Soldering Safety, Fumes and ESD

The hazards at a glance

Hazard	Harm	Main control
Hot iron (350 °C and over)	Burns, fire	Stand, no clutter, never leave it on; cool burns under running water for 20 minutes
Flux fume	Occupational asthma, irritation	Local extraction at the work; ventilation
Lead in solder	Poisoning by swallowing, long-term nervous and blood effects	Wash hands, no eating or drinking at the bench, clean surfaces
Splashes and clipped leads	Eye injury	Safety glasses
Static electricity	Damaged components, latent failures	ESD mat, wrist strap, humidity, handling
Solvents (isopropyl alcohol)	Fire, irritation	Keep small amounts away from the iron; ventilate
Mains-powered equipment	Electric shock	Unplug first; discharge capacitors; use an RCD (see Electrical Safety)
Repetitive strain and poor posture	Neck, eye and wrist strain	Good lighting, a comfortable bench, breaks

Soldering is a low-risk activity when the basic precautions are in place. For the workshop as a whole (fire, first aid, chemicals) see Workshop Safety, in particular Lasers, 3D Printers, CNC and Soldering.

Flux fume and extraction

The “smoke” from soldering is mostly flux vapor and its decomposition products, not solder. Rosin (colophony) fume is a recognized respiratory sensitizer: repeated exposure can lead to occupational asthma, which can be permanent, and to irritation of the eyes and throat. It is a fume of fine particles, so a face mask for dust does not remove the vapor, and diluting it in the room is not enough.

The flow needed to capture the fume at the source depends on the distance to the hood. For a plain opening, the Dalla Valle formula gives the flow for a capture velocity v at distance x from a hood of area A:

Q = v × (10 x² + A)

Distance to the joint	Flow for a 10 × 10 cm hood	In m³/h
5 cm	8.75 L/s	32 m³/h
10 cm	27.50 L/s	99 m³/h
15 cm	58.75 L/s	212 m³/h
20 cm	102.50 L/s	369 m³/h
30 cm	227.50 L/s	819 m³/h

Capture efficiency	Fume reaching the room	Room concentration	Against 0.05 mg/m³
0 %	2.00 mg/min	4.00 mg/m³	above the limit
50 %	1.00 mg/min	2.00 mg/m³	above the limit
90 %	0.20 mg/min	0.40 mg/m³	above the limit
99 %	0.02 mg/min	0.04 mg/m³	within the limit

• Use a filter extractor: a carbon filter takes out odors and organic vapors, a HEPA stage the particles. Replace the filters on schedule.
• Exhaust to the outside where possible; recirculating units are fine only with the proper filters.
• Position the plume: fume rises, so a fan that blows across the work pushes it into your face. Pull it away from you.
• Lead-free fluxes are harsher, so extraction matters more.
• Keep the numbers as a guide: measured exposure depends on the flux, the temperature and the airflow.

Lead and hygiene

Leaded solder is 37 to 40 % lead. At soldering temperature (350 °C) lead produces almost no vapor, so the airborne hazard is small. The risk is ingestion: lead on the hands is carried to the mouth with food, drink, tobacco or nail-biting. Lead accumulates in the body and harms the nervous system, blood and kidneys, and is especially dangerous to children and to pregnancy.

• Wash your hands with soap and water after soldering and before eating, drinking or smoking; do not eat or drink at the bench.
• Clean the bench with a damp wipe, not a dry brush or a vacuum without a HEPA filter, and dispose of solder waste (dross, wick, offcuts) as hazardous waste per local rules.
• Keep it from children and pregnancy: pregnant workers and children should not handle leaded solder.
• Lead-free is not hazard-free: the flux fumes are the same or worse, and the high temperature adds burn risk. Tin, silver and copper alloys are far less toxic than lead, though.
• Cadmium in some brazing alloys, and the bismuth, antimony, zinc and fluoride in other solders and fluxes, need their own data sheets.

Burns and fire

The iron’s tip is at 300 to 400 °C. Contact burns are instant, and a hot iron left on a bench can start a fire. The skin burns not only by touching the iron but also by splashes of molten solder (about 200 to 250 °C when it lands), hot-air streams and hot parts that look cool.

Surface temperature	Time to a serious burn (approx.)
44 °C	about 6 hours
48 °C	about 10 minutes (adult)
55 °C	about 30 seconds
60 °C	about 5 seconds
70 °C	under 1 second

The times are typical for adult skin; children’s skin burns faster. They show how a surface at 60 °C burns in seconds, and an iron at 350 °C in a fraction of one.

• Always use the stand, a heavy one that does not tip, with the iron cord clear of the hot tip.
• Treat the iron as hot until it is off and cooled for several minutes, and do not hand tools to others by the tip.
• Clear flammables from the bench: paper, solvents, plastics, packaging foam.
• Burn first aid: cool the burn under cool running water for 20 minutes, remove rings and watches before swelling, cover loosely with cling film or a clean dressing and get help for large or deep burns or burns on the face and hands. Do not use ice, butter or creams.
• Have a fire plan: know where the extinguisher is (a CO₂ or dry powder type for electrical fires) and how to switch off power (see Fire, Fuels and Explosion).

