Autoclaving the mail

[Tim May]

On Wednesday, October 17, 2001, at 11:15 AM, Trei, Peter wrote:

>> Harmon Seaver[SMTP:hseaver at cybershamanix.com] wrote:
>>
>>
>>         I'm not understanding the comments about wetness affecting mail
>> in a pressure cooker -- using it as an autoclave, that is. I would
>> assume anyone doing this would put the perishable objects in a
>> waterproof container, such as a canning jar. You can get them in 1/2
>> gallon size. And I'm sure there are any number of steel, aluminum, etc.
>> waterproof containers that would work as well.
>>
>> Harmon Seaver, MLIS
>>
> The whole point of an autoclave is that the superheated steam and
> condesing superheated water drops transfer heat to the target faster
> than simple hot air at 1 atm.

I disagree. While autoclaves and pressure cookers/canners do indeed 
"heat faster," the main purpose is not speeding up the heating.

Rather, it is in getting the temperature to 240 F or higher, the 
temperature required to kill organisms which are not killed at mere 
boiling water temperatures. And, secondarily, in getting the temperature 
in all the various nooks and crannies of instruments. (In this part, I 
agree that "heating faster" is important...but it's only a secondary 
issue, and of no practical importance for the "autoclaving the mail" 
proposal: one just leaves the mail in the autoclave or pressure canner 
for another couple of minutes, thus compensating for any slight lag time 
in heating.)

In a pressure canner, this 240 F temp is needed to prevent botulism in 
low-acid foods (meats, some vegetables). High-acid foods like jams and 
jellies and fruits can be canned in ordinary boiling water.
>

> Putting the material to be sterilized in a waterproof container defeats
> this goal. Putting it in a pressure tight container such as a canning
> jar is doubley futile - either the superheated steam and water won't
> get to the material to be sterilized, or the container will fail
> catastrophically.

Not that I am endorsing this idea, but the contents of a sealed 
container will _still_ see the internal 240 F temperature (albeit with 
some small thermal lag, depending on construction, thermal mass, etc.). 
Papers inside a sealed metal foil package, for example, without 
insulation in the foil, will reach the ambient temperature (240 F) 
pretty quickly.

It is not necessary for the steam to touch the material being sterilized.


--Tim May
"Gun Control: The theory that a woman found dead in an alley, raped and
strangled with her panty hose,  is somehow morally superior to a woman 
explaining to police how her attacker got that fatal bullet wound"