Darkroom Exhaust Fan(400 CFM) For Positive Pressure, Plus DR Design?

[Thalmees]

Darkroom Exhaust Fan(400 CFM) For Positive Pressure, Plus DR Design?
Hello everybody,
Thanks so much for providing your input.
This project is so important to me, appreciate all help in this matter.
Details:
I'm in the process of transfer to a new darkroom.
Just contemplating to fit two(2) exhaust fans, REVERSED, in the door of the darkroom, to create positive pressure. Each will be connected to a separate one(1) "On/Off" switch. Door will use the Automatic Closing Mechanism.
The other side of the door, is leading to a small corridor that leads to the rest of a very big apartment(house).
Will use another two(2) fans as exhaust(not inverted), above each other, separated by 30 inches, on the other side of darkroom, but on the other extreme of the same wall of the positive pressure fans.
Hope the drawing(below) is easier to understand.
One exhaust fan is equivalent to one of the positive pressure fans(400 CFM). The other is bigger(may be 1200 CFM). The bigger exhaust fan will be at bout 60" above the ground level, at the end of my sink.
Exhaust fans are pulling air into a vertical vent area inside the building(not house), that open at the top of the building.
Exhaust fans will work as a passive louvers when they are "Off". Both will be connected to one(1) "On/Off" switch.
Positive Pressure Fans, will work permanently. Or at least one of them.
Please assume every thing is light/air tight.
The room has two(2) windows, but will close them to prevent dust, unless it is seriously needed(do not know, so far).
I'm afraid of pressure gradient to be effective enough to do the job?
Room area: 21 ft X 15 ft X 9 ft(6.5mX4.5mX2.8m). BTW, 9 feet = 108".
Capacity of each each regular fan(2 positive pressure & 1 exhaust): 400 Cubic Feet Per Minute(400CFM).
Capacity of the bigger fan(1 exhaust): 1200 Cubic Feet Per Minute(1200CFM). But, I think this will effectively be 800CFM after making an efficient light tight hood around it.
Room Volum: 2835 Cubic Feet.
Which theoretically means, 7 exhaust fans Plus 7 positive pressure fans(or louvers), of the same capacity.
The original two(2) windows of the room(for air and light), will be closed, to be air/light tight, to prevent any possibility of dust accumulation. Any louvre or fan there, will destroy the shape of the building from outside.
Photos before summary:
Room Design including Inlet and Outlet of Air:

https://i.postimg.cc/gkhrK477/IMG_2626.jpg (https://postimages.org/)
.
Positive Air Fans & one Exhaust Fan Model:

https://i.postimg.cc/rmfz8gNm/IMG_2615.jpg (https://postimages.org/)
.
Tried to be organized, My apologies being long.
Summary:
So, I'm describing a darkroom design providing fresh air from inside house air(house is designed to provide maximum air/light ventilation, on demand), minimal or no dust could inter the darkroom.
And ventilating safely to a vertical vent area that connected at the top with air above the whole building. No other air ventilation leads to that same vent area in the building.
My query:
Drawback, potential problems, that I may missed?.
Or it's just a crazy idea?
Really wish to know how it will work, before doing more destruction.
Appreciate any input.
Best.

[Luis-F-S]

I think you are way over thinking this. The doran fan you're using, if you remove one of the louvers it goes from a 400 CFM fan to 800 CFM. If you're not discharging directly outside, you probably don't need the second louver, and you can always add it if needed.

Don't understand why you have the need to put two fans in series. I have two exhaust in parallel in my dark room, they both discharge to the same exhaust duct which goes outside. I have two intake louvers at the opposite end of the darkroom for cross ventilation.

If you want to put a positive pressure fan, I would switch it on when you're in the darkroom, and not leave it on all the time. At most I would put it in a timer if you feel you'd have humidity issues if not on. My darkroom has an AC vent, so it is always cool and humidity is not an issue. Hope this helps.

L

[angusparker]

My set up is two fans one for intake that pushes outside air from outside the house through a filter and then through louvers into the darkroom and the other to draw air out to an external vent on the roofline. The are both on the same switch and the same CFM.

