Chemicals, Dust, Tools and Safety
Etchants, fiberglass dust, UV, hot tools and waste: exposures, controls and disposal.
The hazards at a glance
| Method | Main hazards | Main controls |
|---|---|---|
| Breadboard, perfboard | Hot iron, flux fume, lead (see Soldering) | See Soldering Safety, Fumes and ESD |
| Toner transfer and etching | Corrosive etchant, staining, fumes, hot iron, waste | Gloves, glasses, apron, ventilation, tray with a lid; hazardous-waste disposal |
| Photoresist | Caustic developer, UV light, solvents | Gloves and glasses; UV-blocking cover and eye protection |
| CNC milling | Glass-fiber and epoxy dust, flying chips, noise, rotating tools, fire (rare) | Enclosure, vacuum at the tool, respirator, glasses, hearing protection |
| Drilling and cutting boards | Dust, splinters, sharp edges | Dust mask, glasses, clamp the board |
| Reflow (oven, hot plate) | Burns, flux fume, fire | A dedicated oven; extraction; never leave it unattended |
| Assembly | See Soldering | Ventilation, hygiene |
General workshop rules (risk assessment, first aid, fire, chemicals) are in Workshop Safety. This is general information, not professional safety advice: read the safety data sheet of every chemical you use.
Etchants and chemicals
| Chemical | Hazard | Handling |
|---|---|---|
| Ferric chloride (40 % solution) | Corrosive (pH below 1), stains skin and fabric, attacks metals; harmful if swallowed | Nitrile gloves, glasses, apron; plastic or glass trays only; never steel or aluminum |
| Sodium persulfate | Oxidizer; irritant; can cause allergic reactions and asthma if the dust is breathed | Gloves, glasses; avoid dust; keep dry and away from flammables |
| Hydrochloric acid + hydrogen peroxide | Strongly corrosive; releases chlorine and heat; fumes irritate the lungs; peroxide burns skin | Outdoors or in a fume hood; add the peroxide to the acid carefully; never seal the container |
| Sodium hydroxide developer (about 0.7 %) | Caustic: eye damage; skin irritation (pH about 13.2) | Gloves, glasses; rinse spills with plenty of water |
| Acetone | Highly flammable, irritant | Ventilate; no flames; small amounts |
| Isopropyl alcohol | Flammable, irritant | Ventilate; cap the bottle |
| Flux and paste | Irritant; lead in leaded paste | See Soldering; wash hands |
Worked example: why ventilation matters for acid etchant
- A fume cupboard with a 0.4 × 0.3 m opening and a face velocity of 0.5 m/s moves 0.06 m³/s = 216 m³/h: 7 times the volume of a 30 m³ room per hour.
- An open tray in the same room, with only natural ventilation (about 1 air change per hour), keeps the vapor in the room. Work outdoors or at a hood with the lid on the tray, and keep the etchant warm only as long as needed.
- Follow the label: hydrochloric-acid etchants release chlorine and hydrogen chloride, both of which have low exposure limits (about 1 and 5 ppm).
- Wear nitrile gloves, wrap-around chemical splash goggles and an apron; long sleeves and closed shoes.
- Use plastic tools (plastic tweezers, tray) and a bath of warm water for heating; never put the tray on a hot plate.
- Label every bottle, keep chemicals away from children and pets, and never use food containers.
- Add acid to water, not water to acid, and peroxide to the acid slowly, with the mixture in an open container.
- Keep a bottle of water near, and know where the eyewash is.
- Never mix chemicals that you do not know to be compatible (bleach and acid give chlorine).
Dust from milling, drilling and cutting
FR-4 is glass-fiber cloth in epoxy resin. Cutting it makes a fine dust of glass and resin that irritates the skin, eyes and lungs, and accumulates in the machine. The fine fraction goes deep into the lungs. There is no safe level of “dust that itches”: keep it out of the air.
Worked example: dust from one milled board
- Outline: perimeter 138 mm × 1 mm bit × 1.6 mm deep = 221 mm³ = 0.41 g (FR-4 density 1.85 g/cm³).
