By workplace & process
The wisp of smoke from a soldering iron looks harmless. It is a top cause of occupational asthma, with a very low exposure limit and a real duty to extract at the tip.
The short answer
The thin curl of smoke from a soldering iron looks trivial, but rosin-based solder flux fume - historically called colophony fume - is one of the top causes of occupational asthma in the UK. Its workplace exposure limit is very low, precisely because it causes serious harm at small concentrations. That combination - minor appearance, major hazard - is exactly why electronics soldering carries a genuine local exhaust ventilation duty under COSHH.
The detail
When rosin-cored solder or rosin-based flux is heated - above roughly 183 degrees for lead-free solder, higher in flux applications - it releases colophony fume, a complex mix of resin-acid particulate and gases. Inhaled, it can cause occupational asthma, and once a worker is sensitised even very low levels of fume can trigger an attack. It also causes rhinitis, eye and upper-airway irritation and can contribute to dermatitis. In the UK it ranks among the top five causes of occupational asthma and the top ten causes of contact dermatitis.
Its workplace exposure limit reflects that seriousness: a long-term limit of 0.05 mg per cubic metre over eight hours and a short-term limit of 0.15 mg per cubic metre over fifteen minutes. Those are among the lowest limits you will meet, and they are set because no safe threshold for the critical effect - occupational asthma - has been identified. Switching to lead-free or low-colophony solder helps but does not remove the duty, and de-soldering old boards still releases the fume.
What it means for you
The control is extraction at source: tip extraction built into the iron, a flexible capture arm at the bench, or a fume-absorber unit, drawing the fume away before it reaches the operator's face. A thorough examination and test checks that this extraction is actually capturing at the tip or bench, that airflow matches the commissioning benchmark, and that filters and ducts are sound - at least every fourteen months.
The common failing is a capture arm parked too far from the joint, or tip extraction that has lost airflow, so the fume drifts straight up into the breathing zone of someone bent over the work. Given how low the exposure limit is and how easily sensitisation is triggered, keeping that capture proven and close to the source is what turns a nominal control into a real one.
The service behind the guide
We test tip and bench extraction against the low exposure limit for solder fume and report on capture, airflow and any remedial work needed.
Questions
Yes. Rosin-based solder flux fume, or colophony, is one of the top causes of occupational asthma in the UK. Once sensitised, a worker can react to very low levels of fume, and no safe threshold has been identified.
A long-term limit of 0.05 mg per cubic metre over eight hours and a short-term limit of 0.15 mg per cubic metre over fifteen minutes - among the lowest workplace exposure limits, set because it causes serious harm at small concentrations.
No. Switching to lead-free or low-colophony solder helps but does not remove the duty, and de-soldering old boards still releases colophony fume. Extraction is still required.
At source - tip extraction built into the iron, a flexible capture arm at the bench, or a fume-absorber unit - drawing the fume away before it reaches the operator's breathing zone.
At least every fourteen months under COSHH. The test checks that the extraction captures at the tip or bench and that airflow matches the commissioning benchmark.
Phoenix Duct Clean · by the numbers
We test tip and bench solder extraction against the low exposure limit it must meet and report clearly. Call or email to arrange a visit.