I would say if you are drawing air from inside the house the intake fan is not necessary. What is key is the air path to come in above head height and to be drawn out from just over the trays far below nose height. You will most likely need a soffit and light tight louvers to get the air in across from the trays and uptake vent so you have positive air movement from top of back of your head to tray and out.


Sent from my iPhone using Tapatalk Pro

[Peter Collins]

For the space as dimensioned, you have too much fan power (as CFM) and thus air movement. I hope that you contemplate a rheostat/dimmer instead of a simple on-off switch. Thus, if you have too much air flow, you can reduce fan rpm. Consider, as well, separate switches for each fan; for very little extra cost, you can have a huge range of adjustment. Also--You just want to keep your breathing zone in fresh air, not necessarily the whole darkroom, and not your whole body.

You don't want so much air movement that you have turbulent flow in the darkroom. Something closer to laminar flow is ideal. If you have too much air movement through the fans, it will feel almost windy in the darkroom.

[Jim Jones]

I kept darkroom ventilation simple: a filtered louvered small fan forcing air into a small darkroom, and darkroom air leaking out wherever it could. This was satisfactory for many years. If the surrounding area had been living space, I would have sealed the leaks and let positive darkroom pressure vent to the house's outside.

[Thalmees]

... Hope this helps.
L
Thanks so much Luis. It is of great help.
Let me please try to understand what you mean exactly.

...,
if you remove one of the louvers it goes from a 400 CFM fan to 800 CFM.
...

There are four(4) fans, only, No louvres.
Two(2) Fans are fit on the door for Positive Pressure(intake). The other two(2) are on the other side of the same wall, for exhaust(draw air out). No passive louvres.
If I understand you correctly, you mean to take one Positive Pressure Fan from its sealed place in the door, leaving only the opening, beside the other working Positive Pressure Fan.
My apologies Luis if my understanding is not correct.
I think that will disturbs the Air Pressure Gradient. Plus, some light will leak from the corridor to the darkroom.
The same case for Positive Pressure Gradation, even if I replaced the Positive Pressure Fan, with a light tight passive louvre.
.


...
Don't understand why you have the need to put two fans in series. I have two exhaust in parallel
...

What actually happen, is connecting each two(2) fans in each area, to an extension power cable with individual "On/Off" switches. If I need two(2) fans to work together, will use the main switch, if I need only one(1) to work, will use the individual switch.
.


...
If you want to put a positive pressure fan, I would switch it on when you're in the darkroom, and not leave it on all the time.
...

I may settle on this solution.
But before that, I wish I can validate my primary design(or any better alternative) through this thread.
Until now, I do not know if inverting exhaust fans(to work as Positive Air Pressure), is appropriate or just arbitrary experimental?
Appreciate your input.
Regards.

[Christopher Barrett]

Good air exchange is definitely a good thing, but more importantly, you should make sure that the direction of air flow keeps the chemistry out of your nostrils and out of your lungs. For example, if you just install louvred exhaust fans into the ceiling, you'll be drawing contaminated air upwards, making it easy to inhale.

Ideally, you want a positive air supply in the ceiling with exhaust venting near the tops of the trays.

This is a good read on the subject... (http://sebastiandarkroom.com/darkroom_design.php)

A shot of my in-progress darkroom... positive supplies across the room in the ceiling with exhaust venting 20" over tray tops, ducted out of the bldg.

http://christopherbarrett.net/wp-content/uploads/2018/10/darkroom.jpg

HTH,
CB

[Tin Can]

I am about to put ventilation in my 'spare bedroom DR' and this thread is making me rethink my plan.

Jim Jones suggests positive room pressure. I have read many that suggest that. Seems good.

My DR is 140 sq ft, 1400 cubic ft. In a very leaky house.

My last DR was in a corner of a 750 sq ft and 9000 cubic ft, open space. A very airtight loft on sealed cement slab. 6 years ago I installed one Panasonic 240 cfm fan (https://shop.panasonic.com/support-only/FV-20NLF1.html) venting from the top of my fixer tray area and outside.

It vented, but seemed weak. I added floor level intake air opposite the sink. That increased exhaust air volume a lot. Fresh air came in, pulled up off the floor, over the sink edge and across the fixer out to the street. Tested with cigarettes. I don't smoke.

