Soldering is a joining process used to join different types of metal together by melting solder. The solder traditionally used was made from tin and lead which would be melted using a soldering iron. It is well established that lead is a highly toxic metal with various adverse health effects. Since 1st July 2006, the majority of lead soldering has been banned in Europe by the EU directive commonly referred to as the Restriction of Hazardous Substances Directive (RoHS).
This was largely due to reducing the amount of discarded lead into the environment during the disposal of electronic components, rather than the risk of inhalation exposure during soldering. The risk of inhalation exposure to lead during soldering was actually quite insignificant due to the low temperature of the soldering iron compared to the higher fuming temperature of the lead.
The main health hazard from soldering is the fume produced from the flux, which usually contains colophony/rosin and is typically found in the soldering wire. Rosin-based solder flux fume is a notorious respiratory sensitiser and one of the main causes of occupational asthma is the UK.
Contact with this solder fume and its residues can also cause skin problems such as dermatitis. This has resulted in both a low long and short-term workplace exposure limits (WELs) with a ‘Sen’ notation (meaning Sensitiser) within the ‘EH40/2005 Workplace exposure limits’, as shown below.
Source: EH40/2005 Workplace exposure limits
How do we control inhalation exposure soldering fume?
The best way to prevent exposure to solder fume is by eliminating it altogether! However, as we don’t live in an ideal world, this isn’t usually possible. We can also try using a rosin-free flux, although these can often still produce a harmful fume. To reduce the amount of fume produced, the soldering temperature can be reduced but residual fume will still be present. Therefore, the most effective control is likely to be local exhaust ventilation (LEV), a method of extracting the fume away from the employee carrying out the soldering, before they breath it in. LEV suitable in controlling solder fume can come in various forms:
Capture Hoods – this commonly found control approach relies on the effective positioning of the hood in close proximity to the process. The ability to capture solder fume rapidly decreases the further the hood is away from the process. Since positioning the capture hood suitably close to the process can obstruct the operator’s work, these types of hoods are often ineffective at controlling exposure.
Low Volume High Velocity (LVHV) – this form of extraction attempts to capture the fume close to the source using small diameter ducting. The benefit of this design is that a low volume of air is required to produce a high velocity (LVHV), reducing the requirements of the air mover. Whilst this extraction is designed to be positioned near the tip of the soldering iron, in practice the operators seldom have it positioned close enough. Similar to capture hoods, the operators report the extraction obstructs their work.
Downdraught Bench – As the entire surface of the bench is under extraction, there is a large working area for the operator, mitigating the issue of suitable positioning. However, as there is such a large area, it means there is a large airflow requirement that increases the cost of the unit. Furthermore, certain shapes of components can block the airflow movement, reducing capture efficiency.
Partial Enclosures – this design works on the basis that the process is carried out within the confines of the enclosure. Provided there is sufficient airflow, the contaminated should be contained within the enclosure until it is ultimately extracted away.
How do we measure soldering fume exposure?
As discussed in a previous blog (Exposure Monitoring), there are many ways to monitor exposures and various reasons as to why you would want to, including a legal requirement in certain circumstances. When measuring exposure to hazardous substances, it is imperative to ensure the methodology is sound and reliable. In the UK, the Health and Safety Executive (HSE) provides a series of procedures for the measurement of personal exposure to contaminants in air, know as ‘Methods for the Determination of Hazardous Substances (MDHS).
MDHS 14/4 is a commonly used method, suitable for the measurement of exposure to most aerosols in the workplace. For particular processes such as soldering, welding and isocyanates, this not suitable. Due to this, specific methods have been written for these work processes. To measure solder fume, the HSE produced MDHS 83/3 Resin acids in rosin (colophony) solder flux fume: Laboratory method using gas chromatography (PDF).
The key difference between these methods, is the positioning of the sampler. MDHS 14/4 specifies the sampler should be attached to the worker’s upper chest or lapel, not more than 30 cm away from the nose-mouth region. MDHS 83/3 specifies to attach the sampling head containing the filter to the worker as shown in the figure shown below, positioning the sampling head on the right side for right-handed workers and the left side for left-handed workers. This is due the buoyant, narrowly rising fume and operative’s body positioning whilst soldering.
