FUMES AND FLUXES
The creation of a joint between either the faces of sheet metal components or
between wires and terminals using molten solder with a flux. Soft solder is an alloy of
tin and lead with traces of other metals. The flux may be in cores in the solder or
supplied as a liquid or jelly. The most common materials are:
rosin (also called colophony) - a compound which decomposes at high
halides, eg, ammonium chloride and zinc chloride (‘active fluxes’).
Newer fluxes (eg, Multicore Ecosol 105 or Omega) are based on organic acids.
There is an increasing use of lead free solder and it is likely that solder containing
lead will be phased out.
Lead fumes, especially to the unborn child (R61, 62, 20/22, 50/53), ammonium
chloride (if swallowed) (R22, 36) and zinc chloride fumes (R22, 34, 50/53) are
Fluxes containing zinc chloride can cause burns.
Flux can spit when heated. Small lumps of solder can be flicked off the tip of the
Flux fumes are irritant to eyes and respiratory system, possibly causing occupational
Fumes from rosin fluxes (Sen) can give rise to sensitisation of the airways.
Lead vapour is not generated significantly at temperatures below 500 °C.
Soft solders melt below 300 °C so the risk from lead vapour is negligible.
The fumes of ammonium chloride (WEL 20 mg/m 3 ) 1 and of zinc chloride
(WEL 2 mg/m 3 ) will not reach these 15 min reference values in a school workshop.
Active fluxes must be kept off the skin and out of eyes.
Instances have been reported of flux ‘spitting’ and entering the eye. There have also
been instances of small balls of solder being flicked off the tip of the soldering iron
when it is replaced in the stand although the risk is not great.
Fumes from heating any flux may irritate the eyes and respiratory system at high
concentrations. The fumes from decomposition of rosin flux have WEL values of
0.05 mg/m 3 (8 h TWA) and 0.15 mg/m 3 (15 min ref period). The concentration of
fumes must therefore be kept as low as reasonably practicable.
Since sensitisation can occur at very low concentrations, rosin-based fluxes should
be avoided altogether.
Eye protection 2 and gloves are required when using active fluxes and eye protection
should be worn when any soldering is done.
When using rosin-free (colophony-free) fluxes, ventilation produced by opening
windows near the working area will normally be sufficient to control the fumes.
If work with rosin flux continues, local exhaust ventilation will be required.
The only way of controlling the sensitisation risk is to stop using rosin-based fluxes.
Simple protective spectacles should be adequate.
© CLEAPSS 2009
Heat Processes: Soft Soldering, Fumes and Fluxes (Continued)
Contact an authorised waste disposal company if large quantities are involved.
Active flux should be stored in the container in which it is supplied, tightly closed, and
in a cool, dry, well-ventilated area.
It has been suggested that joints made in electronics work with rosin-based fluxes
last much longer than the period claimed for rosin-free fluxes. This is no longer true
and there is no need to use rosin-based fluxes and LEV even for repair work in
education establishments. The cost of providing LEV for student work-stations is not
usually justified since the extra cost of providing rosin-free solder is relatively small.
Lead free solder melts at a higher temperature (217 °C) than solder containing lead
and requires a soldering iron that will reach this temperature.
Where a person has become sensitive to the fumes from rosin flux, the slightest
exposure may give rise to an asthma attack.
IMMEDIATE REMEDIAL MEASURES
Active flux is swallowed
Fumes are inhaled
Active flux spilt on the skin
Active flux in the eyes
Active flux is spilt in
Burns to the skin
Serious burns to the skin
Seek medical aid.
Remove from exposure. Keep warm and at rest. Obtain medical attention.
Immediately wash the affected area with plenty of soap and water.
Irrigate immediately with water for at least ten minutes, holding eyelids apart. Obtain
Contain the spill with sand, earth or any suitable absorbent. Transfer to a container
Cool the affected area under a running cold tap for ten minutes.
Send for an ambulance. Cool the affected area under a running cold tap for ten
minutes. Watch for difficulty in breathing or faintness. Gently remove jewellery or
watches that might be difficult to remove later if the limb swells. Apply a dry dressing
held in place by a cotton wool pad secured with a bandage or adhesive tape if the
ambulance has not yet arrived.
© CLEAPSS 2009