Is the effect of boiling at reduced pressure same as boiling at high pressure?

Physics Asked by Manu Soman on December 23, 2020

I guess that boiling itself would be the same in both cases, but what about its effects? For example, we boil water to disinfect it. So, would water boiling at low temperature at low pressure have the same effect? And what are the other possible differences?

One Answer

Good question. What actually matters, according to the CDC, is moist heat. High humidity and high temperatures together are very effective at sterilizing.

In lower pressures, water boils at a lower temperature. and thus:

If you want to sterilize the water and make it safe to drink, the CDC recommends boiling it for one minute at elevations under 6,500 feet and for three minutes at elevations over 6,500 feet.

The fact that you have to boil it longer at higher altitudes is a good indication that the lower pressure makes sterilization via boiling less effective.

Autoclaves, designed for sterilization of surgical equipment, operate hotter than boiling. 121C and 132C are common temperatures to sterilize faster and better. They typically use steam rather than water, for the obvious reason that water will have boiled already.

From the best I can discern, there is nothing magical about the act of "boiling" for sterilization. Its the heat and water that matter. However, boiling has a long history of being a very reliable temperature that can be achieved with great regularity without any scientific equipment. Once it starts bubbling, you can start your timer. Otherwise you would need to carefully monitor the temperatures during the process.

Answered by Cort Ammon on December 23, 2020

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