Table of Contents
Advertisement
40
A.7
Cross sensitivity
Some sensors react against gases other than those for which they have been
designed. For instance, the carbon monoxide sensor will show a reading when
hydrogen is present.
The following table gives the major cross-sensitivity values for the given sensors.
Gas at 100ppm
Nitric oxide (NO)
Ethylene (C
H
2
Hydrogen (H
)
2
Sulphur dioxide (SO
Nitrogen dioxide (NO
Other gases can also cause small readings on the toxic gas sensors. Do not be
alarmed if the CO and H
combustible gases with the %LEL sensor. This is neither a positive nor a negative
identification. Treat the environment as toxic, and wear BA.
A.8
Temperature class
To be intrinsically safe in a particular atmosphere, the maximum temperature the
surface the Orion can reach must be less than the ignition temperature of the gas or
vapour.
With alkaline batteries fitted, the Orion is rated for temperature class T4 (including
T1, T2, and T3) for ambient operating temperatures up to 40
T1 and T2) for ambient operating temperatures between 40
Some gases with a low ignition temperature are listed in Table A.3.
Table A.3: Some gases with low ignition temperatures
Gas or vapour
Carbon disulphide (CS
Acetaldehyde
Diethyl ether
Diethylene glycol dimethyl ether
Any gas or vapour with an ignition
temperature between 135
D.I.
Recommended Practice
FILE: W:\NB\RP HMRU\Orion\Frame Ver 02\Appendix.fm
Table A.2: Sensor cross-sensitivity
CO sensor reading
)
4
)
2
)
2
S sensors show small readings while detecting
2
Ignition
temp.
o
)
90
2
140
180
188
o
o
C and 200
C
H
S sensor reading
2
70 + 10 ppm
–
80 + 9 ppm
–
70 + 26 ppm
–
–
10 ± 3 ppm
–20 ± 2 ppm, or the sensor
2 + 6 ppm
failure reading of '- - -'
Temp.
Operational implication
class
C
T6
Always exit on reaching low LEL alarm.
o
C
T4
o
C
T4
For ambient operating temperatures
between 40
o
C
T4
reaching low LEL alarm.
T4
Version 02
Issued February 2011
© Copyright
State of NSW (Fire and Rescue NSW) 2011
Four-Head Gas Detector: MSA Orion
o
C, and T3 (including
o
o
C and 50
C.
o
o
C and 50
C, exit on
Hide quick links:
Advertisement
Table of Contents
