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What follows is a lift from
http://acc6.its.brooklyn.cuny.edu/~scintech/mercury/WhatBigDeal.htm .
[m^3 means cubic meter]

"VC = S-Q   [I think this equation is a little fuzzy]

Where V is the room volume in cubic meters (m^3), C is the
concentration in micrograms per hour, and Q is the air flow
rate from the room in m^3. S, the mercury evaporation rate,
is the rate of mercury vaporization per unit area of
mercury. This is a constant value of 7 ug/cm^2/hour at
20*C."

The Agency for Toxic Substances and Disease Registry
(ASTDR)'s minimal risk level (MRL) for mercury vapor
inhalation is .3 ug/m^3. This is an estimate of the daily
human exposure that will most likely not result in risk. The
occupational exposure limit set by the U.S. National
Institute for Occupational Safety and Health is 50 ug/m^3."


Here's a simple example, use a 6 cm X 10 cm mercury horizon
for one hour in a 5m X 5m X 4m room at 20 degrees C with a 2
m^3 per hour ventilation.

The mercury lost from the horizon equals (7 ug/cm^2/hr) X
(6cm X 10cm)             =420 ug/hr into a (5 X 5 X 4m) room
with a 2 m^3/hour turnover of air

         = 420 ug/hr /(100-2) m^3 = 4.2ug/m^3/hr.

If left for 12 hours, the concentration builds to 50.4
ug/m^3 , i.e.. the occupational exposure limit.

Conclusion: Keep the mercury container in a sealed flask
indoors, fill and use the horizon outdoors. If you inhaled
ALL of the evaporation of mercury from a 6cm X 10 cm horizon
for six minutes out of every hour while taking sights, you
would still not exceed the occupational limits. Thus,
personal exposure will be well within safe limits.

Did I get it right?
Peter Ifland
P.S. Thanks to Paul Hirose for pointing us to a very
informative site.

   

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