I plan to buy the same fan again and install it similarly but my intake air will come from the main house. I currently run a Merv 16 filter on the house HVAC, will add another Merv 16 intake air filter for the intake house air supplying the DR. And as Pere suggests a Honeywell Hepa filter inside the DR.

Dust is the enemy.

I don't see a good way to use positive pressure.

Let's discuss OP further.

[Luis-F-S]

Thanks so much Luis. It is of great help.
Let me please try to understand what you mean exactly.

I may settle on this solution.
But before that, I wish I can validate my primary design(or any better alternative) through this thread.
Until now, I do not know if inverting exhaust fans(to work as Positive Air Pressure), is appropriate or just arbitrary experimental?
Appreciate your input.
Regards.
You can invert a fan to blow into the room. I did that in one of my darkrooms. If you want to use 4 fans, I would put the on individual switches. I have rheostats on mine, also made by Doran and seldom run them full speed. I would certainly do this on the exhaust fans. On the intake fans, you can run both of them off one rheostat. I got mine at KHB in Canada and they've worked like a charm.

On the exhaust fans, if you're not exhausting to the great out doors (lots of light) consider removing one of the set of louvers as it doubles the output.

Just don't go crazy with it and don't loose any sleep over it. There is a thread in here on my fan setup. See:

http://www.largeformatphotography.info/forum/showthread.php?107412-Darkroom-Design-for-a-9-8ft-x-10-1ft-room/page2

You can see photos of my three darkrooms on:

http://www.largeformatphotography.info/forum/showthread.php?56044-Lets-See-Your-Darkroom/page51

L

[Pere Casals]

Darkroom Exhaust Fan(400 CFM) For Positive Pressure



Honeywell Hepa filter inside the DR.


This is my view

IMHO we have two goals for the darkroom air:

> removing odors and potentially dangerous fumes.

> removing dust from air

If we use "safe" chem like Xtol and Dektol then a basic HEPA air purifier solves the dust. But if a pocess provocate toxic fumes then the HEPA won't remove it.

If we want to vent the darkroom I'd only place a fan (of the necessary power) with an HEPA filter introducing air in the room, and the exhaust would be trought a light tight vent. I don't see the need to install a second fan in the exhaust outlet.

The HEPA filter in the input fan should be covered with a regular foam (easy to clean) to remove the large particles, in this way the HEPA filter will last more.

IMHO the air intake should be adjustable (a cheap $10 voltage regulator for motors), delivering an small flow when we work with safe chem, because excessive flow will only bring on problems(noise, dirt in fiters), in that way when we work with more dangerous chem we can still vent what necessary.

IMHO internal dust has to be removed by a regular HEPA air purifier, and we have to input an HEPA purified fresh air flow depending on the kind of chem we work with.


We have to remember that the most common hazard in darkrooms is fumes from acetic stop bath, if using plain water or a citric bath then our venting requirements may decrease a lot.


https://silveronplastic.files.wordpress.com/2017/10/the-darkroom-cookbook-3rd-ed-s-anchell-elsevier-2008-ww.pdf

page 103: "The fumes which emanate from acetic acid stop baths are perhaps the single greatest health hazard in the darkroom"
page 3: speaks about ventilation

[Tin Can]

I use water for film stop, mix my own citric acid for paper stop.

I use only TF5 mixed with distilled but in separate containers. I don't mix the fix betwixt film and paper.

Up to now I used Rodinal on all film. Ilford PQ for paper.

Most LF film is processed in covered tanks with Gas Burst.

I won't mix any powder inside the DR, I have a shed if that comes up.

Too many dead friends from Industrial Disease (https://youtu.be/g3X3rKtruSg) at ye olde factory. Not kidding. At least one refused to use the readily available high power vent hoods.

[Thalmees]

...
I would say if you are drawing air from inside the house the intake fan is not necessary. What is key is the air path to come in above head height and to be drawn out from just over the trays far below nose height. You will most likely need a soffit and light tight louvers to get the air in across from the trays and uptake vent so you have positive air movement from top of back of your head to tray and out.
...

