SAFETY--Potential Hazards from Exposure to Elemental Mercury and Mercury Salts

In Reply Refer To:                          July 8, 1982
EGS-Mail Stop 412


WATER RESOURCES DIVISION MEMORANDUM NO.  82.112

Subject: SAFETY--Potential Hazards from Exposure to Elemental Mercury
and Mercury Salts

Although most people know that elemental mercury and mercury salts are
virulent poisons, it is commonly presumed that the danger is from oral
ingestion.  However, mercury is extremely volatile and the vapors are
readily absorbed through the respiratory tract or unbroken skin.  Mercury
acts as a cumulative poison because the rate of elimination by body
functions is low.

If mercury is spilled in a gage house or field vehicle, concentrations
hundreds of times greater than the maximum allowable can be attained.  Air
saturated with elemental mercury vapor at 2O degrees C contain a concentration
which exceeds the maximum allowable concentration of 0.01 mg/m3 (milligrams
per cubic meter) by about 1250 times.  The saturation vapor concentration
increases with increasing temperature.  At 60 degrees C, the maximum allowable
concentration is exceeded by nearly 25,000 times.  Thus, mercury must be
handled with the utmost regard for airborne contamination.

According to the Hydrologic Instrumentation Facility (HIF), about 300 pounds
per year of elemental mercury is shipped to Districts for replacement of
mercury lost from bubble gages.  Another use of elemental mercury by WRD is
in thermometers, and to a lesser extent in mercury-filled barometers.  We
have no good estimate of how much elemental mercury is in storage or use by
WRD at this time.  WRD also uses mercury chloride in tablet form for
water-quality sample preservation.  Each tablet contains about 13
milligrams of mercuric chloride in a sodium chloride matrix.

Possible sources of exposure to mercury vapor include the following:

o Mercury spilled in a field vehicle or gage house will result in a
continuing source of vapor.  A drop or two of mercury can produce unsafe
conditions.  On a hot day the vapor concentration inside the vehicle or gage
house may greatly exceed safe levels.

o Mercury stored in metal or glass containers cannot pass through the
container walls, but when stored in certain plastic containers, including
polethylene bottles, the vapor can pass through the container walls to some
degree.  Mercury is shipped by HIF in polyethylene bottles.

There are, however, mitigating factors that also need to be considered.

o The concentrations that are attainable in a closed environment are reached
slowly.  In a partially- or well-ventilated environment the maximum vapor
concentration will be considerably lower than saturation.



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o The maximum concentration criteria are based on a lO-hour exposure.  There
are few situations where WRD fieldmen would have a continuous lO-hour
exposure to very high mercury-vapor concentrations.

Safety measures that should be inmediately instituted are as follows:

o Mercury and mercuric chloride should be stored in airtight metal containers.
  An easy solution is to store the plastic bottles of elemental mercury
and the preservative tablet packets in army surplus ammunition cans.
When used for storage these cans, which have airtight, rubber-gasketed lids,
should only be opened out of doors or in a fume hood.  Cans should be
labeled with an appropriate hazard warning.

o No manometers should be transported with mercury in them.

o Broken thermometers and waste mercury should also be stored in an airtight
metal container.  When necessary, the container can be shipped to the
nearest Central Laboratory for mercury recovery.  The disposal container
should also be labeled with an appropriate hazard warning.

o Before entering a gage house that is known or suspected to have been con-
taminated by mercury, field personnel should fan the door back and forth for
a minute or two to exchange the stagnant air with fresh air.  The time spent
in the ventilated gage house should result in negligible exposure because
the vapor concentration increases slowly.

o Special care should be taken to prevent contamination of vehicles.  They
are the most likely places for near-saturation conditions to exist.  Fanning
of doors or opening windows for the first few minutes after re-entering a
contaminated vehicle that has been parked in the sun should quickly remove
vapor-laden air.  Open windows, or operation of air conditioners or heaters
should keep air exchange at a maximum once the vehicle is underway.  The air
conditioner and heater should be operated in the "outside air" mode as
opposed to the "recirculate" mode.

o No special safety precautions are necessary for water samples that have
been preserved with tablets containing mercuric chloride beyond the normal
mercury recovery and disposal procedures presently being performed at the
Central Laboratories.

Please observe the above safety measures.


                                    Thomas A. Buchanan
                                    Assistant Chief Hydrologist
                                      for Operations
Distribution: A, B, S, FO, PO

Key Words:  Potential Hazards, Elemental Mercury, Mercury Salts, Mercury

"This memorandum does not supersede any existing memorandum."