Dear Colleagues, dear Ken,
I owe you an apology for not summarizing the results of my earlier call
for information Advice on Oxygen sensors, please earlier. I got
swamped with other experimental problems (sigh) and the summary as well
as the sensors were and are overlooked! My sincere thanks to Adrienne,
Andrea, Brian, Carl, Debbie, Gerd, Jerry, Lawrence, Matthias, Michael,
Patrick, Paul, Phil, Rainer, three Roberts, Roy, Stephen, Steven, Tara,
and William.
First, I give my original question, then a very short summary, and then
attach the edited answers. They are all very instructive on their
solution to a problem common to all of us.
Happy resonating
Ulli
************************************************************************
First my original question:
Dear Colleagues,
May I ask for your advice on Oxygen sensors:
In our NMR room we have two oxygen sensors at different heights, as
recommended by the vendors. We already had one sensor fail twice each
time after only one year. Now the company tells us that we have to
expect to exchange these sensors every 1.5 - 2 years (cost about $200,
in addition to the calibration costs). I have not heard of such a short
life span before. Therefore my questions to you, who have oxygen
sensors, are:
- How long do your sensors work before they fail?
- Which brand do you use (thank you in advance for digging this
information out for me, if you can).
- Is it powered by a battery or from the main power supply?
- Who supervises it, you or the facility management?
**********************************************************************
- In summary, everybody mirrors the same experience that these sensors
are quite short lived.
- About everybody seems to have a different brand, so please see the
attached answers.
- The management seems to be mostly done by you, even though some
answers also refer to Safety / Facility Management personnel.
**********************************************************************
Because the answers are quite detailed and instructive on how you use
these sensors, I attach them, just edited a little bit to take out names
and some personal notes. (I hope I meet the right cut off.).
________________________________________________________________________
I can confirm this: we used 3 (handheld) sensors of "GREISINGER
electronic GmbH, D-93128 Regenstauf", which died after 1 year.
Replacement costs are 50 each sensor.
By the way:
ask some WWW sources about healthy risc of O2 lack. There are different
numbers to be found. www.bgchemie.de tells us, that a seroius risk is
present at O2 concentration lower than 10 %. Mountain climbers reports
that is no risk up to 4.000m height (which corresponds to a partial
pressure of 13% O2).
Is it a real safety risk in your lab? Isn't it easer to exhaust N2-gas
out of the room (He should, because of possible vacuum loss over long
time). Isn't it sufficient to maintain only 1 sensor (at 1.5 m height),
if you afraid?
Of cause: this is only valid for normal operation, not for long time
filling (i.e. during magnet installation processes).
________________________________________________________________________
I've recently discovered the same thing. I have five MSA oxygen sensors.
They were installed about 18 months ago in a new building that we had
built for a shielded 800. They started acting flaky a few months ago
(they frequently set off the alarm and turn on the overhead venting
system). I called the company and they told me that they only last for
12 to 18 months. The oxygen sensors are hardwired into the building
power, not on batteries, and I supervise them myself.
________________________________________________________________________
I'd be interested in your responses, as I have a failed sensor. It is an
Air Aware sensor, bought from MR Resources. I'm not sure how old it is,
probably 2-3 years. A colleague bought a similar sensor about 2 years
ago which failed after a few months, but it is still working OK after
being repaired/recalibrated.
________________________________________________________________________
...
We have a Vulcain VA-201M monitor which, after about a year, started to
go off sporadically. The company told me the sensor needs to be replaced
once a year (I forget how much it cost- I haven't got around to getting
facilities to take a look at it yet).
________________________________________________________________________
We have a Teledyne 335, at least 10 years old. It has replaceable fuels
cell sensors ($75) which last about 8 months after opening. It requires
weekly calibration with room air; we do this ourselves. If we forget to
calibrate it, it will drift downward and go into alarm within 2 weeks.
Although it plugs into the wall, it's basically a battery-powered device
with a continuous AC charger. We had to modify it ourselves to add an
on/off switch and an alarm-silence switch.
Due to the calibration and other issues, I probably wouldn't buy this
model again.
________________________________________________________________________
Please see below:
Therefore my questions to you, who have oxygen sensors, are:
- How long do your sensors work before they fail?
We change our sensors a minimum of once a year whether they need
it or not. It is just part of our yearly NMR maintenance routine.
- Which brand do you use (thank you in advance for digging this
information out for me, if you can).
We have a Biosystems ZoneGuard and use the Biosystems O2 filters.
- Is it powered by a battery or from the main power supply?
It is powered from the main power supply. I had it hooked to a battery
back-up but found that was unreliable.
- Who supervises it, you or the facility management?
I supervise it.
...