Thanks so much angus.
Great help.
As for passive air inlet(or passive light tight louvres) instead of active Positive Pressure Fans, it could help in better exhaust flow, but I do not think this will help the purpose of the design.
I adopted the Positive Air Pressure because I believe it's the best way to get rid of dust.
Then, I chose Inhouse Air(instead of outside Air at window area), because Inhouse Air is clearly much less dust born, plus the fans are high in the door well above the ground level of the house. I do not know so far how can I get filters that could fit in Doran fan?
As for the pressure gradient, I revisited my primary design, thanks.
Please see the drawing below, thanks everybody for the comments.
The intake fans will be at least 72" above the ground of the room, this is the maximum usable height for the door, but will use angled 6" tube(Doran specific size) to direct Positive Pressure Air up higher than the level of the door(up to 100" above room ground level, as needed, but I will consider not to add much of dead space[tube length] to conserve power of positive air flow).
At the same time, I owered the level of the bigger Exhaust Fan to be 50" from ground level. Planning to make the sink low to approach it on a chair, which the case for all smaller prints.
Appreciate your input angus.

https://i.postimg.cc/ZKMBVbp5/IMG_2637.jpg (https://postimages.org/)
Intake door fans can be extended higher than 72"

[Thalmees]

For the space as dimensioned, you have too much fan power (as CFM) and thus air movement. I hope that you contemplate a rheostat/dimmer instead of a simple on-off switch. Thus, if you have too much air flow, you can reduce fan rpm. Consider, as well, separate switches for each fan; for very little extra cost, you can have a huge range of adjustment. Also--You just want to keep your breathing zone in fresh air, not necessarily the whole darkroom, and not your whole body.
You don't want so much air movement that you have turbulent flow in the darkroom. Something closer to laminar flow is ideal. If you have too much air movement through the fans, it will feel almost windy in the darkroom.
Peter, thank you so much.
Thought my self minimalist.
Do you think the upper Exhaust Fan is needed?
Thanks for suggesting individual switch for each fan plus rheostat/dimmer. Will consider that seriously.
As for the volume of air flow, the Intake Fans can provide 800CFM without filters. The lower and bigger Exhaust Fan, can pass 800CFM after making the appropriate louvre. Not considering the upper Exhaust Fan for awhile only.
But wait! The room volume is above 2800 CF. Which means around seven(7) equivalent fans to clear that volume in one(1) minute. Just divide 2800CFM by 400CFM, for one(1) minute.
I only have two(2) in each side, which means it takes about 3.5 minutes to clear complete room Air in one cycle. Adding the upper Exhaust Fan, will decrease the time maybe to 2.3 minutes. Of course assuming overload on the intake fans or more sufficient air going into the room.
Honestly, I do not know if that times are low(fast) for an efficient air flow in a darkroom?
Please let me know if I have a mistake.
Thanks so much Peter.

[Thalmees]

I kept darkroom ventilation simple: a filtered louvered small fan forcing air into a small darkroom, and darkroom air leaking out wherever it could. This was satisfactory for many years. If the surrounding area had been living space, I would have sealed the leaks and let positive darkroom pressure vent to the house's outside.
Thanks Jim for your input.
That was the situation for me some time in the past.
Succeeded in Exhaust but failed in creating positive pressure. That resulted in a lot of dust.
Regards.

[Thalmees]

...
Ideally, you want a positive air supply in the ceiling with exhaust venting near the tops of the trays.
...
HTH,
CB
Thanks so much Christopher for your input and for sharing the photo of your DR and link.
It's not only correct, it's the ideal.
Originally, my room was finished constructed as a living room, and do not wish to do more destruction.
In the next phase after installing every thing and trying what I'll settle on from this thread, will consider flexible ducts to bring the Positive Air to the opposite corner of the Exhaust fans.
As for recommending against putting Exhaust Fan high in the ceiling, do you think that the upper Exhaust Fan is actually needed? Drawing of the wall that faces the enlarger, is in post# 12.
Regards.

[Thalmees]

Outside the concern of this thread and as for my current darkroom.
Do not know actually, who is sharing whom?
Dust(a lot of it), lizards, cockroaches, snakes, mice , more than one species of ants and other incredible creatures, are continuously(some are on/off hopefully) sharing me(effectively, I'm sharing them) the darkroom, for the past several years.
It's one(1) meter below the house ground level room, with 3 walls facing empty lands. The ceiling is another horrible story.
My trick to make a positive air pressure, has failed few weeks after it started.
Among all enemies and friends sharing the room, dust and static electricity are the biggest.
With all limitations around the future DR, I wish really to reach the best possibilities for an efficient permanent DR, through this forum.
Regards.

