Lasers, 3D Printers, CNC and Soldering
The particular hazards of lasers, 3D printers and resin, CNC machines, soldering and batteries, with links to the full guides.
Laser cutters and engravers
A Class 4 laser can blind in a fraction of a second, start fires and give off toxic fume. The whole subject has its own page in the Laser Cutting guide: Laser Safety, Fire and Fumes. The essentials:
- Use an enclosed machine with an interlocked lid, a window that blocks the wavelength, and an emergency stop.
- Wear goggles rated for your laser’s wavelength (an 80 W CO₂ beam needs about optical density 4) whenever the beam path is open.
- Never leave it running; fire is the commonest accident. Keep air assist on and an extinguisher at hand.
- Never cut PVC, vinyl or anything with chlorine; the fume is toxic and corrodes the machine. Extract outdoors.
- Keep the beam inside: a stray beam of an 80 W CO₂ laser is hazardous for over 150 m.
3D printers
A desktop printer is a hot machine that melts plastic for hours, often unattended. The hazards are burns (hotend 200 to 300 °C, bed to 110 °C), fire from a heater that runs away, fume and particles from the hot plastic, and moving parts. The printing guide covers settings; this is the safety side (see 3D Printing and Additive Manufacturing).
Worked example: ultrafine particles
- Printing ABS can emit of the order of 1011 ultrafine particles per minute (typical order; PLA emits much less, 109 to 1010). In a 50 m³ room with 3 air changes an hour (Q = 2.5 m³/min) the steady concentration is 1011 ÷ 2.5 = 4.0 × 1010 per m³, or 40 000 per cm³: 4.0 times a typical city street (about 10 000 per cm³).
- With 10 air changes the level is 12 000 per cm³. An enclosure that holds 99 % of the emission inside brings the room level to about 400 per cm³, and a HEPA filter (99.97 %) on the exhaust cuts the air leaving it to 12 per cm³ in the same room.
- The hazard grows with the temperature: ABS (240 °C), ASA and nylon give off more and more irritating vapor (styrene, caprolactam) than PLA or PETG (230 °C).
Worked example: a runaway hotend
- A hotend heater block of 10 g aluminum has a heat capacity of 9 J/K. If the thermistor fails and the controller keeps the 40 W heater on, the temperature rises at up to 4.4 K/s (3.6 K/s with 8 W lost to the plastic and the air).
- From 220 °C it reaches 260 °C (where PTFE tube starts to give off toxic fumes that kill pet birds and cause “polymer fume fever” in people) in 9 s, 280 °C in 14 s and 500 °C in about 79 s: hot enough to ignite most things.
- Thermal-runaway protection in the firmware stops this by cutting the heater when the temperature does not rise as expected, and a second temperature cut-out or a thermal fuse is a hardware backstop. Make sure it is enabled and tested (many kit and modified printers had it turned off).
- The bed is similar: 240 W into a 0.5 kg plate is 0.5 K/s: it can pass 110 °C in a few minutes of a fault.
- Do not leave a printer running unattended or overnight unless it has runaway protection, a smoke alarm in the room and nothing flammable around it.
- Put it on a non-flammable surface and keep filament, paper and spray cans away.
- Print toxic plastics in an enclosure with extraction, not in the room you sleep in.
- Let the nozzle and bed cool before you touch them, and use tools to remove parts; wear glasses when cutting off supports (they spring).
- Check the wiring and connectors: a loose heater or bed connector overheats and melts (a common cause of printer fires).
- Use a smart plug or a fuse only if it is rated for the load, never to replace the controller’s protection.
Resin, powder and UV
- Liquid photopolymer resin is a skin sensitizer: contact can cause a lifelong allergy. Wear nitrile gloves (change them if they tear or get resin on the inside), safety glasses and long sleeves; never touch resin or a wet print with bare hands.
- Wash prints in isopropyl alcohol (a flammable solvent) in a closed container or a wash station; keep the alcohol away from ignition sources.
- Cure fully in a UV chamber; uncured resin on a print stays sensitizing. Never look at the UV lamp; use a closed or shielded lamp.
- Dispose of resin by curing it solid first: pour waste resin into a clear container and leave it in sunlight or a UV lamp, then bin the solid; never pour liquid resin down the drain.
