Why one solvents expert thinks we have the method for approving substances backwards.

The popular solvent known as 1-bromopropane (aka n-propyl bromide or nPB for short) came on the industrial market in 1996. Its main uses are metal cleaning, diluent for adhesives, dry-cleaning garments, and – most relevant to readers – defluxing electronics assemblies.

When it was first marketed, there were no data on toxicity, carcinogenicity, mutagenicity, and so on. The makers initially proposed a 500ppm limit of the substance in the air breathed by workers, but this was rapidly dropped to 200ppm. This was the Operator Exposure Limit (OEL), and it was only a recommendation. One small French producer recommended 10ppm. The US National Toxicity Program started work on it in the early 2000s, but this is still ongoing. OSHA cannot issue a permitted legal limit (PEL) until the NTP has finished. In the early 2000s, anecdotal reports started coming out, indicating neurological problems in some workers exposed to the substance. The makers funded some animal tests, and most of them dropped their recommendations to 100ppm in the mid-2000s after it was found that mice suffered longer nerve reactions in the CNS and lower sperm motility. Later results indicated that both the neurotoxicity and the reproductive toxicity were worse than thought, and most makers reduced their recommended OEL to 25ppm, although one recommended 100ppm. This is still valid today.

From the practical point of view, 100ppm is fairly easy to control. The limit of possible for defluxing in our industry is 25ppm using ordinary high-quality open-top machines. So-called “zero-emission” machines are available but cost three to five times more than conventional ones and generally can hold average exposure to lower single digits if used correctly.

In Europe, nPB was classed as a VOC (less regulated in the US), and the VOC Directive limited its use to negligible amounts. However, the REACH program has proposed labeling it as a reproductive toxin, but this has not yet been studied. In China, where vast amounts are made and used, the limit is pending.

About two years ago, the NTP issued an interim warning that animal tests on both rats and mice indicated a strong probability of carcinogenicity and mutagenicity. The American Conference of Government and Industrial Hygienists (ACGIH) issued a Threshold Limit Value (TLV), similar to the  OEL, of 10ppm. The ACGIH is a highly respected NGO, and its recommendations are based on known science, but it has no force of law. However, many companies using chemicals do try to take notice of its recommendations.

The ACGIH has recently put a cat among the pigeons in that it has given advanced notice of a change in the TLV for nPB. The proposed draft value is 0.1ppm, an unprecedented two whole orders of magnitude lower than the current TLV (acgih.org/store/ProductDetail.cfm?id=2151). I’m not yet aware of the reason behind this, but it must be serious.

Needless to say, 0.1ppm is impossible to respect under industrial conditions so, if this value were to become a legal limit, nPB would be condemned to death as an industrial solvent for defluxing, etc. (It is also used in small quantities as feedstock for the pharma industry in the manufacture of psychotropic drugs such as diazepam.)

Why this rant? Simply because I suggest we have it wrong, all wrong. Workers were initially exposed to what has been deemed potentially dangerous levels of nPB, up to 5,000 times higher than the proposed “safe limit.” Even today, one maker is recommending an OEL of 1,000 times the proposed OEL. This is far from the first time that workers have been told that such-and-such a chemical is safe, only to die prematurely from the effects of exposure 10, 20 or 30 years later; I know of cases, one involving a close friend, where people have died in their 50s and 60s from organ failures resulting from chemical exposure as young adults.

Yes, we say that chemicals are innocent until proven guilty. This is wrong, and I suggest that they should be considered guilty unless proven innocent. An arbitrary tight limit should be placed on new chemicals, based on computer modeling and analogical comparison with similar known substances. This limit may be slackened if tests and experience show it is safe to do so.

Brian Ellis is a retired consultant and longtime vice-chairman of the IPC Cleaning Handbook task group. He is author of Cleaning and Contamination of Electronics Components and Assemblies, among several other books and technical papers. He was a member on the Solvents Technical Options Committee of UNEP, advisory to the Parties of the Montreal Protocol, from 1989 to 2004, co-chaired the nPB Task Force and was Senior Solvents Consultant to the UNEP Multilateral Fund and to the Swiss Federal Office of the Environment. He founded Protonique SA and Protonique Ltd. and developed the Contaminometer, the Insulohmeter, the APL series of aqueous cleaners and driers and other equipment; bne@bnellis.eu.

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