Fire and ventilation

A laser focused on a flammable material is a torch. The only thing keeping a job from turning into a fire is the air assist and the moving head. When something goes wrong, those stop helping immediately.

About this page

Laser engravers and cutters use intense light, often at wavelengths your eye cannot see. Improper use can cause permanent eye injury, severe burns, fire, and property damage.

I am a maker, not a fire-safety or industrial-hygiene professional. The guidance below reflects practical experience and published reference material; it is not a substitute for:

• The safety documentation, warnings, and labels that shipped with your machine and any extraction or suppression equipment.
• The safety data sheet (SDS) for any material you intend to cut, engrave, or burn.
• Local fire, building, electrical, and ventilation codes.
• Advice from a licensed installer if you are routing exhaust through a wall or roof.

When this page and the manufacturer disagree, the manufacturer wins. Beam Bench (the app and these docs) is provided as-is with no warranty; running a laser is your responsibility. See the terms for the full disclaimer.

Never leave a running job unattended

This is the rule. Almost every laser fire in the maker community involves someone who stepped away for "just a minute". The job ran into a knot in plywood, or hit a pocket of pitch, or the air assist failed silently. By the time they came back, the machine was a torch.

Stay with the machine. Watch the head. If you smell something acrid that wasn't there a moment ago, stop the job and lift the lid.

Have an extinguisher within arm's reach

Recommended: Class ABC dry chemical or CO2. Both work on the kinds of fires lasers start (paper, wood, plastic, electrical).

Not recommended: water. Water near a powered machine is an electrical hazard. Water can also splash burning material around.

Mount the extinguisher on the wall next to the laser, not across the room. In a fire, you have seconds.

Ventilation

Almost every material you cut or engrave produces smoke. The smoke from many common materials is toxic in concentrations easily reached in a closed room.

• Acrylic: chlorinated grades are deadly (do not cut, see Materials). Cast acrylic produces irritating but manageable smoke.
• MDF and plywood: the glue is the problem. Phenolic and urea-formaldehyde resins release formaldehyde and other carcinogens when burned.
• Leather: chrome-tanned leather releases hexavalent chromium when lasered. Vegetable-tanned is far less bad.
• Coated metal anodizing / engraving: generally OK with extraction.
• Foam, rubber, anything with chlorine: see Materials. Do not cut.

Build the extraction

1. Inlet at the laser, capturing fumes at the cut point. Most enclosed lasers have one built in. Open-bed lasers need a hood positioned over the work.
2. Duct carries fumes from inlet to outlet. Use rigid duct or wire-reinforced flex. Smooth-bore is more efficient than ribbed.
3. Fan with enough static pressure to overcome the duct length and any filtration. Inline duct fans rated for the airflow your laser manufacturer specifies. For small diode lasers, 4-inch / 100 mm at 200+ CFM is typical. For CO2 lasers, 6-inch / 150 mm at 400+ CFM.
4. Outlet to outside. Not into your shop. Not into your attic. Outside.

In-line carbon filters do not replace venting outside. They reduce odor for re-circulated systems but do not remove fine particulates well, and they saturate. If you must use a filter (e.g. apartment dweller, winter in a cold climate), buy from a laser-specific brand, replace cartridges on schedule, and crack a window.

Air assist

Air assist (a stream of air at the cut point) reduces flare-up, blows smoke away from the lens, and improves cut quality.

• Always use air assist for cutting.
• For engraving on flammable materials, even a low-pressure assist reduces flare risk substantially.
• Check that the air assist is on before you start the job. Forgetting is a common cause of fires.

What to do

• Stay with running jobs.
• Mount an ABC dry chemical or CO2 extinguisher within arm's reach.
• Vent fumes to outdoors with adequate fan and ducting.
• Use air assist for every cut.
• Test that the interlock (lid switch) actually stops the laser by opening the lid mid-job once a month.
• Clean the bed and tray weekly. Built-up debris is fuel.

What not to do

• Do not leave the room while a job is running.
• Do not vent into an enclosed shop or attic.
• Do not rely on a recirculating carbon filter as your only ventilation in a closed room.
• Do not cut materials you have not verified are safe (see Materials).
• Do not use water on a laser fire while the machine is powered.