Owner manual

4 Safety
757 VA Computrace – Hardware
52
4.2 Safety considerations concerning mercury
4.2.1 Properties of mercury
The most important properties of mercury (Hg) are listed in the Table below. This
compilation allows the following summary:
•
Mercury is a
heavy metal
with a very high density and is
liquid
at room tem-
perature.
•
Mercury is mobile at room temperature and tends to
form drops
because of
its high surface tension. The surface tension is around 6 times greater than
that of water, Hg is thus not wetted by water.
•
Mercury has a relatively
high electrical conductivity
(at room temperature it
is only some 60 times lower than that of silver).
•
Mercury has a relatively
high vapor pressure
compared with other metals.
Mercury vapor is some seven times heavier than air (so that it sinks rapidly
and specifically to the floor).
•
The
odor threshold is very high
relative to the threshold limit value (TLV).
•
Air saturated with Hg vapor (which naturally does not occur in practice) con-
tains approximately 250 times the amount of Hg specified by the TLV at room
temperature.
Properties of mercury
Property Value Ref.
Density
ρ
(liquid mercury) 13.5451 g/cm
3
(at
Θ
= 0 ° C) [1]
Density
ρ
(mercury vapor) 8.959 g/dm
3
(at
Θ
= 0 ° C) [2]
Melting point
Θ
F
–38.86 ° C (at p
air
= 1.01325 bar) [3]
Melting enthalpy
∆
H
F
2.295 kJ/mol (at p
air
= 1.01325 bar) [3]
Boiling point
Θ
V
356.73 ° C (at p
air
= 1.01325 bar) [3]
Boiling enthalpy
∆
H
F
59.1 kJ/mol (at p
air
= 1.01325 bar) [3]
Vapor pressure p 0.0253 Pa (at
Θ
= 0 ° C)
0.17 Pa (at
Θ
= 20 ° C)
0.391 Pa (at
Θ
= 30 ° C)
0.81 Pa (at
Θ
= 40 ° C)
1.69 Pa (at
Θ
= 50 ° C)
[2, 4]
Mass concentration
ρ
in air
(after reaching equilibrium)
2.0 mg/m
3
(at
Θ
= 0 ° C)
13.6 mg/m
3
(at
Θ
= 20 ° C)
29.6 mg/m
3
(at
Θ
= 30 ° C)
62.7 mg/m
3
(at
Θ
= 40 ° C)
126 mg/m
3
(at
Θ
= 50 ° C)
[2, 4]
Evaporation rate 85 µg/h·cm
2
(at
Θ
= 25 ° C) [2]
Surface tension
σ
4.67·10
–3
N/cm (at
Θ
= 20 ° C) [5]
Electrical conductivity
κ
1.044·10
4
S/cm (at
Θ
= 20 ° C) [6]
Odor threshold 13 mg/m
3
[2]
Threshold limit value (TLV) for air
for mercury
for organic mercury com-
pounds (calculated as Hg)
0.1 mg/m
3
0.01 mg/m
3
[4, 7]
[2, 4, 7]