No. 104 - Miljøstyrelsen

32
cleaning after an accident. Therefore it is assumed that 10 % of the total
amount of mercury evaporates in 30 minutes in the exposure calculations.
Thus, in practice a maximum of 0.5 % of the total amount of mercury will
presumably evaporate momentarily after which in the following minutes up to
7 % of the total amount of mercury contained in the lamp will evaporate and
up to 10 % after 30 minutes. In the worst-case calculations it is therefore
assumed that 10 % of the total amount of mercury will evaporate immediately
when the lamp breaks.
A number of measured values show that maximum concentrations can easily
exceed the occupational threshold limit value – even with a very high factor.
These maximum values, however, are only present for a brief period of time.
Both calculation models and tests show that the concentration of mercury
decreases very quickly to low levels far below relevant limit values through
continuous ventilation of the room.
Tests also show that concentrations of mercury are higher 30 cm above floor
height than 1.5 m above floor height. In addition to the height above floor
level the concentration of mercury in the room after breakage of a lamp
depends on the quantities of mercury in the lamp and, possibly, the form in
which mercury is present in the lamp.
In one study a certain concern is expressed for postponing cleaning after
breakage of a compact fluorescent lamp, since three different tests with the
same broken lamp showed that a long waiting time (46 minutes) compared
with a short period of time (1 minute) before cleaning up resulted in higher
average concentrations (both in 30 cm’s and in 1.5 metre’s height) – despite
the fact that a window was opened immediately after the accident in all three
cases. Due to the high concentrations measured immediately after the
breakage (up to 0.05 mg Hg/m 3
) it is recommended in the study to put off
cleaning for a few minutes – some 5-15 minutes, but no longer than that.
Furthermore, tests have shown that in a room cleaned after an accident and
where visible residues of the fluorescent lamp and mercury have been
removed, concentrations of mercury can exceed the USEPA RfC value
(reference concentration without harmful effects) for short periods of time
during and after vacuuming: tests show that when floors containing mercury
residues are impacted physically, concentrations at floor height may increase
substantially.
Particularly carpets seem to contain more ”mercury residues” after cleaning
compared with a smooth wooden laminate floor. Old wooden floors with large
spaces may, however, be just as difficult to clean as a carpet.
A vacuum cleaner can easily be contaminated with mercury if it is used to
vacuum glass residues from the fluorescent lamp and thereby release mercury
vapours to the indoor climate for a long period of time.
One of the interviewed manufacturers stated that during an accident it is
relevant to remove all visible glass, powder and even droplets of pure
mercury. Both glass and powder contain mercury.
Several references state that the broken lamp should be removed using
materials that are subsequently discarded, i.e. use cardboard pieces to pick up