Detector Location - GasTech D-Guard2 Operator's Manual

9.5.2

Detector Location

Although over time, gas released into a space will expand to uniformly fill it with equal concentration, in many
practical applications, there exists the possibility of pooling due to areas that have little or no ventilation or
natural movement of air. For these locations higher than average concentrations of any gases present may exist
since natural diffusion could well be a slower process compared to the rate at which gas is entering the area. In
working environments where there is a likelihood of these situations occurring, proper consideration to the
location of gas detection instruments is important.
The specifics as to what constitutes the ideal location for gas detectors are strongly dictated by the actual
physical makeup of the environment. Considerations could be for example: - likely points of release, location of
personnel in relation to points of release, ventilation characteristics, temperature, volume of space in and
around personnel (open or confined space) and maximum time durations for exposure to any released gases.
Knowing the characteristics of the gases to be monitored can assist in deciding on optimal locations. Permissible
exposure levels are covered by various health and safety standards and are not reproduced in this manual.
A characteristic of significant interest is the buoyancy of the gas in air, essentially whether it is more or less
dense than air. Knowing this can provide some indication of areas of possible pooling or areas near a point of
release that leaked gas will initially move towards.
Gas Density (kg/m
Air
Ammonia
Carbon Monoxide
Chlorine
Ethylene Oxide
Fluorine
Hydrogen
Hydrogen Chloride
Hydrogen Cyanide
Hydrogen Sulphide
Nitrogen Dioxide
Nitric Oxide
Ozone
Phosphine
Sulphur Dioxide
Oxygen
Methane
Carbon Dioxide
Table 2: Absolute and Relative Densities of Common Gases Referenced Against Air.
* Absolute densities are given at STP 101.3kPa / 15⁰C unless otherwise noted
3
) @ STP 101.3kPA/15⁰C
1.225
0.7289
1.1849
3.04
1.8375 (101.3kPa / 20⁰C)
1.6074
0.0852
1.56
1.15
1.4534
3.21
1.3402 (101.3kPa / 0⁰C)
2.154 (101.3kPa / 0⁰C)
1.45
2.7633
1.354
0.6797
1.8714
20
Relative Density (Air = 1.0) Heavier or Lighter Than Air
1.0
0.595
0.967
2.480
1.52
1.312
0.0695
1.274
0.94
1.186
2.62
1.094
1.758
1.184
2.256
1.105
0.555
1.53
2
D-Guard
-
Lighter
Lighter
Heavier
Heavier
Heavier
Lighter
Heavier
Lighter
Heavier
Heavier
Heavier
Heavier
Heavier
Heavier
Heavier
Lighter
Heavier