What type of solder is safest for home (hobbyist) use?

This advice is liable to be met with doubt and even derision by some - by all means do your own checks, but please at least think about what I write here:

I have cited a number of references below which give guidelines for soldering. These are as applicable for lead-free solders as for lead based solders. If you decide after reading the following not to trust lead based solders, despite my advice, then the guidelines will still prove useful.

It is widely know that the improper handling of metallic lead can cause health problems. However, it is widely understood currently and historically that use of tin-lead solder in normal actual soldering applications has essentially no negative health impact. Handling of the lead based solder, as opposed to the actual soldering, needs to be done sensibly but this is easily achieved with basic common sense procedures.

While some electrical workers do have mildly increased epidemiological incidences of some diseases, these appear to be related to electric field exposure - and even then the correlations are so small as to generally be statistically insignificant.

Lead metal has a very low vapor pressure and when exposed at room temperatures essentially none is inhaled. At soldering temperatures vapor levels are still essentially zero.

• Tin lead solder is essentially safe if used anything like sensibly.

  While some people express doubts about its use in any manner, these are not generally well founded in formal medical evidence or experience. While it IS possible to poison yourself with tin-lead solder, taking even very modest and sensible precautions renders the practice safe for the user and for others in their household.

• While you would not want to allow children to suck it, anything like reasonable precautions are going to result in its use not being an issue.

A significant proportion of lead which is "ingested" (taken orally or eaten) will be absorbed by the body.

BUT you will acquire essentially no ingested lead from soldering if you don't eat it, don't suck solder and wash your hands after soldering. Smoking while soldering is liable to be even unwiser than usual.

• It is widely accepted that inhaled lead from soldering is not at a dangerous level.

The majority of inhaled lead is absorbed by the body.

BUT the vapor pressure of lead at soldering temperatures is so low that there is essentially no lead vapor in the air while soldering. Sticking a soldering iron up your nose (hot or cold) is liable to damage your health but not due to the effects of lead. The vapor pressure of lead at 330 C (VERY hot for solder) / 600 Kelvin is about 10^-8 mm of mercury.

The major problems with lead are caused either by its release into the environment where it can be converted to more soluble forms and introduced into the food chain, or by its use in forms which are already soluble or which are liable to be ingested. So, lead paint on toys or nursery furniture, lead paint on houses which gets turned into sanding dust or paint flakes, lead as an additive in petrol which gets disseminated in gaseous and soluble forms or lead which ends up in land fills are all forms which cause real problems and which have led to bans on lead in many situations. Lead in solder is bad for the environment because of where it is liable to end up when it is disposed of. This general prohibition has lead to a large degree of misunderstanding about its use "at the front end".

If you insist on regularly vaporising lead in close proximity to your person by eg firing a handgun frequently, then you should take precautions re vapor inhalation. Otherwise, common sense is very likely to be good enough.

Washing your hands after soldering is a wise precaution but more likely to be useful for removal of trace solid lead particles.

Use of a fume extractor & filter is wise - but I'd be far more worried about the resin or flux smoke than of lead vapor.

Sean Breheney notes: " There IS a significant danger associated with inhaling the fumes of certain fluxes (including rosin) and therefore fume extraction or excellent ventilation is, in my opinion, essential for anyone doing soldering more often than, say, 1 hour per week. I generally have trained myself to inhale when the fumes are not being generated and exhale slowly while actually soldering - but that is only adequate for very small jobs and I try to remember to use a fume extractor for larger ones. (Added July 2021)

Note that there are MANY on we b documents which state that lead solder is hazardous. Few or none try to explain why this is said to be the case.

Soldering precautions sheet. They note:

• Potential exposure routes from soldering include ingestion of lead due to surface contamination. The digestive system is the primary means by which lead can be absorbed into the human body. Skin contact with lead is, in and of itself, harmless, but getting lead dust on your hands can result in it being ingested if you don’t wash your hands before eating, smoking, etc. An often overlooked danger is the habit of chewing fingernails. The spaces under the fingernails are great collectors of dirt and dust. Almost everything that is handled or touched may be found under the finger nails. Ingesting even a small amount of lead is dangerous because it is a cumulative poison which is not excreted by normal bodily function

Lead soldering safety guidelines

Standard advice Their comments on lead fumes are rubbish.

