New Exposure Recommendations on nPB Will Mandate Change for Most Users

Tue, 04/22/2014 - 2:11pm
David Ferguson, Senior Market and Technical Manager, MicroCare Medical

Normal propyl bromide (nPB) has become a popular solvent in the last 15 years. It is commonly found in inks, coatings, as a dry cleaning fluid and as a metal cleaning solvent.

Its popularity arose due to its high solvency and lack of regulatory restraint. Introduced after the publication of the National Emission Standards for Hazardous Air Pollutants (NESHAP) standards, it was identified as an easy replacement for Trichloroethylene (TCE) and 1,1,1 Trichloroethane (TCA) in the above applications, along with many others. It is a non-flammable, high boiling solvent that is effective in cleaning many soils, including heavy greases, waxes and flux residues from electronic assembly.

The United States Environmental Protection Agency (EPA) initially approved nPB for use as a solvent, and conditionally approved it as a carrier fluid for inks and coatings; but it was not approved in aerosol formulations due to the higher exposure levels from being dispensed openly from a can. Last year, the EPA stated that they were reviewing nPB, and may revoke its approval as a carrier solvent in inks and coatings due to high levels of exposure from the process and from growing documentation that nPB may be a reproductive carcinogen.

On March 1, 2014, the American Council of Government and Industrial Hygienists (ACGIH) completed its second extended review of the toxicity studies of nPB and confirmed that it does cause extensive reproductive harm in both rats and mice, and that the findings transcend to humans. As part of their findings, the ACGIH published a reduction in their recommended Permissible Exposure Limit (PEL) on nPB from 10 parts per million (ppm) to 0.1 ppm for an eight-hour time weighted average (TWA). At the time of the writing of this, the EPA had not commented on this report. The EPA’s Allowable Exposure Limit (AEL) for nPB is still 25 ppm (non-enforceable) eight-hour TWA. (Note: the government sets AELs’ and PEL’s are established by the manufacturer or outside agency.) The EPA no longer issues AEL’s for new molecules unless EPA feels that a federal guideline is necessary. Thus, you may find numerous newer solvents with only PEL’s. Check to make sure the molecule is EPA Significant New Alternatives Program (SNAP) approved. This will confirm the EPA has authorized its use as a cleaning, carrier, aerosol or coating fluid.

How Does this Report Affect the Industry?
While the ACGIH report will not trigger an OSHA enforcement action, their findings are considered to be accurate and methodical. More importantly, their studies are cited in the formation of legislation and in the courts on matters regarding chemical safety and worker exposure.

From a market standpoint, the Department of Defense immediately acted on this announcement and instructed all military installations and operations to transition away from nPB in all of the cleaning operations. It is expected that this policy will transition to their primary suppliers.

What Should a Company Do if They Are Using nPB?
First, the company should review its processes to determine where it is using nPB and why. Most production facilities are using nPB as a cleaning solvent in applications noted above. nPB offers strong cleaning solvency, non-flammability and is fast drying. It’s also excellent at removing contaminants from blind holes or from under low stand-off components, such as highly populated electronics. But nPB is unstable in the presence of excess moisture and white metals and therefore needs stabilizers to keep it from going acidic. nPB is more prone to going acidic then TCE or TCA, so operators need to be diligent with routine stabilization testing. Otherwise, the nPB would become acidic in a very short period of time.

Next, current facilities using nPB should research chemical suppliers to find companies offering safer, replacement solvents – preferably ones that will operate in their current cleaning process without modification. Try to find a supplier who offers more than one alternative, as the one-size-fits-all solvents no longer exist. Choosing a supplier with a limited offering may not give you a solvent with all the attributes you need to continue to clean your components to your customer’s satisfaction. Also, look for chemistries that do not require stabilizers and that are non-flammable. This transition should allow for improvements, but not introduce additional constraints. A supplier that offers a full laboratory and can test clean your parts would also be beneficial so you can minimize the transition time in production.

There are several dozen non-flammable, stable, vapor-degreasing solvents available that have PEL’s near or above 200 ppm. Research your options and choose a solvent supplier who also offers field support. The transition will be smoother if you have an industry specialist review your equipment and process. Someone who is trained in the business of precision cleaning may spot a detail or constraint that would affect a seamless conversion.

What Does this Announcement Mean?
The report will not affect the availability of nPB for cleaning and carrier applications until the EPA states otherwise. However, the report does provide strong evidence that other fluids should be considered for industrial applications over nPB, and that current users of nPB should address a solvent change as quickly as possible.

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