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Previous by Date: Subject: Re: [DCHAS-L] Laboratory Gas Detection Date: Tuesday, March 12, 2019 at 2:21:24 PM Author: Monona Rossol <0000030664c37427-dmarc-request**At_Symbol_Here**LISTS.PRINCETON.EDU> |
Next by Date: Subject: Re: [DCHAS-L] Laboratory Gas Detection Date: Tue, 12 Mar 2019 20:16:11 +0000 Author: Monona Rossol |
What if the cylinders are in a room with hoods that run constantly?
Just asking how this would impact a leak. If the tanks are next to the
hood does this remediate the situation itself?
Thanks in advance!
-Eric Goff
On 3/13/19, Monona Rossol -Eric Eric W. Goff ---
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<0000030664c37427-dmarc-request**At_Symbol_Here**lists.princeton.edu> wrote:
> Best advice is:
>
> The sensor should be placed near the most probablelocation for a gas leak.
> 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.
> 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.å Once they reach room temperature, they will
> all will disperse in all directions.
> So placement is more dependent on 2) the temperature of the gas release with
> respect to the temperature of the air in the roomå and 2) the size of the
> expected release.å 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.
> å 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?
> å And where are those very heavy chlorofluoro hydrocarbon propellant gases
> today?å å Once you have theå 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
> To: DCHAS-L
> 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.å å å å å Oxygen sensors/detectors with low and high-level alarmswill be
> located in areas that present a potential asphyxiation hazard due tothe
> presence of manifolded or central liquid nitrogen or other
> asphyxiantgases.2.å å å å å Before any large volume container of compressed gas
> orcryogenic liquid is used, Environmental Health andSafety must be consulted
> to determine the need for oxygen detectors and oxygendepletion alarms.
> Environmental Health and Safety will perform the worst-casescenario
> calculation assuming the entire volume of container contents arereleased.
> If the final oxygenconcentration is lower than 18%, oxygen sensors and
> alarms should be placed. Thecalculation to be used is:å Final O2
> concentration = 20.9 ‰?? 20.9*(Vgas/Vroom)whereVgas = 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 |
>
> å 3.å å å å å Oxygen depletion alarms should not only sound locally. Allalarms
> should be tied into the Facilities Operations building alarm system.
> 4.å å å å å The placement of the sensors should also be determinedby EH&S,
> depending on the nature of the gas.
> | 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) |
>
> The sensor should be placed near the most probablelocation for a gas leak.
> Whenever possible, the read-out panel or a strobeshould be placed in a safe
> area outside the room. The alarm must be audibleboth by the location of the
> read-out panel and by the sensor.
>
> On Tue, Mar 12, 2019 at 9:49 AM Stephen Beaton
>
> Hi all,å I am researching best practice for fixed gas detection in
> laboratories in the university setting.å 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?å Thanks in
> advanceSteveå Stephen Beaton, MSc, CHO, CRSP
> Chemical Safety Manager
>
> Environmental Health and Safety Office
> 902.494.1934å |å steve.beaton**At_Symbol_Here**dal.ca
> DALHOUSIE UNIVERSITYå å ---For more information about the DCHAS-L e-mail list,
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> ---
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--
Best Regards,
Chemistry Educator
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