- Drilling: 60 holes of 0.8 mm: 48 mm³ = 0.09 g. Isolation: mostly copper: 0.08 g.
- Total about 0.57 g of dust per board. If it all stayed in a 30 m³ room: 19.1 mg/m³, against a typical exposure limit for nuisance dust of about 5 mg/m³ (respirable; the limit for glass fiber dust and epoxy is stricter).
- With a vacuum at the tool capturing 99 %, the room level is 0.19 mg/m³ (table below).
| Capture at the tool | Dust in the room air | Against 5 mg/m³ |
|---|---|---|
| 0.0 % | 19.09 mg/m³ | above |
| 90.0 % | 1.91 mg/m³ | below |
| 99.0 % | 0.19 mg/m³ | below |
| 99.9 % | 0.02 mg/m³ | below |
- Vacuum at the cut: a dust shoe around the bit and a HEPA-filter vacuum (a normal vacuum blows fine dust back out).
- Enclose the machine (a box with a window or a hood) and clean it with the vacuum, not a brush or compressed air.
- Wear a respirator (FFP2/N95 at least; P3 or P100 for regular use) and glasses; wash your hands and change clothes after.
- Wet cutting or a water mist keeps the dust down for hand cutting and sanding.
- Hearing protection for a spindle at 24 000 rpm and a vacuum (see Noise and Hearing Protection).
- Fire: never leave the machine unattended; a stuck bit or a dust cloud can ignite (see Fire, Fuels and Explosion).
Details of the machine and workholding are in CNC Isolation Milling and CNC Machining; ventilation and capture velocity in Dust, Fumes and Ventilation.
UV exposure units
Photoresist is exposed with UV-A (about 365 to 405 nm). UV can injure the eyes and skin, and cheap UV lamps are not always filtered or shielded. Never look into an exposure unit, and keep the lid closed during exposure.
Worked example: the exposure limit for UV-A
- A commonly used occupational limit for UV-A (ACGIH) is 1 J/cm² (1 000 mJ/cm²) over an 8-hour day for exposure to the eyes and skin.
- A bench exposure lamp giving 3 mW/cm² reaches the limit in 1 000 ÷ 3 = 333 s (about 5.6 min); a strong lamp at 10 mW/cm² in 100 s.
- A board exposure of 150 mJ/cm² is 15 % of that limit: fine for the exposure itself, but looking at a lit lamp, or leaving it on beside you, is not. Use a shielded box and UV-blocking glasses.
Hot tools and reflow
| Tool | Temperature | Hazard |
|---|---|---|
| Etchant at 40 °C | 40 °C | prolonged contact: irritation; it is the chemical that harms |
| Hot plate for reflow | 230 to 260 °C | instant burn on contact; stays hot for many minutes |
| Soldering iron | 300 to 400 °C | instant burn |
| Hot-air nozzle | 300 to 400 °C air | burn at 5 cm |
- Dedicate the oven (and the hot plate and tray) to electronics: flux and solder fume do not belong in a kitchen.
- Ventilate the reflow: flux fume (see Soldering Safety, Fumes and ESD).
- Never leave an oven or hot plate on and unattended; use a timer and a smoke detector.
- Let it cool before touching; mark hot plates and keep them out of the reach of children.
- Burn first aid: cool under running water for 20 minutes and seek help for anything large or deep.
Waste and disposal
Worked example: how much hazardous waste do you make?
- Each board of the example removes about 1.88 g of copper from a 100 × 100 mm blank with 60 % etched away (see Home Etching: Toner Transfer and Photoresist). A liter of etchant handles about 16 such boards at 30 g/L.
- 50 boards a year use about 3.1 liters of etchant, which ends up as waste containing about 94 g of copper dissolved as chloride.
- That is a small quantity, but it is not suitable for the drain: copper is toxic to aquatic life and the solution is acid. Collect it.
- Spent etchant: store in a labeled, sealed plastic container and take it to a hazardous-waste collection. Never put it down the drain, on the ground or in the bin. Some makerspaces and suppliers take it back; copper can be recovered.
- Developer and rinse water from photoresist: dilute alkali, but check the local rules; solvents (acetone, alcohol) as flammable waste.
