Re: [OT]: How much air does 6.4kg of R-22 displace in a 40m3 container at 20degC

Hi Sean,

Thanks for the course correction. I read "slightly disagree" as a polite
way to say "strongly disagree" and took heed. :).

I showed your response to a colleague (who enjoyed reading your post) and
agreed that we wish you were on our team or better yet, their team. and
thankful for pointing out the flaws in my logic.

We have surrendered as it is not possible to provide an irrefutable
opposing argument.   We (many) still consider the additional controls to
have introduced way more risk than it has reduced.   The irony.

Once again,  I (we) very much appreciate your time and input.

Justin

On Thu, Jan 2, 2025 at 11:09 AM Sean Breheny <[email protected]> wrote:

> I'm glad to help in whatever little way I can. However, I do have to
> slightly disagree with you about the appropriateness of using an oxygen
> meter to detect another gas by a process of elimination. The problem is
> that oxygen meters can be off by some fraction of a percent (let's say
> 0.2%) and that is fine when it comes to oxygen itself, but since oxygen is
> only 20% of air normally, the reduction in oxygen needs to be multiplied by
> 5 to get the concentration of whatever "other gas" is present, meaning that
> you will have 1% error in your estimate of the amount of R22 (or other
> contaminant). The maximum permitted short term exposure level for R22 is
> 1250ppm or 0.125% - so using an oxygen meter like you suggest could allow
> up to 8x the max allowed level of R22 without showing any change in oxygen.
>
> I think you probably do have enough safety given the amount of ventilation
> but I think you need to focus on proving that and not try to misuse an
> oxygen measurement to infer R22 concentration.
>
> Regarding stratification (R22 settling toward the floor because it is
> denser than air) - both the ventilation flow and also just diffusion
> (movement of gas molecules) work against that. Gravity, obviously, works in
> the opposite direction and tends to make the denser gas collect near the
> floor. The end result is a gradient of concentration, with a bit more R22
> near the floor and a bit less toward the ceiling. I don't know an easy way
> to estimate how much that will happen (the rigorous way would be
> computational fluid dynamics simulation along with measurements but that is
> overkill).
>
> Sean
>
>
> On Wed, Jan 1, 2025 at 4:05 AM Justin Richards <[email protected]>
> wrote:
>
> > Hi Sean,
> >
> > thank you.
> >
> > Thank you so much for doing the hard work for me.  Would have been very
> > happy with some pointers as I was struggling to make sense of my internet
> > searches and I am ecstatic with the effort you have gone to.  Very much
> > appreciated.  I hope to use your approach to support our case.  More
> > Details below if interested (it is a bit of a rant. I need to vent).
> >
> > Regards Justin
> >
> > I erred on the side of caution so the figures I originally stated are
> worst
> > case, over estimating the amount of R22 and underestimating the volume,
> and
> > left out details about forced positive ventilation, recirculation and
> > greater than a 1m2 opening directly to open fresh air at the top
> > when accessing the container.
> >
> > We have been in a to and fro battle with the OH&S folk who are demanding
> of
> > us to do what we consider to be extreme additional measures including
> > lugging around bulky exhaust fans with cumbersome ducting to provide
> > positive ventilation to a container that is always being positively
> > ventilated.by way of the aircons and their design. They demand this
> > regardless of gas detector readings.  I have measured the fresh air
> intake
> > but dont have the numbers to hand. I was satisfied the turn over is high.
> >
> > They have added so many additional safety measures that we believe the
> task
> > is no longer safe, with ropes, heavy winches and poles and ducting and so
> > much gear we are tripping over and can not fit into the vehicles safely,
> > with so many steps in the overly complicated verbose procedure.
> >
> > Our basic argument is that it is safe if the Gas detector reads 20.9%
> > oxygen and the other 3 detectors read zero for CO H2S and  combustibles.
> > This view is shared by all the people who regularly have to enter but not
> > by those 1000's of miles away.
> >
> > Their (OH&S) response is that the meters can not detect R22.  We agree,
> but
> > counter by stating it will show less than 20.9% if there is R22 in levels
> > that are hazardous.  They refuse to accept this.restating that they do
> not
> > detect R22, and we restate they will detect the reduction in oxygen
> levels
