Re: [DIYbio] Re: low cost positive pressure laminar flow HEPA filtered box

On 07/28/2014 04:15 PM, CindyB wrote:
> If there is an outside to inside path for the water, the RH will rise.

Thanks for thinking about this. Water will always flow freely through a HEPA filter made
to filter 0.3 micron particles to a degree of 99.97% or 0.9997 fraction of all air going through it.
That means RH would not tell you about particle filtering ability.

I am interested in ways to use the industry standard filter characterizing measurement stats to show meeting them
for reasons of convincing others or your own group members your filter is adequate
without doing long term experiment design. Some may want to maybe do such long term experiments,
but they would never buy a filter that did not minimize the chance it would be to blame.
I'm wanting to sell filters, so characterizing them to compare price and performance with standards is
essential.

One industry standard about quality of construction of seams is to squirt an air suspension of
0.3 micron particles, (the hardest ones to filter out), at seams and count particles downstream,
noticing any spike of particles counted after spraying seams. That's what I am thinking of the
particle detector for.

Measuring the 0.9997 fraction sounds very difficult to do -- best left to labs for characterizing
filter fabrics.

Looking for spikes in time of particle counts while blasting the outside of a filter will show 2 defects
of manufacturing: A frame seam not sealed, or filter material that has been folded too sharply and broken through
so that particles go through a ragged tear in it. It will work even with a used filter.

For hood owners to have their own particle counter will help them
determine if their filter is damaged by rough handling, or if a new filter
has been installed loosely with a gap that is leaking dust. It will let
them break free of the "certified by X high priced seller" trap, since they can compare themselves
and so self certify.

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