Without effective control, solder fume rises vertically and, for manual operations, is likely to enter the breathing zone of the solderer. Rosin-based solder flux fume is now regarded as one of the most significant causes of occupational asthma in Britain.

Rosin-based fluxes may be integral with the solder or applied separately, as in liquid fluxes. For solder wire, commonly used in hand soldering, the flux is often contained in a central core and is released on heating.

Intermittent soldering work may lead to high, short-term exposures, particularly if carried out in an enclosed space or at an awkward angle. People maintaining and cleaning soldering equipment and control systems may also be at risk.