
| Machine | Wavelength to look for | What to be careful of |
|---|---|---|
| Blue diode | 445–450 nm, OD 5+ | Orange-tinted glasses are common and many are unrated. A tint is not a rating. |
| CO2 | 10,600 nm, OD 5+ | Ordinary polycarbonate blocks 10,600 nm reasonably, which makes unrated eyewear feel convincing. Rated is still rated. |
| Fibre | 1,064 nm, OD 5+ | Near infrared is invisible — there is no blink reflex and no visible warning. |
The enclosure lid counts too. The orange acrylic panel on many diode enclosures is a wavelength filter doing real work — which is why running the machine with the lid open, or with a panel replaced by clear acrylic, quietly removes your main protection.
Fire is the risk that actually materialises
Eye injuries make the warnings; fires make the incidents. A laser is a device that deliberately heats material past its ignition point, a few millimetres from a pile of its own flammable dust. Small flare-ups are routine. The question is only whether one is left alone long enough to become a fire.
- Never run a job unattended. Not "stay in the building" — stay where you can see it. This is the whole rule; everything else is mitigation.
- Keep a CO2 extinguisher or a fire blanket within arm’s reach. Dry powder works but will destroy the machine; water is wrong near mains electronics.
- Clean the bed. Accumulated offcuts and resin dust under a honeycomb are excellent kindling and are the usual reason a flare-up becomes a fire.
- Air assist does more than improve edge quality — it actively starves small flames.
- Watch for the sustained flame. A brief flare as the beam crosses is normal; a flame that travels along behind the head is not, and means stop.
- Be especially careful with thin card, paper, felt and foam. They ignite easily and do not self-extinguish.
Fumes: the risk you notice last
Everything you cut is vaporised and ends up in the air. Wood smoke is an irritant and a long-term respiratory risk. MDF adds binder products. And some materials release things that are acutely dangerous — chlorine gas from PVC being the clearest case, which is why the forbidden list exists.
- Ducted outdoors beats filtered, for nearly every hobby setup. An inline fan pushing air out of a window is simple, effective and cheap.
- A filter box is a consumable. Activated carbon saturates. Once it has, the box is a noisy pipe that gives you confidence you have not earned.
- Negative pressure matters. If air leaks out of the enclosure rather than in, smoke is entering the room regardless of what the fan is rated at.
- Run extraction for a few minutes after the job as well. The plume does not stop when the beam does.
- A smell you have stopped noticing is not a smell that has gone away.
The things people skip
| Skipped | What it costs |
|---|---|
| Interlocks disabled "temporarily" | The one protection that works when you are distracted. Temporary lasts years. |
| Running with the lid open for a quick job | Scattered Class 4 light in the room, and smoke straight into your lungs |
| Cutting unlabelled plastic | Possibly chlorine gas, and corrosion that appears months later |
| No extinguisher in the room | A recoverable flare-up becomes a call to the fire service |
| Children or pets with access | An open-frame machine at desk height is at eye height for both |
A five-minute setup that removes most of the risk
- Buy eyewear rated for your wavelength at OD 5+, and check the frame markings when it arrives.
- Put a CO2 extinguisher or fire blanket within reach of where you stand.
- Duct the extraction outdoors, and confirm the enclosure pulls air in at the seams.
- Clear the bed of debris and check the honeycomb is not clogged.
- Agree with yourself that no job runs while you are out of the room. That one is free and does more than the rest combined.
Common questions
Do I need laser glasses if my machine is enclosed?
The enclosure is the primary protection while it is closed and its interlock works. Glasses matter for the moments the enclosure does not cover: alignment, testing, focusing and anything done with the lid open. Many people keep a rated pair beside the machine specifically for those.
What OD rating do I need?
OD 5 or higher across your laser’s wavelength is the usual recommendation for Class 4 work. The rating only counts for the wavelength range printed beside it — OD 6 at 450 nm offers you nothing against a CO2 at 10,600 nm.
Are the glasses that came with my laser any good?
Check the frame. If it states a wavelength range and an OD figure, it is making a claim you can evaluate. If it states neither, treat it as tinted plastic and buy a rated pair — this is a common enough problem that assuming the worst is reasonable.
Is an air purifier enough instead of ducting outside?
A room air purifier is not designed for this and will not keep up with a cutting plume. A purpose-built laser fume extractor with fresh carbon can work where ducting is impossible, but the carbon saturates and must be replaced on schedule rather than when it smells. Ducting outdoors is simpler, cheaper and more reliable.
What kind of fire extinguisher should I keep near a laser cutter?
CO2 is the usual recommendation near electronics, because it leaves no residue. A fire blanket handles small contained flare-ups well. Dry powder works but contaminates the machine thoroughly, and water is a poor choice around mains-powered equipment.