> > implying that there is something else in the space.
> >
> > They also argue that R22 is denser than air and will settle out and
> create
> > a dangerous zone.  We agree that it is denser but we can not agree that
> it
> > will settle out as It would require a particular set of conditions that
> > simply can not be met at 20DegC with a > 1m2 opening and running air
> > conditioners pushing in fresh air and circulating.(I hope I am right
> about
> > it not settling out)
> >
> > Oddly, they updated the procedure stating that it is fine to enter with
> > levels between 19.5 to 23.5% O2, and some figures > 0 for the other
> sensors
> > and dismiss our suggestion that history (where all good lessons are
> > learnt)  has taught us that something is up and needs to be investigated
> if
> > it is not bang on 20.9% or the other readings are not 0.
> >
> > For the record, the bump tested, regularly calibrated, regularly replaced
> > meters have always read 20.9% in the last 20+ years except a few
> instances
> > where we got another meter and sent it for repair and cal or replacement.
> >
> >
> > On Wed, Jan 1, 2025 at 8:22 AM Sean Breheny <[email protected]>
> > wrote:
> >
> > > HI Justin,
> > >
> > > The best way to approach this is via the ideal gas law: PV=nRT. One set
> > of
> > > consistent units for that are P in kPa, V in liters, n in moles,
> > R=8.314, T
> > > in Kelvin.
> > >
> > > R-22 has a molar mass of 86.47 grams. 6.4kg is therefore 74 moles.
> > > Assuming 300 kelvin, 100kPa pressure, and a volume of 40000 liters
> > (40m^3),
> > > there are 1604 moles of gas in your room, regardless of composition.
> > > Before adding the R-22, you have roughly 20% oxygen (321 moles) and 80%
> > > nitrogen (1283 moles).
> > > Adding 74 moles will briefly increase the pressure but very quickly it
> > will
> > > equilibrate with the outside via the vents and you will end up with the
> > > following proportions:
> > > oxygen: 321/(1604+74)=19.1%
> > > nitrogen: 1283/(1604+74)=76.5%
> > > R-22: 74/(1604+74)=4.4%
> > >
> > > The reason this works is that doesn't matter much whether the gasses
> mix
> > > thoroughly before any escapes out the vents or if the 74 moles of R-22
> > > pushes out 74 moles of air and THEN mixes, since 74 is such a small
> part
> > of
> > > 1604, the error in the estimate is only around 4% of each value at
> worst.
> > >
> > > (I see now that you did specify the temperature as 20C which is 293
> > kelvin
> > > and not 300, but the numbers are close enough).
> > >
> > > This would leave you with adequate oxygen (the minimum is about 18%
> > before
> > > you significantly affect people). However, the 4.4% R-22 is well above
> > the
> > > 1250ppm (0.125%) short term weighted average limit per NIOSH. R-22 is
> > > pretty non-toxic but it has a much greater narcotic potential than air,
> > so
> > > 4.4% might be enough to make someone drowsy or affect judgement. The
> > vents
> > > would allow gas exchange to the outside and eventually the air inside
> > will
> > > return to being relatively R-22 free, but calculating how long that
> will
> > > take with passive ventilation is difficult.
> > >
> > >
> > > Sean
> > >
> > >
> > >
> > >
> > >
> > > On Mon, Dec 30, 2024 at 7:07 PM Justin Richards <
> > [email protected]
> > > >
> > > wrote:
> > >
> > > > End Game Question:-
> > > >
> > > > Will it be safe and within safety limits if 6.4kg of R22 is released
> in
> > > > 40m3 container that has vents at the top of the container?.
> > > >
> > > > From random web page
> > > >       1 Kg of air has a volume of ~0.816 m³ (density ∼ 1.225 Kg/m³)
> > > >
> > > > From https://www.engineeringtoolbox.com/r22-properties-d_365.html
> > > >
> > > >       R22 at 20degC has vapour volume of 0.02593 m3/kg
> > > >
> > > >        Therefore density is inverse of above 34kg/m3 <- seems too
> > high, I
> > > > think I am wrong.
> > > >
> > > >      Therefore 6.4kg so at 20DegC expands to ( 0.02593  x 6.4)  =
> > > *0.166m3*
> > > > <- seem to low, I am definitely wrong
> > > >
> > > > Assuming  calcs are wrong  so looking elsewhere.
> > > >
> > > > From
> https://www.agas.com/media/uk2o4u1w/r22-technical-information.pdf
> > > >
> > > >     R22 Vapor Density (bp,lb./ft^ 3)  0.294 (Temperature is not
> stated)
> > > >    Converting to bp,lb/m3 (35 ft3 in 1m3)  10.29
> > > >    Converting to kg/m3      4.6
> > > >
> > > > If 4.6kg/m3 (still seems high) is correct then 6.2kg will displace
> > > *1.3m3*
> > > > ,- seem too low
> > > >
> > > > Both results above (0.166m3/6.4kg and 1.3m3/6.4kg) look wrong so
> hoping
> > > the
> > > > list may be able to point me in the right direction.
> > > >
> > > > Regards Justin
> > > > --
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