----- Original Message -----
Sent: Tuesday, May 11, 2010
9:29 AM
Subject: Re: [DCHAS-L] 3 re: Hg
response
It's clear from the discussion here that many just don't
appreciate the
nature of mercury, and that many of those commenting have never
actually
handled the material.
Permit me to address a few points:
1. Taking students to the hospital for "decontamination" was
over-reaction, absolutely yes. It was also the worst thing that
could
have been done if there was serious contamination. That would
have
spread the mess to the transport vehicles, the hospital, etc. etc.
etc..
2. The ability of mercury to "shatter" into tiny, tiny droplets
literally
increases its surface area by a factor of **one million** compared to
a single
small pool. This not only makes cleanup very difficult, it
makes the
evaporation rate increase by orders of magnitude. As one doesn't
know
the size and physical distribution of the droplets, any calculations
about how
long it would take to all evaporate is nothing more than complete
conjecture,
whether we're guessing at how long it would take all the mercury to
"go away"
or whether the concentrations would become dangerous.
3. Thus, discussion of whether mercury vapor would saturate in a
room is
a pointless paper exercise given the number of variables. It is
a
question whether the vapor concentration will begin to approach a
dangerous
level, a level which is well below saturation. The only way to
do that
is to measure the levels. And a measurement taken at the peak of
the
workday with high turnover will almost certainly differ from one taken
in the
morning after a night of low air turnover.
4. The (always reliable; roll eyes) media report that there were
3
contamination sites within the school, and it's obvious that one can't
simply
assume that those were the only ones,
http://www.poughkeepsiejournal.com/apps/pbcs.dll/article?AID=
20105110317
In any high-traffic area, the mercury will be spread far and
wide.
So if kids played with it in a cafeteria, then it was no doubt
tracked
throughout the school, although in a decreasing amount with respect to
distance from the original spill area. The article I just
referenced
mentions that the building went into lockdown, which is surprisingly
smart
with respect to determining which areas were contaminated and keeping
the
spilled material from being spread further.
5. Most attempts to sweep up mercury simply break it up into
smaller bits
and spread it around. And vacuuming is obviously out. We'd
expect
that the untrained personnel who first noticed the situation would
have tried
one of those two methods before HazMat was ever called . BTW,
sprinkling sulfur on spills is basically useless as the rate of
reaction of
solid sulfur with mercury is exceedingly slow. I have always
preferred
zinc powder, which amalgamates mercury quite well.
6. As mercury amalgamates with common metals with the
exception of
iron/steel, it can evaporate into the room, react with a desk,
lighting
fixture, soda machine, whatever, and then continue to pose a long-term
health
hazard. Again, air monitoring is the only way to determine if
the risk
is real.
In short, closing the school in order to a) ensure that the
extent and
amount of the spill was accurate determined, b) prevent further
distribution/spread of the mercury, and c) ensure that monitoring
results were
negative was a prudent precaution when dealing with an unknown level
of
hazard. Better to close it and find out afterward that the risk
was
minimal than to later find that the risk was real and
underestimated.
Rob Toreki
On May 11, 2010, at 7:43 AM, Ben Ruekberg wrote:
Not
wishing to be
disputatious concerning the hazards of mercury, nonetheless, I think
before
worrying about the saturation vapor pressure of mercury, I suspect
that one
should also consider the rate of evaporation of mercury as
well. I
don=92t know what it is, but were it all that significant people
would
probably have to have been refilling McLoed gauges with some
frequency. In fact, I don=92t recall that ever being
necessary, nor do I
recall finding significant amounts of mercury in the Nitrogen traps
of
vacuum systems under normal circumstances. Given that most
rooms have
reasonable air exchange, I suspect that rooms seldom reach
saturation.
To refer
to the
example of 5 mg of mercury reaching the saturation concentration of
15 mg
m^-3, one would be dealing with a room with a volume of 1/3 m^3, an
unusually small room. A 20=92 X 20=92 X 10=92 room would hold
(at
saturation, with no air exchange) ~ 1.6 g of mercury, a mere drop,
but if a
drop of mercury evaporated at a significant rate an amount that
might be
noticeable.
What I am
suggesting is that the rate of evaporation might be more important
than the
saturation vapor pressure and may reduce the hazard (at least for
the short
term) and that one might not need to be overly
alarmed.
Thank
you,
Ben
Date: May 11, 2010
5:26:29 AM
EDT
Subject: RE:
[DCHAS-L] 3 re:
Hg response
Please, don=92t
underestimate
the danger of mercury vapour!
Mercury vapour is
dangerous,
and it is difficult to clean up indoor spills completely. Even the 5
mg Hg
from a crushed light bulb indoors can create dangerous air
concentrations,
as many publications have shown. The saturated air concentration at
room
temperature is about 15 mg Hg/m3. That concentration is 500 times
higher
than the TLV, and such exposures have resulted in serious
intoxications.
Secretariat for
Metrology,
Chemical analysis and Management Systems
FORCE Technology,
Br=F8ndby
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