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Previous by Date: Subject: Re: [DCHAS-L] SO2 exposure Date: Tuesday, March 12, 2019 at 11:30:38 AM Author: Dan Blunk <000006969d6900fa-dmarc-request**At_Symbol_Here**LISTS.PRINCETON.EDU> |
Next by Date: Subject: Re: [DCHAS-L] Laboratory Gas Detection Date: Wed, 13 Mar 2019 02:48:49 +0800 Author: Eric Goff |
Best advice is:
The gas density and molecular weight are not very crucial for sensor placement, because all those gases, if released at room temperature will disperse in all directions about evenly unless is the release is so massive in volume that mixing with air is not occurring because the release is displacing room air in the vicinity of leak.
The sensor should be placed near the most probable
location for a gas leak.
Conversely, every one of those gases will head straight for the floor if they are under pressure and expand during release which makes them significantly cold and dense. Once they reach room temperature, they will all will disperse in all directions.
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So placement is more dependent on 2) the temperature of the gas release with respect to the temperature of the air in the room and 2) the size of the expected release. For slow, small leaks, placing the sensor close to the source is best because no matter what the gas is, it will quickly come to room temperature, mix with air, and begin the processes of dispersing evenly throughout the room without respect to the weight of the gas with respect to air.
May sound counter intuitive, but check it out. 'Tis so.
If you isolate a bottle of air for 10,000 years and don't disturb it, will the heavier molecules be more concentrated toward the bottom of the bottle? And where are those very heavy chlorofluoro hydrocarbon propellant gases today? Once you have the the answers to those questions and the technical reasons for the answers, all the rest falls into place.
Monona Rossol
-----Original Message-----
From: Mark Bachrach <markbachrach2015**At_Symbol_Here**U.NORTHWESTERN.EDU>
To: DCHAS-L <DCHAS-L**At_Symbol_Here**PRINCETON.EDU>
Sent: Tue, Mar 12, 2019 10:02 am
Subject: Re: [DCHAS-L] Laboratory Gas Detection
From our O2 alarm policy currently making its way through our policy committee:
1.
Oxygen sensors/detectors with low and high-level alarms
will be located in areas that present a potential asphyxiation hazard due to
the presence of manifolded or central liquid nitrogen or other asphyxiant
gases.
2.
Before any large volume container of compressed gas or
cryogenic liquid is used, Environmental Health and
Safety must be consulted to determine the need for oxygen detectors and oxygen
depletion alarms. Environmental Health and Safety will perform the worst-case
scenario calculation assuming the entire volume of container contents are
released. If the final oxygen
concentration is lower than 18%, oxygen sensors and alarms should be placed.. The
calculation to be used is:
Final O2 concentration = 20.9 - 20.9*(Vgas/Vroom)
where
Vgas = volume gas released in cubic meters
Vroom = room volume in cubic meters
Liquid
Gas
1L Liquid Nitrogen
0.694 m3 Nitrogen
Gas
1L Liquid Helium
0.757 m3 Helium Gas
1L Liquid Argon
0.847 m3 Argon Gas
3.
Oxygen depletion alarms should not only sound locally. All
alarms should be tied into the Facilities Operations building alarm system.
4.
The placement of the sensors should also be determined
by EH&S, depending on the nature of the gas.
The sensor should be placed near the most probable
location for a gas leak. Whenever possible, the read-out panel or a strobe
should be placed in a safe area outside the room. The alarm must be audible
both by the location of the read-out panel and by the sensor.
Gases
Gas Density
Sensor Placement
Argon, Heavy Hydrocarbons
Greater than air
Closer to the ground
Hydrogen, Helium, Methane
Less than air
Near the ceiling
Carbon Monoxide, Nitrogen
Similar to air
At or near breathing level (4
to 6 ft. from the floor)
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On Tue, Mar 12, 2019 at 9:49 AM Stephen Beaton <Steve.Beaton**At_Symbol_Here**dal.ca> wrote:
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Hi all,
I am researching best practice for fixed gas detection in laboratories in the university setting. There are certainly a number of variables to consider. Does anyone have guidelines/ standards/ decision-trees
to establish whether detectors for flammable, oxygen-depleting and toxic gases are required in the laboratory?
Thanks in advance
Steve
Stephen Beaton, MSc, CHO, CRSP
Chemical Safety Manager
Environmental Health and Safety Office
902.494.1934 | steve.beaton**At_Symbol_Here**dal.ca
DALHOUSIE UNIVERSITY
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