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Soldering - An example of a hazardous process

HSE statistics (2004/05) showing incidence rates of occupational asthma reported by chest physicians puts rosin based solder flux fume in the top ten.

Occupational asthma is an allergic reaction that can occur in some people when they are exposed to certain substances in the workplace, for example solder fume. These substances are called 'respiratory sensitizers' or asthmagens. They can cause a change in people's airways, known as the 'hypersensitive state'. Not everyone who becomes sensitized goes on to get asthma. But once the lungs become hypersensitive, further exposure to the substance, even at quite low levels, may trigger an attack.

Early symptoms from fume exposure can include:

  • watering, prickly eyes
  • running or blocked nose
  • sore throat
  • coughing, wheezing, tight chest and breathlessness

Rosin based solder flux fume is generated when rosin based solder flux is heated. During hand soldering the fume rises vertically on thermal currents created by the heat of the iron, entering the breathing zone of the worker as they lean over their work. The quantity of fume emitted will depend on a number of variables including: the rosin content; the solder temperature; and the size, spread and number of joints being worked.

Assuming substitution is not possible and the lowest rosin content solder flux for the job has been selected the main emphasis is to optimize the solder temperature and to provide effective fume extraction. Solder machines should always be enclosed and extracted. Whilst for hand soldering the extraction control solutions will depend on:

  • soldering temperature
  • soldering time
  • size, spread and number of joints being worked
  • shape of the workpiece
  • size of the work area
  • number of people soldering per period

Rosin based solder flux fume (RBSFF) is a hazardous substance under COSHH 2002 (as amended) and has been assigned both a "sen" notation and a "skin" notation indicating it is capable of causing both occupational asthma and skin sensitization. RBSFF has Work Place Exposure Limits (WELs) of:

  • 0.05 mg/m3-8 Hr time weighed average (full shift exposure averaged over eight hours) and
  • 0.15 mg/m3-15 minute TWA (15-minute reference period)