[Thalmees]

...
Jim Jones suggests positive room pressure. I have read many that suggest that. Seems good.
...

Hello Randy,
Thanks so much for your post.
Thanks for confirming that the best strategy to fight dust, is Positive Air Pressure.
That's the reason why I did not consider passive louvres instead of active Positive Pressure Fans, in my primary design.
Regards.

[Drew Wiley]

The secret is to pull air, not push it. If you get a big OUTDOOR wall-mounted Broan squirrel-cage from Grainger, it will isolate both noise and work far more efficiently than an indoor push fan. If you must do it indoors, an IN-LINE Panasonic squirrel-cage will cost you around $400 but also be quiet. Avoid rotary fans (noisy). I strongly recommend a high-quality unit which accepts a dedicated speed control (around another $40). Of course, you'll need light-tight air intake vents like Doran offers; forget their fans. Air should be pulled from behind across the sink toward a wall vent or suitable fume hood. Duct size and smoothness has to have matching efficiency, though configured to prevent light from entering via the exhaust fan. One good exhaust fan is better than a bunch of cheap ones. Air filters or purifiers won't do it by themselves, though they are nice for dust control in film-handling and enlarging areas.

[Pere Casals]

The secret is to pull air, not push it.

It's nearly the same, for each one liter of air you pull another one will enter, and for each liter you push one will exit. And the fan will make the same effort in one case than in the other one.

If pushing the air inside then the flow entering is more turbulent (because the fan), this helps venting better all the room space. If pulling we vent more the area close to the outlet.

If we push the air in... then the outlet vent (having no fan) will take the air around it in the same way that if we were pulling the air... but the higher turbulence will mix more all the air inside.

Another difference is that if we push filtered air inside then we have an slight positive pressure inside, preventing some dirt intake from uncontrolled paths, this is the principle used in Cleanrooms: https://en.wikipedia.org/wiki/Cleanroom , this is good for darkrooms.

In case of Biocontainment rooms it's the counter, negative pressure is ensured to prevent "dirt" from the inside escaping to the outside, so the air is always pulled and filtered (or Sterilized) before reaching the outside.


So, if we have trays not exactly under the outlet then pushing looks better.

[Drew Wiley]

Here you go again, Pere. You're guessing. I actually have decades of experience distributing fans, including the entire line of Panasonic, and have specified all kinds of applications, including not only private darkrooms but commercial photo labs and all kinds of scientific research facilities. Within walking or bicycle distance of my former office and warehouse were some of the biggest pharmaceutical, biotech, and university research labs in the entire world. An everyday issue for me. My own big squirrel cage outside my sink room has been running quietly and flawlessly for forty years now. A good investment. You need to understand things like hydrostatic pressure related to humidity, air friction in the ducting etc. The only problem with my exterior fan is that every few years wild bees try to make a hive in it - so I have to leave it running a few days to discourage them ! In my house I use a Panasonic in-line duct fan instead, for the bathroom shower steam, which pulls the air all except for the last few feet to a roof exhaust cap. Really nice and super-quiet. I also have an actual clean room in my lab, separate from the sink & processing room. It has a big electrostatic air cleaner. If biohazard is potentially involved, what on earth are you developing in that darkroom anyway, film from the Andromeda Strain satellite ???

[Thalmees]

