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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Brian Ellis <[log in to unmask]>
Date:
Sun, 6 Jan 2013 11:30:12 +0200
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1-Bromopropane (aka n-propyl bromide or nPB for short) is a popular 
solvent which came on the industrial market in 1996. Its main uses are 
metal cleaning, diluent for adhesives and dry cleaning garments, as well 
as for what concerns us most, defluxing electronics assemblies.

When it was first marketed, there was no data on toxicity, 
carcinogenicity, mutagenicity etc. The makers initially proposed that 
the limit of the substance in the air breathed by the workers was 500 
ppm, but this dropped rapidly to 200 ppm. This was the Operator Exposure 
Limit (OEL) and it was only a recommendation. One small French producer 
recommended 10 ppm. The US National Toxicity Program started work on it 
in the early 2000s but this is still ongoing. OSHA cannot issue a legal 
limit until the NTP have pronounced. In the early 2000s, anecdotal 
reports started coming out of neurological problems in workers exposed 
to the substance. The makers funded some animal tests and most of them 
dropped their recommendations to 100 ppm on early results 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 25 ppm, but one recommended 
the old 100 ppm. This is still valid today 
http://www.cleanersolutions.org/downloads/msds/592/Ensolv%20MSDS.pdf

 From the practical point of view, 100 ppm is fairly easy to control. 25 
ppm is at the limit of possible for defluxing in our industry, using 
ordinary state-of-the-art machines. There are so-called "zero-emission" 
machines available but they cost 3-5 times more than the ordinary ones 
and generally they can keep average exposure down to lower single digits 
if used correctly.

In Europe, nPB was classed as a VOC (exempt in the USA) and regulations 
for this limited its use to negligible amounts. However, the REACH 
programme has proposed labelling it as a reproductive toxin, but this 
has not yet been studied. I don't know for sure the situation in Japan, 
but I believe it is similar to the USA. 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) = OEL of 10 ppm. 
The ACGIH is a highly respected NGO but their values have no force of 
law and are only recommendations based on known science. However, many 
companies using chemicals do try to take notice of their 
recommendations. The ACGIH have recently put a cat among the pigeons in 
that they have given an advanced notice of a change in the TLV for nPB 
and the proposed draft value is 0.1 ppm, an unprecedented two whole 
orders of magnitude lower than the current TLV 
http://www.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 that 
0.1 ppm is impossible to respect under industrial conditions so, if this 
value became 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 new "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 personally have known 
cases of people, including a close friend, who 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 proved 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 modelling and analogical comparison with similar known 
substances. This limit may be slackened if tests and experience show it 
is safe to do so.

Brian has spake!

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