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Flux toxicity

Years ago, when I first learnt to solder, I used a borax cone in a
dish with water to make flux.

I still do, because it’s how I was taught and it works well.
However, what i was never taught about was any H&S issues.

data sheets are confusing me; many seem to suggest that borax flux
is not a problem, some suggest you shouldn’t touch it, some say that
chronic exposure to the fumes causes coughing.

I’d be very grateful for any enlightenment!

thank you,

The MSDS for Borax gives a TLV of 10 mg/m3. This indicates that borax
is considered a “nuisance” dust. If the level is high enough it could
cause mechanical problems such as plugging up the nasal passages, but
no toxic effects would be expected. However, one would need to work
very hard to get this kind of dust concentration, it would be a near
permanent, visible dust cloud in the air. This is not likely from
most silver soldering unless one is doing a mammoth production
soldering process and you would llikely need automated dust
generating equipment. It is also good to remember that the TLV
(threshold limit value) is a level that workers could be exposed to
8-10 hours per day, 5 days per week for 30-40 years with no adverse
health effects. So for hand soldering with borax flux, I would not
expect a problem as you will probably not produce a measurable level
of borax fume or dust in your breathing zone.

HOWEVER!!! Some fluxes may contain cadmium and that is a horse of a
different road clearance. Cadmium is a suspected human cancer
causing material as well as having some unpleasant skin effects. If
you are using a flux with cadmium, special precautions should be
taken or even better, use another type of flux.

Hope this helps
Jim J

Thank you Jim, very much. That helps a great deal. I’m pretty sure
there’s no cadmium involved (I use tha simple cone and dish yfrom (hidden in the other fluxes!) and it comes with no
info at all except “borax cone”. I think if it had cadmium in it
would have to be listed.

Thanks for making sense of the msds for me, I really appreciate it.