Document B8Bagnxr1B08jNLa4VpQ1XJ1L
ABD00238572
To:
Interoffice Communication
From: Date:
Subject:
MGtt
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AprjJU-2^, 1992
o2 Monitor Conclusions and Recommendations
VISTA
False alarms from the ambient air oxygen monitors in the inert gas generation room in P-1 has resulted in questionable safe work habits.
Recommendations To correct the situation the following steps should be taken.
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Schedule regular monthly recalibration of all
oxygen monitors. Replace all of the cells
annually.
Calibration instructions are
included with the attached operating
procedures.
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2. Retrain I&TT pevtonnol and personnel working in
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affected areas to safely respond to alarms as outlined in the original oxygen monitor operating procedures.
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3 . Maintain specific records of cell replacements. These would include the exact
sensor replaced.
Exact records of cell
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replacements will allow future analysis of the
performance of cells in different areas of the
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Discussion Several factors may cause false alarms including
^ incorrect fuel cell type, ambient air contaminates, and
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improper maintenance.
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The fuel cell now in use is a class B-3 from Teledyne Instruments. The manufacturer recommends this cell for personnel protection service due to a 13 second response time and an expected life of 12 months. Halogens, lead compounds, HCl, S02, S03, and H2S will give false readings but are not present in significant amounts in P-1.
Work orders from the last year indicate 5 cell
replacements (resulting in costs of $793) and 3
instrument recalibrations.
If these records are
ABD00238573
complete, cell life in the 3 sensors in P-1 last an average of 7.2 months. This corresponds to an estimated life of 6 months by maintenance personnel. Work orders are generally not specific enough to tell which of the sensors failed.
The fuel cell output decreases with time eventually
resulting in incorrect readings. This decreasing output
might be the cause of most of the false alarms. The
drift is vaguely reported to be 1% of full scale over
weeks,
however,
the
manufacturer
recommends
recalibration of the meters every 2 to 4 weeks. There
is currently no schedule for regular recalibration.
With the data available, my conclusion is that the cells are performing at the manufacturers specifications. However, because of drift, the meters must be routinely recalibrated to adjust for the reduced cell output.
Michael G. McCollum Process Engineer
TRM