Teledyne 2240 – Portable Handheld Hydrogen Leak Detector, 3rd generation (updated 1/31/11) - Manual (Page 22)

Handheld Hydrogen Leak Detector Model 2240
Teledyne Analytical Instruments Page 22 of 30
6. Hydrogen Sensing Considerations
From any given source, hydrogen gas disperses rapidly
and generally upward due to its very low density compared
to air. Understanding this behavior allows a more effective
search for hydrogen leaks.
The hydrogen plume from a leak generally spreads in a
roughly conical shape that is easily disturbed by
environmental conditions. Certain conditions such as
pressure, temperature, and leak size may act together to
change the shape of the hydrogen plume from a cone to a
laser-like beam. This makes finding a leak more difficult.
If the sensor element is near (and above) the leak, the
concentration will likely be higher but the leak may be
difficult to locate. As hydrogen dissipates the
concentration decreases. Generally, greater distances will
increase the chance of intercepting the leak stream, but if
the sensor is too far away, the response may be too weak
to detect.
When drafts or air currents are present, hydrogen will tend
to be dispersed. Testing for hydrogen leaks downwind of
the leak area may increase the chance of detecting the
leak.
If hydrogen is rising in an enclosed building the hot air near
the ceiling may slow the hydrogen’s rise. Thus, sensing
hydrogen near ceiling areas with high temperatures
present may not be as effective as at a lower level.
Low temperatures can also affect the behavior of
hydrogen. Hydrogen stored in a liquid state is at an
extremely low temperature. The low temperature of any
escaping hydrogen will be of a higher than normal density
and may initially move downward. As the hydrogen warms,
it will begin to rise upward. When checking for a leak in
areas where liquid hydrogen is stored, check both above
and below the area of concern.