No. 104 - Miljøstyrelsen

48
In practice, thus, a maximum of 0.5 % of total quantities of mercury will
evaporate momentarily and in the subsequent 30 minutes up to around 10 %
of total quantities of mercury in the lamp will evaporate (7 % already after a
few minutes). For the worst-case calculations it is assumed, however, that the
10 % of the total mercury amounts will evaporate immediately when the lamp
breaks.
Duration of exposure t
It is assumed that the cleaning scenario in the worst case lasts 30 minutes and
that the person is exposed to the same concentration of mercury for all 30
minutes - corresponding to the initial concentration at the time 0. It is
assumed for the long-term exposure that in the worst case it will be 24 hours
per day in order to take into account homebound persons.
Volume of room Vroom It is stated in the ECHA Guidance Chapter R.15 (2008) that for short-term
local exposure the volume of a room can be set at 2 m 3
in order to represent
the air immediately surrounding the exposed person. This value is used as the
only value for the cleaning scenarios since mercury vapours are heavy, and the
concentration of mercury in a room will be unevenly distributed where most
mercury is found nearest to the place of breakage. According to, among
others, Stahler et al. (2008) the concentration of mercury will be larger in, for
example, 30 cm’s height than in 1.5 metre’s height. Thus, it will give an
incorrect picture to “dilute” the mercury concentration on the entire volume
of the room.
The 2 m 3 immediately next to the exposed person can thus also be used as an
estimate for the concentration in the lower 30-50 cm from the floor
surrounding the place of the accident.
Ventilation A of room
The concentration of mercury in the room is calculated for three different
rates of ventilation: No ventilation, normal ventilation and ventilation with all
windows and doors open. No ventilation means an air exchange rate of zero
and corresponds to a fictitive situation where the concentration is constant in
the period of time applied. Normal ventilation is defined by the Danish
Environmental Protection Agency as 0.6 times per hour. According to the
ECHA Guidance Chapter R.15 (2008) air exchange in a room with all
windows and doors open is at either 4.2 or 6.2 times per hour. Here, the most
conservative value of 4.2 times per hour is used.
Thus, the following values for ventilation of the room are used:
� No ventilation – corresponding to 0 m 3
/min (note that this is a fictive
value, since there will always be minor leaks in a house).
� Normal ventilation – corresponding to 0.02 m 3 /min for a volume of 2
m 3
(room size x air exchange per hour / 60 minutes).
� Strong ventilation (all windows and doors open) – corresponding to
0.14 m 3 /min for a volume of 2 m 3 (room size x air exchange per hour /
60 minutes).