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

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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