Clean and Dirty HEPA filters

HEPA Filters, Fire, and other issues

HEPA stands for “High Efficiency Particulate Air”.  In terms of air-filters, these are the best of the best, the most efficient ones on the market.  Unsurprising, given their history – HEPA filters were originally designed by Arthur D. Little for use in the Manhatten project, to prevent radioactive contamination.

A HEPA filter is a series of fiber mats (often fiberglass) placed over each other randomly, so that the result is something like felt.  The aim to create holes no larger than 0.3 micrometers in diameter.  That’s another legacy of the atomic origins.  The most dangerous source of radiation was considered particles of 0.3 microns in diameter, hence this became the standard to check. This is worth knowing – HEPA filters may not stop all nanoparticles, and since basically no one knows anything about what dangers nanoparticles pose, double check this.  There are different standards of HEPA filters that block different amounts of pollutant.

The main place you’ll want HEPA filters is in your air-conditioning.  They prevent dirt getting in to your experiments and pollutants getting out.  See the previous point about nanoparticles: if you don’t want to get sued, this is worth controlling for.

HEPA Clogging and trouble

Where things can get ugly – very ugly – is that these things get clogged.  See featured image.  You know how a dryer’s lint filter get’s clogged?  Same thing.

Any self-respecting  lab air conditioning unit will be processing much higher volumes than your average dryer.  Just one of our units processes fifty thousand cubic meters of air each hour.  That’s a lot of air to carry a lot of dust.

If a HEPA filter gets clogged up, bad things happen.  First of all, it stops working correctly – that’s bad for fume hoods and similar, where now your researchers may be breathing in toxic crap.  If the filter get’s really clogged, it can tear loose, get tangled in the A/C mechanism and start a fire.  That’s just from regular dust – remember that a lab produces all sorts of novel dusts and vapours.  It’s not beyond the bounds of possibility for a clogged HEPA filter to develop nasty cross reactions.

Servicing and Alarms

To keep this at bay, all your HEPA filters need to be serviced regularly, and that needs to be further supported by an alarm system that warns when the filter is dirty.  Here’s an example of a HEPA filter.

Where this can get tricky is that you may not have direct – or any – control over these things.  If you are renting the space from someone else, whether it’s a University or a research institute, it may be their responsibility to check these things.  Which is fine, but if they screw up, it’s your researchers and workers who are sucking down poison fumes – and should you end up venting something toxic into the environment, it’s your ass in the legal sling.

So it is worth speaking with the local building management (or whomever) to make sure such measures are in place.  If at all possible, try to get yourself in the loop of alarms and warnings about dirty filters and servicing.  Nothing beats having your own eyes on the situation.


(featured image courtesy of the Stanley Subaru Scoop)

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