- Dust, offcuts and failed boards: sweep up with a HEPA vacuum and bag them; the glass fiber and epoxy go with ordinary waste (not recycling) unless local rules differ; leaded boards and solder waste are hazardous (see Soldering).
- Used swarf and toner cartridges follow local rules.
- Spills: contain with sand or absorbent, wear gloves, collect and dispose as above; wipe the surface with plenty of water.
PPE, first aid and the safe bench
| Item | For | Standard |
|---|---|---|
| Safety glasses | Milling, drilling, cutting, soldering | ANSI Z87.1 or EN 166 |
| Chemical splash goggles | Etchant and developer | Indirect vent, ANSI Z87.1 D3 |
| Nitrile gloves | Chemicals; not near a rotating tool | EN 374 |
| Respirator | Dust (FFP2/N95 to P100); acid gas cartridge for HCl etchants | EN 149 / NIOSH |
| Hearing protection | Spindle and vacuum | EN 352 |
| Apron or old clothes | Etchant stains and eats fabric | — |
| UV-blocking glasses | Exposure units | UV-A blocking |
- Eye splash: flush with clean water for 15 minutes, holding the lids open; seek medical help.
- Skin contact: wash with plenty of water for at least 10 minutes; remove contaminated clothing.
- Swallowed: rinse the mouth, do not induce vomiting; call the poison center with the product name.
- Breathing fumes: go to fresh air; seek help if breathing is difficult.
- Keep the safety data sheets and the emergency numbers where you work.
- Do not eat, drink or smoke in the work area; wash hands afterwards.
- Electrical safety: use a residual-current device (RCD) on the bench supply; unplug before working inside equipment (see Electrical Safety).
Troubleshooting
| Symptom | Likely cause | What to do |
|---|---|---|
| Itchy skin or eyes after milling | Glass-fiber dust | Wash with cold water; improve the vacuum; wear gloves and glasses |
| Cough or sore throat after etching | Fumes from the etchant | Move to fresh air; use a hood or work outdoors; lid on the tray |
| Stained skin and clothes | Ferric chloride splash | Wash at once; wear an apron and gloves |
| Etchant has turned the tray or tools brown | Wrong materials | Use plastic or glass; replace metal tools |
| Smell of burning from the oven | Flux or board scorching | Switch off; ventilate; check the profile and the board |
| Etchant container swells | Gas from an acid-peroxide mix in a sealed container | Vent it outdoors; use a vented cap or an open container |
Related
- PCB Prototyping: the overview of this guide.
- Home Etching: Toner Transfer and Photoresist and CNC Isolation Milling: the methods these precautions apply to.
- Workshop Safety: the whole workshop.
- Soldering Safety, Fumes and ESD.
FAQ
Is ferric chloride dangerous?
It is corrosive and stains everything. It is not very volatile, so skin and eye protection matter most; handle it in plastic with nitrile gloves, glasses and an apron.
How do I dispose of used PCB etchant?
Collect it in a sealed plastic container and take it to a hazardous-waste facility. It holds dissolved copper and is acidic: never pour it down the drain.
Is fiberglass dust from milling harmful?
Yes: it irritates skin, eyes and lungs. Use vacuum extraction at the tool, an enclosure, a respirator and glasses.
Can I etch boards indoors?
Ferric chloride and persulfate can be used with ventilation and care; acid-peroxide etchants need a hood or the outdoors.
Is UV from a photoresist exposure unit dangerous?
It can harm the eyes and skin. Use a shielded box, keep the lid closed and wear UV-blocking glasses if you must look.
References
- Safety data sheets for ferric chloride, sodium persulfate, hydrochloric acid, hydrogen peroxide, sodium hydroxide, acetone and isopropyl alcohol.
- ACGIH, Threshold Limit Values and Biological Exposure Indices; OSHA 29 CFR 1910.1000 (air contaminants); UK HSE EH40/2005.
- ANSI Z87.1 (eye protection); EN 149 and NIOSH 42 CFR 84 (respirators).
Last reviewed: October 2026. Exposure limits change: use those that apply in your country. This is general information, not professional safety advice.