________________________________________________________________________
We use two "MSA Toxgard II" Monitors. They ran for about two years
before failure. I have not replaced them (yet). I have replaced the
little in-line air filters several times each, which extended the
lifetime. They are powered by the main power supply, and monitored by
me (the NMR lab manager)
_______________________________________________________________________
You have discovered one of the major nuisances of oxygen sensors. Our
building engineers installed units from MSA (Mine Safety Appliances
Company) in our labs. Each controller is hardwired for power (no
batteries) and is connected to a central monitoring point on campus.
The sensors do not seem to last much longer than 1 year. After a year
they start to decline and ultimately fail. Consequently, our facilities
people calibrate them every 6 months and replace them on a yearly basis
(i.e. one calibration between replacement).
________________________________________________________________________
We have relied upon a Crowcon II oxygen level sensor for several years.
The unit is a hand held model with a loud audible warning sound and a
bright visual warning flasher. The set points are user programmable
with respect to when to activate an alarm. Unit cost ca. $450 and has a
sensor that MUST be replaced once each year at a cost of ca. $80.
I often work alone in the lab and would highly recommend this device as
a necessity in all NMR labs.
________________________________________________________________________
We had an Oxigard II sensor which had just failed after about 1.5 years.
Same experience with the manufacturer, that is they said that was a
normal life span and we needed to buy a new sensor. At the moment I am
dealing with the facilities people to have them pay for it.
________________________________________________________________________
Our local engineer recommended oxygen sensors a few years ago. We
looked into the subject and decided not to use them. They are
contaminated by organic vapors and have a short life span in most
laboratory environments. Both of our magnets are located in small rooms.
During a nitrogen fill we have been able to make an oxygen sensor
respond when it is placed on the floor directly below the magnet. We do
open the lab doors when performing nitrogen fills and that eliminates
the problem. The need for sensors is only important when handling large
quantities of liquid Nitrogen such as prior to energizing an imaging magnet.
If you make the decision to go ahead with sensors, then I would go in
the direction of wall units with outside audio warning and a hardwire
relay to campus security. Then I would insist on maintenance by physical
plant to monitor performance and change the units and keep records.
Otherwise you are personally liable in the event of an accident.
...
_______________________________________________________________________
...
Wir haben diese Sauerstoffsensoren im Einsatz und ich bin mit den
Dingern hoechst unzufrieden. Zum einen handelt es sich generell um
Fluessig- bzw. Gelelektroden, deren Lebensdauer tatsaechlich
beschraenkt ist. Innerhalb welchen Zeitraums die ausgetauscht werden
muessen, weiss ich noch nicht einmal, auf alle Faelle muessen die
halbjaehrlich neu kalibriert werden. Das reicht aber trotzdem nicht,
weshalb gern schon deutlich frueher ein Sensor viel zu wenig Sauerstoff
meldet. Dann geht bei uns eine Rundumleuchte vor dem betreffenden
Gebaeude an. Im guenstigsten Fall passiert das am Wochenende und der
erschrockene Hauswachdienst hat dann gegen 2:00 Uhr in der
Fruehe meine Telefonnummer ermittelt und verschafft mir die ohnehin
heiss gewuenschte Unterbrechung meines Schlafes. Im Nomalfall geht die
Leuchte aber an, und niemand, nicht einmal die im Gebaeude arbeitenden
Mitarbeiter kuemmert sich auch nur eine Bohne drum. Voellig witzlos:
eine Alarmeinrichtung, die niemand ernst nimmt..
Noch schlimmer ist, dass sich ein Sensor in der Naehe eines Magneten
befindet und sich der Wartungstechniker (der natuerlich immer dann
kommt, wenn ich mich nicht drum kuemmern kann) einen feuchten Dreck um
die Befindlichkeiten irgendwelcher laecherliche 7 tage laufenden
Messungen kuemmert.
Im Gegenzug werden im betroffenen Gebaeude Teil pro Stunde 5000 m**3
(Kanada kennt doch metrische Daten, oder?) Luft gewechselt, davon sind
20% Frischluft. Wir muessen also schon beide im Raum stehenden Magneten
umschmeissen, um in Sauerstoffnoete zu kommen.
Nichtsdestoweniger hat es natuerlich bereits toedliche Unfaelle durch
Sauerstoffmangel gegeben, vorzugsweise freilich beim Stickstofffuellen.
Bei den Szenarien befand sich die betroffene Person aus irgendwelchen
Gruenden (z.B. ein Sturz) mit dem Gesicht am Boden, waehrend die
Sensoren (zumindest bei uns) in etwa 1,50 Meter Hoehe angebracht sind.
Egal, ob di am Boden liegende oder kriechende Person dort nun etwas
sucht, oder meinethalben durch den Sturz nicht handlungsfaehig ist,
waehrend der Stickstoff ueberlaeuft, wuerde der Sensor viiiiiel zu spaet
anschlagen (selbst, wenn ihn jemand ernst naehme).
Langer ironischer Rede kurzer Sinn: ich halte die Sauerstoffsensoren
fuer Schwachfug.