FWIW - the vapor pressure of lead is given by

Quoted from The Vapor Pressures of Metals; a New Experimental Method

Wikipedia - Vapor pressure

For more on soldering in general see Better soldering

Lead spatter and inhalation & ingestion

It's been suggested that the statement:

• "The majority of inhaled lead is absorbed by the body. BUT the vapor pressure of lead at soldering temperatures is so low that there is essentially no lead vapor in the air while soldering."

is not relevant, as it's suggested that

• Vapor pressure isn't important if the lead is being atomized into droplets that you can then inhale. Look around the soldering iron and there's lead dust everywhere.

In response:

"Inhalation" there referred to lead rendered gaseous - usually by chemical combination. eg the use of Tetraethyl lead in petrol resulted in gaseous lead compounds not direcly from the TEL itself but from Wikipedia Tetraethyllead page:

• The Pb and PbO would quickly over-accumulate and destroy an engine. For this reason, the lead scavengers 1,2-dibromoethane and 1,2-dichloroethane are used in conjunction with TEL—these agents form volatile lead(II) bromide and lead(II) chloride, respectively, which are flushed from the engine and into the air.

In engines this process occurs at far higher temperatures than exist in soldering and there is no intentional process which produces volatile lead compounds. (The exceedingly unfortunate may discover a flux which contains substances like the above lead scavenging halides, but by the very nature of flux this seems vanishingly unlikely in the real world.).

Lead in metallic droplets t soldering temperatures does not come close to being melted or vaporised at anything like significant partial pressures (see comments and references above) and if any enters the body it counts as 'ingested', not inhaled.

Basic precautions against ingestion are widely recommended, as mentioned above.

For lead "spatter" to qualify for direct ingestion it would need to ballistically enter the mouth or nose while soldering. It's conceivable that some may do this but if any does the quantity is very small. It's generally recognised both historically and currently that the actual soldering process is not what's hazardous.

A significant number of webpages do state that lead from solder is vaporized by soldering and that dangerous quantities of lead can be inhaled. On EVERY such page I have looked at there are no references to anything like reputable sources and in almost every such case there are no references at all. The general ROHS prohibitions and the undoubted dangers that lead poses in appropriate circumstances has lead to a cachet of urban legend and spurious comments without any traceable foundations.

And again ...

It was suggested that:

• Anyone who's sneezed in a dusty room knows that it doesn't have to enter the nose or mouth "ballistically". Any time solder splatters or flux pops, it creates tiny droplets of lead that solidify to dust. Small enough particles of dust can be airborne and small exposures over years accumulate in the body. "Lead dust can form when lead-based paint is dry scraped, dry sanded, or heated. Lead chips and dust can get on surfaces and objects that people touch. Settled lead dust can re-enter the air when people vacuum, sweep or walk through it."

In response:

A quality reference, or a few, that indicated that air borne dust can be produced in significant quantity by soldering would go a long way to establishing the assertions. Finding negative evidence is, as ever, harder.

There is no question about the dangers from lead based paints, whether form airborne dust from sanding, children sucking lead painted objects or surface dust produced - all these are extremely well documented.

Lead in a metallic alloy for soldering is an entirely different animal.

I am unaware of discernible "Lead dust" occurring from 'popping flux', and I'm unaware of any mechanism that would allow mechanically small lead droplets to achieve a low enough density to float in air in the normal sense. Brownian motion could loft metallic lead particles of a small enough size. I've not seen any evidence (or found any references, that suggest that small enough particles are formed in measurable quantities.

Interestingly - this answer had 2 downvotes - now it has one. Somebody changed their mind. Thanks. Somebody didn't. Maybe they'd like to tell me why? The aim is to be balanced and objective and as factual as possible. If it falls short please advise.

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Added 2020: SUCKING SOLDER?

I remember biting solder when I was a kid and for about 2 years I wouldn't wash my hands after soldering. Will the effects show up in the future??