Eyes and flying parts

Wear safety glasses with side shields (to ANSI Z87.1 or EN 166). Solder spits when it meets water or wet flux, hot flux can spatter, and clipped component leads fly off at high speed. Wire clipping is the most common cause of eye injuries at the bench.

Static discharge (ESD)

Electrostatic discharge is a safety topic for the parts, not for you. A person walking across a room can build up thousands of volts without noticing, because the human body only feels a discharge above about 3 000 V. Many semiconductor devices are damaged at far less than that, sometimes visibly (a dead part) but often invisibly: a latent defect that shows up weeks later.

Action	Voltage at 10 to 20 % RH	Voltage at 65 to 90 % RH
Walking on carpet	35 000 V	1 500 V
Walking on vinyl	12 000 V	250 V
Working at a bench	6 000 V	100 V
Plastic bag picked up	20 000 V	1 200 V
Plastic foam packaging	26 000 V	500 V

ESD sensitivity class (human body model)	Withstands up to
Class 0	under 250 V
Class 1A	250 to 500 V
Class 1B	500 to 1 000 V
Class 1C	1 000 to 2 000 V
Class 2	2 000 to 4 000 V
Class 3A	4 000 to 8 000 V

E = ½ C V², I_peak = V ÷ R

• Set up an ESD-safe work area with a dissipative mat grounded through 1 MΩ and a wrist strap to the same ground point; keep plastics, foam and clothing that charge away from the work.
• Handle parts by their bodies, not the leads; keep them in conductive bags or tubes until needed; touch the mat or the bag before the part.
• Use a grounded soldering iron (the tip should have a resistance of under 2 Ω to ground per ESD standard ANSI/ESD S20.20).
• Do not wear a wrist strap near a live mains circuit without a resistor and an RCD; the strap protects the part, not you.
• Keep the humidity 40 to 60 % where you can.

Chemicals: flux, solvents and cleaners

• Read the safety data sheet (SDS) of each flux, paste and cleaner.
• Isopropyl alcohol is flammable and a mild irritant: small amounts, a closed container, no hot iron nearby, good ventilation.
• Acid fluxes and some water-soluble fluxes irritate skin and eyes and corrode tools: gloves and glasses.
• Solder paste contains lead (if leaded) and flux: wear nitrile gloves, wash up afterwards and do not put the paste near food. Keep it refrigerated and in a labeled container.
• Flux residue on the hands: wash before touching the face. Do not use solvents to clean skin.
• Dispose of used wick, dross, paste and solvent rags as chemical waste (lead is hazardous waste); do not put used solvent rags in a bin with other rubbish.

The safe bench

• Iron in a heavy stand; mat that withstands heat; no clutter and no flammables.
• Extractor within 15 cm of the work; room ventilated.
• Safety glasses on; hair tied back; sleeves short or tight; no loose jewelry.
• Good light (over 1 000 lux) and magnification.
• ESD mat and strap if handling sensitive parts.
• Soap and a wash basin, a first-aid kit with burn dressings and a cold-water supply within reach.
• Equipment unplugged before working inside it; capacitors discharged.
• Iron off when you leave, even for a minute.

Troubleshooting

Symptom	Likely cause	What to do
Coughing, sore eyes or wheezing when soldering	Flux fume sensitization	Improve extraction; stop and see a doctor if it continues
Smell of burning plastic or board	Iron too hot or in contact	Stop; check the tip temperature; unplug equipment
Chip fails some time after assembly	Latent ESD damage	Improve ESD control; handle parts in bags
Static shocks at the bench	Low humidity, wrong clothing or mat	Humidifier, grounded mat and strap
Metallic taste or tingling hands	Lead exposure from poor hygiene	Wash, stop eating at the bench; see a doctor if concerned
Burn	Contact with iron or solder	Cool under running water for 20 minutes; seek help for large burns

Related

• Soldering: the overview of this guide.
• Solder Alloys, Flux and Paste: flux types and cleaning.
• Irons, Stations, Tips and Hot Air: the bench set-up.
• Workshop Safety: the whole workshop.

FAQ

Is soldering fume dangerous?

The flux fume can cause occupational asthma and irritation after repeated exposure, so use extraction at the work. The lead hazard is mainly from hand-to-mouth contact.

Do I need a fume extractor?

For regular soldering, yes. A small filter unit within 15 cm of the work works far better than ventilating the room.

Can lead poisoning come from soldering?

Rarely from fumes, but it can happen through the hands to the mouth. Wash after soldering and never eat or drink at the bench.

Is a wrist strap dangerous?

Not when it has the standard 1 MΩ resistor. Do not use one near live mains conductors without proper protection.

How do I treat a soldering burn?

Cool it under cool running water for 20 minutes, cover it loosely and seek medical help for anything large, deep or on the face, hands or joints.

References

• UK HSE EH40/2005, Workplace Exposure Limits (rosin-based solder flux fume); HSE leaflet on soldering fume (INDG248).
• ANSI/ESD S20.20, Protection of Electrical and Electronic Parts, Assemblies and Equipment; JEDEC JS-001 (human body model).
• OSHA 29 CFR 1910.1025 (lead); ANSI Z87.1 (eye protection); IPC J-STD-001 (safety notes).

Last reviewed: October 2026. Exposure limits and ESD levels change: check the current standards and your country’s regulations. This is general information, not legal or professional safety advice.