________________________________________________________________________
We use a single Emproco sensor as recommended by our safety regulations.
The sensor specified to last one year and sometimes lasts longer. It
costs about $250 to replace each time. Our sensor is on the mains power
supply. I, as laboratory manager, take care of it.
________________________________________________________________________
Our O2 sensors are from Wessington Cryogenics (UK). They need a
battery change and calibration every 18 months or so. Wessington come
and do the maintenance regularly for the units on our site. We also use
portable O2 sensors on the lN2 dewars and these are cheap from RS
Components (i.e., disposable).
From what I've seen when we looked into this, a 2 year maintenance
schedule is quite common. There's nothing fancy about calibrating, esp.
in the beautiful NS air!
________________________________________________________________________
we have three oxygen sensors installed in our 1995
NMR annex building (all at same height ...)
> - How long do your sensors work before they fail?
well, they're still "working" after 10 yrs. - however, after ca. 1-2
yrs. we got false alarms from one of the sensors, so it was
re-calibrated by some specialist (on place in the NMR building). The
same happened ca. 1 yr. later, and we were told that this is normal,
since the oxygen-selective membranes (?) in the sensor are aging. next
time I opened the control box and turned the offset up/down myself. Last
time I did this was > 2yrs. from now. Did they stop aging? Did they stop
working at all??? There are things you don't know and don't WANT to
know. Obviously the safety people forgot about the sensors long ago, and
since the NMR building is quite large, with a very efficient A/C with
very rapid air exchange
.
> - Is it powered by a battery or from the main power supply?
mains
> - Who supervises it, you or the facility management?
I guess facility management SHOULD do it ... (and pay for
the regular maintenance!)
________________________________________________________________________
We use personal detectors for those doing fills, but do not have
permanent sensors in the labs. The model is RKI Instruments OX-01. The
sensors need replaced every 2 years and are self-calibrating.
________________________________________________________________________
...
wir haben vor ziemlich genau zwei Jahren zwei tragbare O2-Gaspruefgerδte
(Micro III G202 mit Sensor MK376-5) der Firma GfG Gesellschaft fόr
Geraetebau mbh (
http://www.gfg-inc.com/deutsch/start.html) angeschafft.
Zum Betrieb wird eine normale AA-1.5V-Batterie verwendet. Die Geraete
sind sehr handlich und zuverlaessig, aber wir haben das gleiche Problem
wie Sie mit den O2-Sensoren. Der erste ist nach anderthalb Jahren
ausgestiegen, der zweite laeuft noch. In der Betriebsanleitung ist, wie
ich dann festgestellt habe, auch eine "Erwartete Lebensdauer" fuer
diesen Sensor angegeben, und zwar "2 Jahre in Luft". Der Austauschsensor
hat rund 220 Euro netto gekostet, einsetzen und kalibrieren kann man ihn
bei diesem Geraet allerdings selbst.
...
________________________________________________________________________
We don't use them and they aren't generally necessary in most labs
designed with higher air exchange. Anyway O2 sensors can last as little
as 6 months.
...
________________________________________________________________________
Beware, most oxygen monitors use "electrochmical" sensors. They may not
give you an accurate measurement of the Oxygen concentration in the
presence of Helium. The results can be fatal!
See
http://www.enmet.com/specs/HeliumOxygenMonitoring.pdf.
Yes, the sensors are short lived.
________________________________________________________________________
I have an oxygen sensor in the NMR lab as required by our safety
department. It is on the wall at the level of the head of the user. It
really does have a life-span of about a year and really does cost about
$200 to change the sensor (I calibrate it myself). I have another one in
our preparation lab (required because of insufficient ventilation) -
same story... I have no solution to offer.
They are imported from Oldham and something called Emproco - I haven't
found anything better so far.
I (facility manager) manage them, but when they fail they raise such a
racket that no-one in the vicinity will miss it.
We did have an accident in the cryogenics facility years ago, when
someone walked into the complex after some leak and passed out for lack
of oxygen (he is still with us today) - so I do take the sensor
seriously. I also lecture students on symptoms of oxygen deficiency as
part of the regular NMR lab safety protocol.
________________________________________________________________________
this is no total answer to your question, but it may be interesting for
you:
These oxygen sensors are constructed like an atmospherically open
electochemical cell
so they are a wearing part. One reaction partner is oxygen and the
voltage of the cell is proportional to the oxygen concentration in the
air. The life time of such a sensor indeed seems to be 1-2 years.
________________________________________________________________________
Dr. Ulrike Werner-Zwanziger
Adjunct Professor
Senior NMR Spectroscopist
Department of Chemistry, IRM, ARMRC
Dalhousie University
Halifax, NS, Canada, B3H 4J3
Phone: (902) 494 8085
FAX: (902) 494-1310
e-mail: Ulli.Zwanziger_at_Dal.ca
Received on Sat Feb 18 2006 - 11:53:28 MST