Instruction manual

• Certain materials such as:
- silicone
- silicates
- lead-containing compounds such as leaded gasoline
- hydrogen sulfide (H2S) above 50 ppm for one minute
or any exposure over 200 ppm
tend to desensitize the combustible gas sensor, thereby
giving erroneously low readings. Calibration checks must be
made frequently if such materials are suspected to be
present in the tested atmosphere; otherwise, the instrument
may give false readings and endanger life or health.
• It is important that such information obtained with the instrument
be appraised by someone skilled or experienced in interpreting
the instrument reading intelligently in the light of environment,
industrial practice, and exposure. For example, an atmosphere
that is indicated as non-hazardous from the standpoint of fire
and explosion may, if inhaled, be toxic to workmen who are
exposed for some time. Similarly, a vessel which is safe before
work is started may be rendered explosive by future operations
(for example, stirring or handling bottom sludge in a petroleum
storage tank). The latter example indicates the need for
frequently repeated or continuous tests of questionable spaces
while work is in progress.
The instrument will respond to those concentrations of gases or
vapors which are presented to the sensors. If the combustible is
a high boiling point solvent and is tested at normal ambient
temperature, a relatively low vapor concentration will be
shown by the instrument. If the container holding such
solvents is subsequently heated as by welding and soldering, it
is to be expected that the vapor concentration will increase, and
thus the atmosphere of a vessel which was originally shown
to contain only a low concentration of vapors may be
rendered explosive.
If an attempt is made to use such instruments for testing
atmospheres contaminated with high boiling point solvents
where the questionable space is at a higher temperature than
the instrument, it can be anticipated that there may be some
condensation of the combustible vapors in the sampling line
and in the flow system of the instrument if used; as a
consequence, the instrument may indicate less than the true
Chapter 1, Safety and General Limitations Instruction Manual
1-2 FiveStar Alarm