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Soldering: Occupational Exposure to Process Fumes

Exposure to solder fumes can cause occupational asthma. The likelihood of becoming sensitised to solder flux fumes can be high if suitable and sufficient controls are not implemented.

Introduction to Soldering

Soldering is a process that is similar to brazing. Essentially, metal components are joined together by heating and then melting a filler metal or alloy combined with a flux that flows into a joint. The filler then cools and forms a join between the two components.

Soldering is undertaken at temperatures below 450 degrees celsius. Unlike brazing, which is undertaken at temperatures above this. Health hazards can vary, depending on the materials used within the process. Similar to welding whereby various consumables are used depending on the types of metals being welded or characteristics of the welds required to meet a set of specific standards. Soldering isn't too dissimilar in this instance.

Soft soldering, using lead and tin alloy based solders is widely used throughout the electrical and electronics development/manufacturing industry. The material is used to make electrical connections.

Exposures and Common Health Effects

As soldering is undertaken at lower temperatures, metal fumes are generally not emitted in harmful quantities and therefore are usually of little concern. However, the main hazard exists in the break down of the flux which is commonly rosin-based. Rosin solder flux fume is a potent respiratory sensitiser.

Rosin is used because of its ability to clean surfaces, increase solder flow and can also prevent oxidisation. Rosin is a naturally occurring resinous material obtained from pine trees.

Health effects occur from the rosin breakdown at temperatures greater than 200 degrees Celcius. At these temperatures, rosin-based solder flux fumes are emitted. These contain a range of acidic resin particles and other gaseous components. It is said that between 250-400 degrees celsius, particulate fume can triple.

Inhalation of rosin-based solder flux fume can cause occupational asthma. The BOHS reported that the substance is one of the leading causes of occupational asthma in the industry, of which the effects are permanent and irreversible. Small quantities can cause an asthma attack and further prevent the affected person from working with the substance in the future as they become sensitised.

Exposure can cause irritation to the eyes and upper respiratory tract in addition to occupational asthma. It's important to note that it has not been possible to identify a safe level of exposure below which occupational asthma will not occur. Exposures should, be reduced to as low as reasonably practicable or avoided entirely.

Fumes will rise vertically into the operator's breathing zone should suitable and effective controls not be in place. Therefore, if the substance is not captured at source, a build-up of the contaminant could directly expose the worker and others working in the same area. Adequate control often requires the use of local exhaust ventilation.

Plumbing and Gas Fitting

Soldering is also undertaken in the Plumbing and Gas Installation Industry. The use of gas torches can raise temperatures to levels which are high enough to produce lead fume. The use of lead-free solders is sometimes required. However, a breakdown of the flux would still place workers at risk of respiratory sensitisation.

Control Measures

Where LEV is impracticable, other control measures should be considered to minimise or prevent exposures. Respiratory protective equipment can be used as a secondary control measure should the possibility of being exposed still pose a foreseeable risk to health even with other controls in place.

Workplace exposure monitoring can be undertaken as part of your safety management system implementation. Workplace air monitoring can be used to check the effectiveness of current control measures and should be carried out by a competent occupational hygienist who will utilise an approved sampling method to determine airborne concentrations and personal exposures.

Routine health surveillance should be undertaken. For example, anyone likely to be exposed to rosin-based solder flux fume should partake in a routine health surveillance program in which spirometry is undertaken to determine lung function.

Do You Need Support with COSHH?

It is hoped that this article goes some way to providing a brief overview of COSHH. If you wish to know more on this subject or need support with your COSHH assessments, exposure monitoring or the testing of your LEV systems, RPE Fit Testing then please feel free to get in touch with us through social media or our website (, by email at or simply give us a call on 01709 931299.

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