23
8.2.1.3
Special precautions for explosive gas detectors
Sensors are sensitive to certain poisons, which can reduce their sensitivity: emission of
silicone-containing vapours at concentrations > 10 ppm and chlorinated or sulphurous
products at concentrations > 100 ppm.
A lack of oxygen (< 15% O
2
) or over-oxygenation (> 23% O
2
) may cause under-measurement
(in the former case) or over-measurement (in the latter case).
Sensors must be located head downwards at installation or during maintenance work.
8.2.1.4
Response to other explosive gasses
It is recommended that the detector is calibrated using the gas to be measured. Users wishing to
calibrate the detector using a gas other that detected and factory-programmed should refer to the
following table, and use the recommended gas and corresponding coefficient.
Table 1 : Calibration Coefficients
Gas
Chemical
Formula
LEL
(%)
LSE
(%)
Flash
point
(°C)
Vapor
density
Coefficient
-
Calibration gas
CH4 (methane)
Coefficient
-
Calibration gas
H2 (Hydrogen)
Coefficient
- Calibration gas
C4H10 (Butane)
Coefficient
- Calibration gas
C5H12
(Pentane)
Ethyl acetate
C4H8O2
2,10 11,50
-4
3,0
1,65
1,35
0,90
0,80
Acetone
C3H6O
2,15 13,00
-18
2,1
1,65
1,35
0,90
0,80
Acetylene
C2H2
1,50
100
-18
0,9
2,35
1,90
1,25
1,15
Acrylic acid
C3H4O2
2,40 8,00
54
2,5
5,00
4,00
2,65
2,40
Butyl acrylate C7H12O2 1,20 8,00
37
4,4
3,50
2,80
1,85
1,70
Ethyl acrylate
C5H8O2
1,70 13,00
-2
3,5
3,05
2,45
1,65
1,50
Acrylonitrile
C3H3N
2,80 28,00
-1
1,8
1,45
1,20
0,80
0,70
Ammoniac
NH3
15,00 30,20 < -100
0,6
0,90
0,75
0,50
0,45
Benzene
C6H6
1,20 8,00
-11
2,7
4,00
3,20
2,15
1,90
1.3-
Butadiene
C4H6
1,40 16,30
-85
1,9
2,55
2,05
1,35
1,25
Butane
C4H10
1,50
8,50
-60
2,0
1,90
1,55
1,00
0,90
Butanol
(Butyl Alcool)
C4H10O
1,4
11,3
29
2,6
1,95
1,60
1,05
0,95
2 - Butanone
(MEK)
C4H8O
1,80 11,50
-4
2,5
3,90
3,15
2,10
1,90
Cyclohexane
C6H12
1,20 8,30
-17
2,9
2,00
1,60
1,10
1,00
Dimethylether
C2H6O
3,00 27,00
-41
1,6
1,80
1,45
0,95
0,90
Dodecane
C12H26
0,60 ~6,0
74
5,9
4,00
3,20
2,15
1,90
Ethane
C2H6
3,00 15,50
135
1,0
1,50
1,20
0,80
0,75
Ethanol
C2H6O
3,30 19,00
13
1,6
2,15
1,75
1,15
1,05
Ether
(Diethylether)
(C2H5)2O 1,70 36,00
-45
2,6
1,90
1,55
1,00
0,90
Ethylene
C2H4
2,70 34,00
- 135
1,0
1,65
1,35
0,90
0,80
LPG
Prop+But
1,65
~9,0
< -50
1,9
1,90
1,55
1,00
0,90
Diesel
Melange
0,60
~6,0
55
> 4
3,20
2,60
1,70
1,55
Natural Gas
CH4
5,00 15,00
-188
0,6
1,05
Heptane
C7H16
1,10
6,70
-4
3,5
2,20
1,80
1,20
1,05
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