High altitude autoclaving - (Feb/17/2010 )
I have been having trouble with sterilizing media with a typical autoclave (15psi) for 30 minutes and I now think it's the altitude. I am in Albuquerque - 5300 feet - and obviously this lowers the boiling point but from what I have been reading this also reduces the pressure, which should be held at 15psi, down to approximately 10-11psi.
My question is whether longer durations at lower pressures (10-11 psi) will equate or do I just need to get an new autoclave which will support increased pressure? Thanks in advance!
inside your autoclave the pressure gets adjusted because it is a closed system (autoclave closed, water boils, steam does not get out, pressure is increasing until the right pressure is reached, then the time starts counting). I do not think the altidude has an influence on the success of autoclaving.
But: you have your medium in (loosley) closed bottles? This could influence the sucess of your attempt, as the steam has to get to the medium to sterilise it.
Alternative: you have your bottles not closed enough so there are bacteria getting in from the air when cooling the media before use
Or you have a contamination in your laminar flow.......
Increasing the time is only useful when autoclaving huge amounts (like three four liters in one bottle) as there is more time needed to heat and saturate your medium with hot steam. Otherwise longer times can burn your medium so it will not work as you expect it.....so be careful with longer times and higher pressure.
If there's a hospital in your area, maybe you could make a call to their sterilization department (it's usually called "central sterile supply" or some such) and talk to one of the people there -- they're usually quite expert in these matters.
I'm not so sure about that: In the beginning, when the water starts boiling and the steam has to replace the air, the autoclave is not a closed system but open. Therefore the higher altitude and less ambient pressure has some influence, as the water boils at lower temperature (the thermometer should show that).
Then you (or the automatic system) close the gauge and the pressure increases inside, here there might be some influence how the autoclave is regulated and what type of gauge is used: Most pressure gauges are designed to measure the amount of pressure above the ambient atmospheric pressure (and not absolute values), therefore the gauge might open too early to let steam off, because the system detects a too high pressure inside (as it compares the pressure inside to a too low ambient pressure outside). Then the temperature inside is always too low.
Actually I don't know if the altitude you are has that much influence on pressure and boiling temperatures, but there should be people how now that.
If it's really a problem you (or the service people) might can solve it in that way, that the gauge is calibrated for the lower ambient atmospheric pressure.
excellent explanations - thanks guys.