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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