Hello everyone,
I received many responses to my question, and they are all very helpful.
As always, this community provides a wealth of knowledge to all things NMR.
Many thanks!
A PDF containing all the responses (with identifying information removed) is
attached if you'd like to read them fully. Here is the summary of responses:
1. High ceiling does not necessary offer enough protection from helium during
a quench as there is significant gas mixing. Oxygen can become depleted at floor
height underneath the helium cloud. Calculation should be done.
2. Some reported a quench did trigger their O2 sensor in the lab, while others
reported the quench did not trigger.
3. Bruker's site planning guide suggests having at least two O2 sensors in the
lab, one near the ceiling and another near the floor (reports vary between 18
inches off the ground to chest height). Of the two, several responses agreed the
one near the floor is the important one, and some labs have opted not to install
a sensor near the ceiling.
4. There is broad consensus that LN2 is less of an issue than helium, but there
are scenarios where large amount of nitrogen can flood the lab. Several responses
noted that maintenance LN2 fills are enough to trigger their O2 sensors. Other
possibilities include failure of LN2 tanks, and one response noted a specific
case where the quench happened from the outside-in (i.e., the LN2 was boiled off
before helium) due to improper LN2 fill.
5. Several responses have noted there is limited indication to observe increased
LN2 boil-off or nitrogen gas leaks, so the O2 sensors can offer early warning.
6. O2 sensors are required in many NMR labs, either by EH&S or building code,
especially in newer buildings.
7. Many responses noted frustration dealing with O2 sensors giving false alarms.
Portable O2 sensors can be used to double check for bad readings or as backup
monitors. Long life O2 sensors (10 years, e.g., PureAire) are favored.
Best,
TC
UCLA Chemistry
----- Original Message -----
> From: "AMMRL List" <ammrlrev_at_webserver2.chem.hawaii.edu>
> To: "ammrl" <ammrl_at_ammrl.org>
> Cc: ckolodziej_at_ehs.ucla.edu
> Sent: Thursday, April 28, 2022 4:28:41 PM
> Subject: O2 Sensor in the NMR Lab
>
> Hello AMMRL,
>
> We currently don't have O2 level sensors in our NMR lab. We've been discussing
> with our EH&S on whether to install them.
> At the moment, we think we'd be ok when there is a large amount of helium gas
> escaping (e.g., during a quench) because of the high ceiling in the lab, but
> we are more uncertain about nitrogen.
> What are some of the possible events that can cause a large amount of nitrogen
> gas to flood the NMR lab and potentially suffocate someone? (Being in southern
> California, we already covered earthquakes).
>
> I will provide a summary. Thank you so much!
>
> Best,
> TC
> UCLA Chemistry
>
Received on Mon May 02 2022 - 12:42:32 MST