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MAN0530 Issue 15 - 07/17
2104M0506
APPENDIX B - GLOSSARY
Generally, gas readings of LEL.m (Lower Explosive Limit metres) are used. LEL.m is
calculated by multiplying the size of a gas cloud by its concentration.
An open path alarm set at 1 LEL.m would be triggered by any of the situations shown below:
100% LEL
LEL.m monitoring is particularly beneficial while the Excel gas detector is protecting the perimeter
of a plant or process, often reducing the quantity of point detectors required. The open path
LEL.m system has the ability to detect leaks that point detectors may miss due to prevailing
or changing wind directions, and can provide early warning of a dilute gas cloud when point
detectors may not register any gas presence.
To decide on alarm set points, it is recommended that the user firstly determine the size of gas
cloud that they wish to protect against, then set the alarm point to a fraction not greater than 60%
of that cloud size. For example, to protect against a 5 m cloud, set the alarm point ≤ 3 LELm.
B.3 ABBREVIATIONS
ATEX
CSA
DNV
DSP
EMC
FM
IAA
IECEx
1m
50% LEL
2m
10% LEL
10m
European Hazadous Area Approval
Canadian Standards Association
Det Norske Veritas
Digital Signal Processor
Electro-Magnetic Compatibility
Factory Mutual
Instrument Assisted Alignment
International Hazadous Area Approval
108
Searchline Excel
Calibrator
Type SHC1
ESC
Calibrator
Type SHC1
ESC
Calibrator
Type SHC1
ESC
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