In December 2012, the European Chemicals Agency (ECHA) listed nPB as ‘a Substance of Very High Concern (SVHC)’ and is now reviewing its future use. Depending on the outcome of the ECHA review, users may be required to reduce their fluid consumption volumes, or replace their existing nPB fluid within the time period that will be specified.

nPB is already a solvent classed as ‘Carcinogenic, Mutagenic or Reproductive Toxin’ (CMR) and the Solvent Emissions Directive 1999-13-EC (SED) restricts consumption to below 1t/annum. 

 

The SED requires that substances or preparations containing volatile organic compounds (VOCs) classified as CMRs, be replaced as far as possible by less harmful substances or preparations within the shortest time feasible. As a result, more organisations are looking at alternatives to nPB.

  

About nPB

nPB is used in a broad range of industrial applications which include precision cleaning and solder flux residue removal in electronic parts manufacturing.  It was first introduced back in the mid-1990s as a less toxic alternative to hydrochlorofluorocarbon solvents. The main driver was a move toward reducing the use of ozone-depleting substances. At that time there was insufficient information available to allow an accurate characterisation of its toxicity.

 

However, based on various studies conducted over the past 10 years, the original 200ppm 8h time weighted average exposure guideline for nPB has been gradually downgraded. Today, the exposure guideline has been established by the American Conference of Governmental Industrial Hygienists (ACGIH) at 10ppm. Furthermore, the California OSHA has a proposal to set the exposure guideline at 5ppm – a concentration that may be unachievable in vapour degreasing operations.

 

So, regardless of the ECHA’s review, nPB’s future does not look positive.  Readers may be asking why this matters right now: can’t they wait until the outcome of all this?  Of course, that’s one option, but it’s a risky one. The process of researching, evaluating, testing and trialling alternatives takes time. For companies handling precision components, there is too much at stake to take quick decisions not backed by thorough due diligence.

 

Alternatives

Safer alternatives to nPB-based degreasing include aqueous and semi-aqueous processes. One benefit of these processes is that they have a relatively safe health and environmental profile (although large volumes of contaminated liquids still need to be disposed of safely). However, the cleaning quality may not be sufficient for many applications, particularly where precision-components are involved. Also, the process can be difficult to maintain and drying can be time-consuming, with the risk of water stains. The typically high energy and waste water disposal costs are also downsides.

 

Other alternatives for metal degreasing include HFC-4310mee and HFC-365mfc-based cleaners. These have favourable properties to enable efficient cleaning and are low in toxicity but have relatively high Global Warming Potential (GWP) figures, which mean that under environmental legislation they are more likely to be considered for restrictions in the years to come. Also, under the requirements of (EC) No. 842/2006 operators are required to be certified as competent for systems using hydrochlorofluorocarbon (HFC) fluids.

 

Another option that companies are looking at is the use of hydro-fluoro ethers, usually abbreviated to as HFEs.  HFEs tick a number of boxes:  they aren’t classified as CMR solvents (so there is no risk of falling foul of that legislation, should it become more strict in the future); HFEs have zero-ozone depletion potential and low GWP; and some HFE-based mixtures can be used as ‘drop-in’ replacements to nPB, meaning that there is generally no need to replace existing cleaning equipment. 

 

Importantly, HFEs – which are already deployed in many large operations worldwide – do not compromise on quality of cleaning. Drying time is rapid and removal of residue is efficient. Any downsides? The initial investment may be higher, but there is anecdotal evidence that once in place, less cleaning fluid is needed compared to other solvents, particularly in open top cleaning tanks.

While replacing nPB does require time, effort and potentially investment, there are viable alternatives and ones which ultimately, can lead to improvements in cleaning processes, as well as addressing health and safety concerns.  The reality is that users may not be given any choice but to seek alternatives, so it makes sense to start looking at the available options sooner rather than later.