Teledyne 2240 – Portable Handheld Hydrogen Leak Detector, 2nd generation - Manual (Page 11)

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7. Hydrogen Sensing Considerations
From any given source, hydrogen gas disperses rapidly and
generally upward due to the very low density of hydrogen
compared to air. Understanding this behavior allows the
operator to more effectively search for hydrogen leaks.
Detecting hydrogen, due to its buoyancy, is not an exact
science. If the sensor element is near (and above) the leak,
the signal will be stronger but may be hard to locate due to
the small stream diameter. The stream diameter increases
farther away (higher) from the leak, but the concentration
decreases. Generally, greater distance will increase the
chance of intercepting the leak stream, but if the sensor is too
far away, the response will be too weak to detect.
As necessary, use the Wand Assembly to locate the Sensor
Module closer to the suspected leak area.
When drafts or air currents are present, the hydrogen will
tend to be dispersed by these forces. Testing for hydrogen
leaks downwind of the leak area will increase the chance
of detecting the leak.
If the hydrogen is rising in an enclosed building – where
there typically is a layer of warmer air near the ceiling -- the
hot air near the ceiling will have a lower density and may act
to retard the hydrogen from continuing to rise as rapidly in
lower layers of air. Thus, sensing hydrogen near ceiling
areas with high temperatures present may not be as
effective.
Low temperatures can also affect the behavior of
hydrogen. Hydrogen gas stored in a liquid state is at an
extremely low temperature. The low temperature of any
escaping gas will be of a higher than normal density and may
initially move downward. As the hydrogen gas 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.
After removing the handheld detector away from a leak,
the operator may see that the length of time from detecting
above approximately 1% hydrogen to indicating zero
hydrogen on the LCD display may be several minutes.
Page 22 of 26 M2240 R0
To improve this recovery time, a user activated reset
function has been incorporated. This function should be
used if the operator has located a leak and is trying to find a
new leak. To reset the unit follow the instructions in section
5 under Reset Mode.