- Powder printers (SLS and metal) make very fine, sometimes combustible or toxic powder: use a closed system, grounded tools and a HEPA vacuum, and follow the SDS.
- Ventilation: a resin printer in a bedroom is a bad idea; use a vented enclosure or a room with fresh air (see Dust, Fumes and Ventilation).
Worked example: why a tiny contact matters
Resin that sensitizes does so with a small repeated dose, not a large one. Touching a print with a glove contaminated by just 0.5 mL of resin a few times over 30 minutes a day is enough over months. The control is not “be careful” but a routine: gloves on, bin the gloves, wipe surfaces with IPA, wash hands, never carry resin gloves out of the room.
CNC machines, mills and routers
A CNC router or mill moves a spinning cutter under computer control, often fast, and will not stop if your hand is in the way. The CNC guide covers the process (see Troubleshooting, Accuracy and Safety); the essentials are:
Worked example: energy of a thrown piece
- A 12 mm cutter at 12 000 rpm has a tip speed of π × 0.012 × 12 000 ÷ 60 = 7.5 m/s (a 6 mm cutter at 24 000 rpm: 7.5 m/s).
- A broken piece of a cutter of 10 g leaving at the tip speed carries ½ × 0.010 × 7.5² = 0.28 J: enough to break skin or an eye.
- A workpiece torn from the clamps is the bigger danger: a 200 g offcut thrown at 10 m/s carries 10 J. A 6 mm polycarbonate window absorbs perhaps 48 J (illustrative), about 5 times that: use an enclosure with a polycarbonate window, not glass or acrylic, and never stand in the line of the cutter.
- The spindle takes seconds to stop after a stop command or a power cut (5 s here): keep hands out until it has stopped.
- Clamp the work properly and check the clamps are clear of the toolpath (see Workholding).
- Wear safety glasses and hearing protection, and tie back hair; no gloves near the spindle.
- Keep a hand on the emergency stop on the first run of any program, with the feed override low.
- Extract dust and chips at the cutter; a router makes a lot of fine dust (see Dust, Fumes and Ventilation).
- Use coolant carefully: mist is an irritant; watch for slippery floors and bacteria in old coolant.
- Do not machine magnesium or titanium chips dry: they burn; use special extinguisher (class D).
- Check the toolpath in simulation and with the spindle off before cutting.
Soldering and electronics
Worked example: lead on your hands
- A soldering iron at 350 °C is more than five times hotter than the 60 °C at which skin burns in a second: a touch of a fraction of a second burns. Keep the iron in its stand and never leave it on unattended.
- Leaded solder (63/37) is 37 % lead. A 0.8 mm wire has a mass of about 42 mg per cm and 16 mg of lead per cm: 0.47 g of lead in a 30 cm length of wire. Lead does not evaporate at soldering temperature (it melts at 327 °C, the solder at 183 °C) but it is carried on hands to the mouth, so wash hands before eating, never eat at the bench and keep solder off surfaces.
- The flux smoke (rosin) is a sensitizer and causes occupational asthma: use an extractor or a fan blowing the fume away from your face, with an opening for fresh air (see Dust, Fumes and Ventilation). Lead-free solder is not fume-free.
- Heat energy: a 60 W iron held for 20 s on a component delivers 1 200 J; keep the iron on a joint only as long as needed.
- Wear safety glasses: solder splashes and clipped leads fly.
- Use a stand and a damp sponge or brass wool; never flick solder; hold work in a clamp or third hand.
- Unplug mains equipment before opening it, and discharge capacitors (see Electrical Safety).
- Clean up and bin the lead-bearing waste properly: dross, wicks and sponge go to the hazardous-waste route.
- Static control (wrist strap, mat) protects components, not you; do not wear it near mains or high voltage.
- More on soldering is in the Electronics guide (Soldering).
Batteries and chargers
- A lithium-ion or LiPo pack holds a lot of energy: a typical 18 V 5 Ah tool pack holds 90 Wh (see Fire, Fuels and Explosion for the worked numbers).
- Use the charger that came with it, never charge a damaged, swollen, hot or wet pack, and never charge unattended on a combustible surface or overnight.