I can only give you a layman's opinion. I'm not qualified to give medical advice.

You can be tested for lead in the blood very easily (it requires one drop of blood) and it's probably worth doing.

Internet diagnosis is, as I'm sure you know, a very poor substitute for proper medical advice. That said

Should I be worried?

Not really. In any case, the deed is done, so worrying won't retroactively fix anything. There's no "therapy" that would undo the exposure, since the exposure itself is so minuscule that it'd be hard to even quantitatively determine it just by taking samples from your body.

But, first of all: presence of lead in the solder is beside the point as far as fumes go in point soldering. Lead is important only in direct contact, i.e. you should wash your hands periodically while and after handling leaded solder. Don't lick tin-lead plated wire or component leads mindlessly, and don't lick your fingers while soldering. That's all there's lead-wise.

The fumes you're breathing during point-to-point/component lead soldering contain only trace amounts of the solder alloy. There would be way more of them - enough to be a concern - if you were hovering above a continuously-on solder pot, or worse yet - with an air leak from a wave soldering bath - but you're not doing that.

In hand-soldering, most of the fumes come from the flux. The flux fumes are comparable to various smoking/vaping products, except in much lower concentration, and should not be a problem in occasional use. If you want to keep the hobby, get a little fan to blow the fumes away, and work in a ventilated area.

If the area you're in is not ventilated well, use a whole-room air cleaner in addition to the fan. It will catch particulates from the flux, and adsorb the vapors. Make sure the air cleaner has both HEPA and carbon adsorber elements.

Solder "fume extractors" are a bit of a pointless thing if they don't provide serious air filtration or are not vented to outside. Any "extractor" that you can buy for a couple hundred bucks is not worth the the paper that comes with it as a "manual".

For occupational manual soldering on a production floor, the fumes are vented to outside, just as is the case in a welding booth, etc.

An aside: humans can actually get rid of small amounts of excess lead. The minuscule lead absorption in hobbyist leaded-solder circuit soldering is a couple orders of magnitude below our ability to shed lead. But now a kicker: The only way you can get rid of excess iron is by bleeding... No joke.

The solder does not change- the vapor pressure of lead increases with temperature but the amounts involved should still be pretty small for casual soldering.

Handling solder wire or PCBs with solder on is not so bad, though you should not do it when you're eating (especially acidic things like oranges- messes up the boards too). Washing your hands after handling solder or soldering is a reasonable precaution.

If you have a really crummy soldering iron or gun that gets excessively hot, not only will it damage PCBs but you will get excessive lead fumes. This might be an issue for 3rd world scavenging of parts using a propane torch or whatever (then you're getting nasty fumes from the epoxy and other stuff too).

The real danger is solder paste (used in SMT assembly) that you could accidentally spread on a Carr's water cracker in place of liver pâté. More seriously, it can get on your hands (under fingernails too) or clothes and be transferred to your mouth etc. since it is basically tiny balls of solder in a sticky gooey liquid.

Of course these dangers are greatly increased if you are with a child (they put all kinds of things in their mouths), and especially, if you are 'with child' (aka pregnant). Pb-free solder should be safer, but I would suggest still taking reasonable precautions.

As carveone says, breathing flux fumes is nasty- even good old rosin (eg. Kester 44) seems to stimulate asthma (it does in me), and the lead-free stuff needs more aggressive flux. I've got some rolls of solder from China, and have no idea what the flux contains. It's quite safe when it's cold, but aggressive chemically (by design) when hot.

Here's a fairly thorough look at the hazards of (wire) soldering done by a University (many of us have done things like this for companies, but they're not generally publicly available). It includes such useful suggestions as not touching the hot end of a soldering iron.

I can verify that soldering does produce beads and dusts in the area, even when you're careful. It's quite a bit more than some people make it out to be. If you keep your workstation clean and it is the proper colour, the solder has no grime or camouflage to hide amongst. An iron will mostly produce larger bits like beads and flakes, but solder vacuums are notorious for producing fine dusts.

If you're jumping back and forth between soldering and using the mouse/keyboard, then you should not be jumping back and forth between eating and using the mouse/keyboard.