Agree with everything written regarding carbon filters. I operated ours in a clean room environment so atmospheric contamination would have been far better controlled, leading to better operational life cycles. I never took that into account.
I would also say that it’s your lungs, you protect them as you see fit. I’ve just typed this up as it may be of interest to some.
Those particulate filter change times are simply outrageous. To me that means one of two things. Either the filters are not correctly sized so they are quickly overloaded, or (cynical view) the company has decided that overselling consumables is a way to supplement income.
A HEPA filter is not a sieve (common misconception), it is a maze. I attended several (five I think) courses run by Pall filtration in the course of my Pharmaceutical production career, and they used very good graphics illustrating this concept.
To summarise, the depth of filtration material to be crossed is what makes a particulate filter effective. The particles drawn in by the air have to navigate labyrinthine pathways as the air crosses the matrix, and eventually, due to the many changes of direction they are subject to, become impacted on the filter wall and are removed from the airstream. As more particles are impacted, the “maze” becomes more involved, so removing particles more effectively.
There are three ways you can get particulate breakthrough in this type of application. The first is mechanical failure of the filter matrix. The second is by the contaminant challenge at one time being too great for the filtration matrix’s ability to remove particulates, and the third is that the challenge partials are too fine for the filter to remove them all so they are carried through on the airstream. The first is eliminated by use of quality components. The others are eliminated by utilising a HEPA filter that has been appropriately sized for the task in hand.
With use a HEPA filter becomes more effective at its primary task, removing particulates. However, as it becomes more efficient at removing particulates, the airflow velocity drops off until it is lower than an effective threshold so rendering the filtration device ineffective. This is when the filter needs to be replaced.
Here’s some background.……My reasons for attending these filtration courses was to enable me to fully understand the concepts involved in worker protection and the design, installation, testing, and maintenance of bio containment equipment. This equipment included protected powder discharge systems and biological laminar flow safety cabinets.
These systems were velocity airflow tested daily, and smoke tested (particulate challenge) at three monthly intervals. No HEPA in my experience had a life of less than two years, and most of these systems ran 24/7/365. I realise that nobody on this forum has the ability to do this at home, but it is the most reliable measurement of filtration efficacy. If you do want to investigate this further, airspeed velocity meters are cheaply available on Amazon…..
However, my experience and knowledge tells me that In infrequent home use a filter in this sort of application should have a much greater life than two months……the HEPA should easily outlast the carbon filter.
