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This is interesting as whenever we use an O2 cylinder in the field 
(treatment or teaching), we run the risk of depleting it - & we have on 
#ous occassions.  Never has the station filling it (usually Roberts O2) 
given any hassle refilling our cylinders.

Aside from the fact that medical O2 cylinders (rumour is all cylinders) 
being evacuated prior to refill, if U think of it, the question is what 
contaminatioon, to what extent?

The pressure in an empty the tank is 1 ATA (unless we assume that the 
tank, after being drained, ws kept open & was subjected to cooling or 
heating or was exposed to P > or < 1 ATA).  Thus any gas phase 
contaminants can enter only via diffusion, a relatively slow process.  
The next issue is the conc of said gas phase contaminants in the 
ambient environment.  Obviously not very high, as that would render the 
ambient environment hazardous.  

Thus it appears that that contaminant entry into a fully depleted (@ 1 
ata) tank of any type, maintained in a healthy environment becomes a 
non issue.


You wrote: 
>
>
>> From:          DOUG MATHIESON <mathieson@go*.ne*>
>> Subject:       TRANSFILLING OF EMPTY O2 CYLINDER
>
>> I am transfilling O2 tanks at work and occasionally we get a empty
>> cylinder come back for filling with the valve left open. We have a
>> suction unit in the transfilling system to remove any residual O2 
before
>> filling.They seem to feel that this suction will remove contaminants
>> from a  empty tank.
>> 
>> I have been refusing to fill any tank that comes back empty due to
>> possible contamination.
>> 
>> I would appreciate any collaboration I can get on this matter 
outlining
>> the sources of contamination and consequences involved. I am asking 
for
>> help in this matter because as of now i am just one lone voice and I
>> know you can explain the reasons more technically and eloquently 
than I
>
>    Doug,
>      While it is unlikely that there will be any contamination in 
>the tank, the possibility still exists, and the customer knows they 
>should leave some gas in the tank and the valve closed. So I have 
>a firm policy of visually inspecting every tank that comes into 
>the store empty with the valve open. With the exception of 
>doubles, the visual inspection only takes about 5 minutes, I do it 
>while they wait, and the charge for the visual inspection encourages 
>the customer not to do it again (it's kind of like a speeding ticket). 

>
>Ted
>
>
>Ted Green (Owner)
>Tidewater Aquatics (Dive Store)
>Salisbury Maryland USA
>Master Instructor SSI #178
>Trimix Instructor TDI #029
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