From: Alan Hall <ahalltoxic**At_Symbol_Here**MSN.COM>
Subject: Re: [DCHAS-L] Oxygen Sensor
Date: August 29, 2012 7:28:17 PM EDT
Reply-To: DCHAS-L <DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU>
Message-ID: <CACO1vYPKbkLAZoWcZSci0E=hK-=rOSdwhe_tAVO5eUCj7KiUWg**At_Symbol_Here**>

Aas a late favorite advocate for health and safety internationally used to address us,
Sure, Neil can tell more about SCBA vs. SCUBA that perhaps any of us.  I wish my old scar tissue in my ears would let me join him in his diving experineces.
But there's no place for SCUBA in a lab unless Jacques Cousteau comes back to life and gets one of his under the sea floor where at those depths you had to use heli-ox.
So let's get back on track.
Simple asphyxiants can injure or kill.  Well known facts.
N2 as liquid N2 can off gas in sufficient quantities even from relatively small containers to pose a  health- or life-threatening risk in certain enclosed-space conditions.
How does one approach this?
First, I think all the comments about where sensors and warning signals make a great deal of sense.  If you can prevent someone from going into hazardous conditions, then the response should be by those trained and equipped to do so.
Anyone here want to take the Advanced Hazardous Materials Life Support Course?  Disclaimer:  I an a verified provider and instructor and a member of the Scientific Advisory Committee, but I receive no remuneration unless I actually teach in a course and then we are admonished to mainly accept travel expenses and perhaps (but not necessary) a small honorarium.  Check it out at  We do discuss this amongst many other things.
Next, if you can PREVENT something, you don't have to RESPOND to it.  All those comments are good.
Third, who has current knowledge of the OSHA Regulations for entry into enclosed spaces with perhaps hypoxic atmospheres?  Might help some if those with current knowledge actually make a quote to the O2 concentrations and the exact reg not my field of expertise, just know they exist.  Great to have a 4-gas meter better to know what the results mean!
Alan H. Hall, M.D.


Date: Wed, 29 Aug 2012 16:03:41 -0400
From: bjwiehe**At_Symbol_Here**OWU.EDU
Subject: Re: [DCHAS-L] Oxygen Sensor

I am absolutely flame red with embarrassment!!  I even looked it up so I would not make that mistake.  I pull the red flag in the first week of our semester..

On Wed, Aug 29, 2012 at 2:50 PM, Jean & Ken Smith < smith.j.k**At_Symbol_Here**> wrote:

Hi Barb,

First =96 the term is SCBA not SCUBA.  The SCUBA is for underwater use.  When working for Cal/OSHA I encountered a person trying to don the SCBA as an SCUBA.  Fortunately, he was inside a filtered operations room.  This was in a huge gaseous phenol release so he didn't get hurt.  He obviously was not trained in the proper use of the SCBA and the company was hit with a serious citation for it.


The SCBA is mandatory to enter an oxygen deficient room unless a handheld gas monitor is used to verify that actual oxygen concentration is not hazardous.  Pay attention to the local state OHSA regulations on oxygen deficient atmospheres so you don't get into trouble.  They are actually good common sense regulations to prevent deaths. 


The oxygen room monitor needs to be installed according to regulations with the readout on the outside of the room or building.  The sensor must be recalibrated often due to the deterioration of the sensor.  It will need to be re-spanned at least each 6 months to assure a good response to low levels of oxygen.


At the lab where I was the EHS officer, we had a large liquid nitrogen leak in a room full of dewars containing biological specimens.  The alarm went off and we double checked the atmosphere by slightly opening the door and putting the handheld monitor inside.  The readings were very low % and would have been deadly if entered.    Especially dangerous is a liquid nitrogen spill/leak due to its density which will pool on the floor and easily rise to the nose level with asphyxiating consequences.


Training for the SCBA is regulated by OSHA and needs to be followed closely.  If no person has accreditation for training on SCBAs, then a professional trainer will be necessary.


End result:  Be very careful when dealing with asphyxiating gasses for they can and will bite you.


Ken Smith (former CIH, now retired)


-----Original Message-----
From: DCHAS-L Discussion List [mailto:dchas-l**At_Symbol_Here**MED.CORNELL.EDU] On Behalf Of Barbara Wiehe
Sent: Wednesday, August 29, 2012 10:23 AM
Subject: Re: [DCHAS-L] Oxygen Sensor


Thank you for your responses.

Neal, fair enough put the red flags away...I was thinking scuba but it isn't going to fly with anyone here to go to that extent.

I appreciate getting feedback from your perspectives rather than push back from others.


On Wed, Aug 29, 2012 at 12:45 PM, Neal Langerman < neal**At_Symbol_Here**> wrote:

Several thing =96 first and foremost The only protection for an oxygen deficient environment is a supplied air source.  Thus, a question regarding "respirator fit" raises a flag.


Having supervised the installation of many oxygen sensors in locations where a deficiency can occur, here are some thoughts


The sensor should be located IN the area to monitor and installed according to the manufacturer's instructions.  Pay particular attention to the vertical height instruction.


The sensor is low voltage, but the installation still must comply with the NEC.


The alarm should be in the monitored area and repeated just outside the affected zone and also at a central monitoring location.


Provide regular maintenance as required by the manufacturer.  While using a two gas calibration to set the span works, some sensors are calibrated with ambient oxygen, set to 20.8%.  It is very useful to periodically test the sensor with a low oxygen source. 


Most electrochemical oxygen sensors require replacement every two years.  In the very dry climate of southern California, we find that they need more frequent replacement.


False alarms from an oxygen sensor should be very infrequent.  If false alarms occur with an annoying frequency, work with the manufacturer to fix it =96 false alarms lead to the "chicken little" problem.


Your responders to an alarm, be it maintenance or other, should bring a working 4-gas portable with them to provide a back-up to the installed system.


Finally, installed sensors are really great, but they require active PM and some understanding of their limitations.




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From: DCHAS-L Discussion List [mailto:dchas-l**At_Symbol_Here**MED.CORNELL.EDU] On Behalf Of bjwiehe**At_Symbol_Here**OWU.EDU
Sent: Wednesday, August 29, 2012 7:01 AM
Subject: [DCHAS-L] Oxygen Sensor


We are installing an Oxygen Sensor in a room using Liquid Nitrogen.   Question, why do you mount it in the room where loss of Oxygen would be present?   What type of training should the technician have overseeing the monitor?(ie respirator fit)



Barb Wiehe



Barbara Wiehe

Ohio Wesleyan University
Environmental Health and Safety / Greenhouse Manager


Barbara Wiehe

Ohio Wesleyan University
Environmental Health and Safety / Greenhouse Manager

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