Drew, it's not like this... About HEPA I rely in personal experience. Since I'm using that cheap desktop air purifier I don't know what dust is, and it's HEPA H13 class, from manufacturer specs.Originally Posted by Drew Wiley
Regarding air flows, also it's not about wiki, see the screen shots... I may tell you the kind of shrapnel I keep under skin about that...
I wish at least one of our 'experts' would document sources with hyperlinks. Saying 'google it' is not much help. The only source we are not supposed to link to is live eBay.
Most of us are not competitors, nor in business any longer.
Share with the class.
Tin Can
Pere - in the EU, many govt specs are beyond HEPA; it's another classification ten times finer than HEPA for things like cadmium, chromium, and lead dust than required in the US, but required here for radioactives (plutonium etc.) and viral biohazard labs. Desktop air purifiers are not true HEPA. In that case, it's just a marketing term. I have several of those and they are indeed useful. But the industrial version in my personal cleanroom would cost thousands of dollars to make today. It relies on banks of electrostatic copper panels and not just filter material. Gosh, Pere, I've equipped everything from heavy industry to nitpicky museum display shops with air cleaners. And again, HEPA legally means a sealed HEPA system, not just a comparably fine fabric inserted in something. That distinction might be meaningless in many home darkroom applications, or truly a life and death distinction to someone contemplating installing a lab or studio in an old industrial building, or adjacent to something like that.
Randy - the EPA has its own website related to such topics. I don't pretend to be an "expert". EPA licensing is tiered. Mine was the lowest level, appropriate to the kind of product distribution we did, mainly for lead paint abatement. We held classes where several thousand general contractors as well as painting contractors were certified to do their own work; and we did this in conjunction with someone licensed to certify industrial lead and asbetos abatement as well, who was in fact the main EPA inspector in the SF area. At the time, I managed the largest inventory of this kind of equipment in the entire US west of New England. True biohazard as well as radioctive control like LBL and Lawrence Livermore Lab required in-house specialists and a completely different degree of control, though I dealt with their facilities shops. I have known hundreds of people afflicted by toxic dust, including entire families with their health ruined simply because they happened to live across the street from some bootleg old building remodel. Our old naval bases and paint factory sites are even worse, but they're exactly the kind of locations art colonies gravitate toward.
Drew, tell me, is this true or false ?
"To qualify as HEPA by USA industry standards, an air filter must remove (from the air that passes through) 99.97% of particles that have a size greater-than-or-equal-to 0.3 µm"
My wife has had COPD since childhood. We run two separate room HEPA filter devices and have the same plus electro-static filtering in our central HVAC. It works, and BTW, my darkroom is practically dust-free.
Don't over-think this thing.
Oh, and pull the air through. Filter the intake source. Old joke: "Why is that guy pulling a chain down the street." "Well, ya ever tried to push one?"
Jac, I agree that's way easier to obtain a good ventilation by pulling: Less noise, less turbulence...
But if we place a filter in the input (to not throw dust in) then a fan in the input may be considered.
Good thought. A filter not necessarily with a fan on the input certainly would help!
Well, it can be a fan (in the input) that barely compensates the filter resistance, to prevent a negative presure than would allow to enter some air from uncontrolled paths, mainly when door is openned. If we open the door with exhaust fan working then several m3 of unfiltered air may enter in the darkroom, but if a fan is pushing enought throught the filter this won't happen.
Pere - False. "Industry standards" do not equate with EPA or EU specs which account for how the entire SYSTEM is sealed. There is a lot more involved than what you cite as "pass through". By analogy, you might have an otherwise perfectly good water hose, but if your fittings on each end are not tight and you turn on the water, there will be unintended spray. It also involves the kind of dust involved, i.e., its ability to erode right through or else corrode something related to the system. Let me repeat - merely containing an alleged HEPA filter element does not make necessarily something a HEPA device. Over 90% of items marketed as HEPA in this country do not match the EPA specification for that term. Nor do they have to unless they are misleadingly marketed for
those kinds of applications, which requires their own inspection and not that of UL. But again, whether or not this applies to a home darkroom all depends.
I'd hate to drop a bottle of chromium salts on the floor and pick the dust up with some phony-HEPA home center vacuum. That scenario could actually apply to a number of people here, not to others. I have a problem with concrete effluorescence on parts of on my lab floor, and it goes right through those phony HEPA vacs, scattering fine dust all over the place. A HEPA duct filter wouldn't do a bit of good. But a true EPA HEPA vac captures every bit of it. Due to her allergies, my wife borrows the real HEPA vac for the house after using one of our phony HEPA vacs first. Big big difference. ... Jac, I happen to make matched 8x10 separation negs replete with multiple masks at times relative to specialized color printing. When I do such things, the entire clean room is swabbed down in advance, and overthinking the problem is a helluva lot better than the option. Maybe you enjoy spotting, I don't. Back when I was doing big Cibachromes, which are electrostatic as hell and almost impossible to spot, the more obsessive one was about dust, the better. All it took was one piece of lint to ruin a $200 sheet. But I like your analogy about pushing a chain.
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