- Do not short the terminals; cover them, and keep loose packs out of boxes with metal.
- Store at room temperature, 30 to 60 % charge, in a metal or fire-resistant box.
- Lead-acid batteries give off hydrogen when charging: ventilate and keep sparks away; wear glasses (acid).
- Recycle used cells; tape the terminals before disposal.
Hot tools: heat guns, hot glue, irons
- Heat guns reach 500 to 650 °C: they strip paint (lead!) and ignite what is behind the work. Use a heat-resistant surface, never leave one on, and let them cool before storing.
- Hot-melt glue at about 150 to 200 °C sticks to skin and burns deeper than a spill: cool burns under running water at once.
- Hot-air rework stations and reflow ovens make fume and flux vapor: extract.
- Hot parts look like cold ones. Mark hot work, use tongs and wait.
Hazards by machine
| Machine | Main hazards | Key controls |
|---|---|---|
| Laser cutter | Eye damage, fire, toxic fume | Enclosure, interlock, goggles, extraction, never unattended |
| FDM 3D printer | Burns, fire (runaway), particles and fume | Runaway protection, enclosure, smoke alarm, extraction |
| Resin printer | Skin sensitization, vapor, UV, flammable IPA | Nitrile gloves, ventilation, cure fully, careful waste |
| CNC router or mill | Cutter, thrown parts, dust, noise | Enclosure, workholding, stop in reach, extraction, PPE |
| Soldering station | Burns, lead, fume | Stand, extraction, wash hands, safety glasses |
| Battery charging | Fire, short circuit | Right charger, not unattended, safe storage |
| Heat gun | Burns, fire, old paint | Heat-resistant surface, never unattended |
Troubleshooting
| Problem | Likely cause | Try |
|---|---|---|
| Printer smells strongly of plastic | High-temperature material, no extraction | Lower the temperature; enclosure with filter; ventilate |
| Printer smoke or smell of burning | Loose connector, overheating | Switch off and unplug; inspect the heater and bed connectors |
| Resin on the skin | Contact | Wash at once with soap and water (not alcohol); watch for a rash |
| Cutter breaks in the job | Too heavy a cut, poor clamping, wrong speed | Stop; wait for the spindle; check speed and feed; clamp |
| Burnt finger from the iron | Iron out of its stand | Cool running water for 20 minutes; always use the stand |
| Hot battery or swelling | Overcharge, damage | Stop using it; move it to a safe place outdoors; recycle |
Related
- Workshop Safety: the overview of this guide.
- Laser Safety, Fire and Fumes, 3D Printing and CNC Machining.
- Fire, Fuels and Explosion and Electrical Safety: fire, batteries and shock.
- Electronics Fundamentals: working on circuits.
FAQ
Is it safe to leave a 3D printer running overnight?
Only with thermal-runaway protection tested and enabled, a smoke alarm in the room and nothing flammable near it. Many fires have come from unattended printers with a failed heater or connector.
Do 3D printers give off harmful fumes?
They emit ultrafine particles and vapors, much more from ABS and ASA than from PLA; use an enclosure with a filter or ventilate, and keep the printer out of living and sleeping rooms.
Is resin dangerous to the skin?
Yes: it is a sensitizer and repeated contact can cause a lifelong allergy; wear nitrile gloves and treat uncured resin like a hazardous chemical.
Is lead solder safe to use?
The fume is mainly rosin flux, and lead does not evaporate at soldering temperatures, but lead on the hands is swallowed: wash before eating and never eat at the bench.
References
- Stephens, B., et al., Ultrafine particle emissions from desktop 3D printers, Atmospheric Environment 79 (2013); Azimi, P., et al., Emissions of ultrafine particles and VOCs from commercially available desktop 3D printers, Environmental Science and Technology 50 (2016).
- IEC 60825-1 (lasers); ANSI B11.8 and ISO 16090 (machining centers); IEC 62368-1 and IPC J-STD-001 (soldering).
- OSHA, Lead in construction and the SDS of your resins, solders and fluxes.
Last reviewed: October 2026. The emission rates, temperatures and energies are typical orders of magnitude: your machine and material will differ.