On Wednesday, October 17, 2001, at 11:15 AM, Trei, Peter wrote:
Harmon Seaver[SMTP:hseaver@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"