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

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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