You can invert a fan to blow into the room. I did that in one of my darkrooms. If you want to use 4 fans, I would put the on individual switches. I have rheostats on mine, also made by Doran and seldom run them full speed. I would certainly do this on the exhaust fans. On the intake fans, you can run both of them off one rheostat. I got mine at KHB in Canada and they've worked like a charm.
On the exhaust fans, if you're not exhausting to the great out doors (lots of light) consider removing one of the set of louvers as it doubles the output.
Just don't go crazy with it and don't loose any sleep over it. There is a thread in here on my fan setup. See:
http://www.largeformatphotography.info/forum/showthread.php?107412-Darkroom-Design-for-a-9-8ft-x-10-1ft-room/page2
You can see photos of my three darkrooms on:
http://www.largeformatphotography.info/forum/showthread.php?56044-Lets-See-Your-Darkroom/page51
L
Thank you so much Luis for your kind followup reply. Appreciate it.
I encourage other kind posters to reply to my queries and thanks so much.
Few important points has been confirmed essential. Individual switches, rheostats, highest possible level from the ground for the Intake Air and lowest level possible for the Exhaust Fan.
But still few points also.
1. Why I should not use Positive Pressure Fans "On" all the time?
I know it has a limited life span, but I do not think it's short.
Plus, how can I make sure that no dust(or minimal) will inter the DR?
2. How many fans are enough?
Operated one new Doran fan in my hands, just to see if it's working or not and to test the Air Flow Speed/Volume. I found it not that powerful! The fan is new, but the air flow speed was not that much!
Knowing that my room is more than 2800CF, I concluded it's too weak to create the required Positive Pressure for the given room air volume.
That's the reason why I used two(2) Positive Air Pressure fans in my primary design.
Could not expect appropriately what's the effect of one fan on 2800CF after it installed in place?
3. Is the upper Exhaust Fan necessary?
As far as I know, if intake air is 800CFM, Exhaust should be a little more.
Is that correct?
Appreciate your input.

[Pere Casals]

Here you go again, Pere. You're guessing. I actually have decades of experience distributing fans, including the entire line of Panasonic, and have specified all kinds of applications, including not only private darkrooms but commercial photo labs and all kinds of scientific research facilities. Within walking or bicycle distance of my former office and warehouse were some of the biggest pharmaceutical, biotech, and university research labs in the entire world. An everyday issue for me. My own big squirrel cage outside my sink room has been running quietly and flawlessly for forty years now. A good investment. You need to understand things like hydrostatic pressure related to humidity, air friction in the ducting etc. The only problem with my exterior fan is that every few years wild bees try to make a hive in it - so I have to leave it running a few days to discourage them ! In my house I use a Panasonic in-line duct fan instead, for the bathroom shower steam, which pulls the air all except for the last few feet to a roof exhaust cap. Really nice and super-quiet. I also have an actual clean room in my lab, separate from the sink & processing room. It has a big electrostatic air cleaner. If biohazard is potentially involved, what on earth are you developing in that darkroom anyway, film from the Andromeda Strain satellite ???

Drew... tell me, what advantage has pulling air compared to pushing air ? don't tell me that's not exactly the same flow amount...

Single difference is that if pushing you may have the turbulence generated by the fan inside the darkroom, while if pulling the that turbulence is generated in the outside.

But when placing an HEPA filter in the intake (after the fan) that turbulence is reduced to a minimum. Well, you may know that all cleanrooms are pushing air, or not ?

[Pere Casals]

This is a simulation of what will happen with the air flow in the Thalmees' darkroom.

Today it's quite straight to make an accurate flow simulation that will tell the trajectories of the air and the air speed in each spot of the room.

This is usefull to see if nasty loops are formed or if critical areas are well cleared from fumes without contaminating the rest of the room.


https://c2.staticflickr.com/2/1940/43374448920_889c6b432e_b.jpg

https://c2.staticflickr.com/2/1930/43374449060_dba1e8dfe4_o.jpg

https://c2.staticflickr.com/2/1906/44466056774_2eab94e498_o.jpg

https://c2.staticflickr.com/2/1954/43374449120_46074d5323_o.jpg




What I see in that design is that inlet flow has too much energy in the inlet flow and this ends in a not enough smooth flow over the trays.

No problem with non toxic fumes, but for hazardous fumes the flow should go more direct from the trays to the outlet.

So in that case it would be better to remove the fans in the inlet.

Pushing air can be a suitable choice, but one have to be careful with the inlet speed.

[Thalmees]

Hello Pere,
Appreciate your input in the subject, thanks so much.


...
a basic HEPA air purifier solves the dust.
...

That's great idea really.
In my current dusty DR, I use two(2) small Honeywell plus one(1) bigger but slimmer Panasonic air purifiers. Each one of them has ionizer in addition to HEPA filter. My current DR is about 600CF, BTW!
https://i.postimg.cc/7hgj0CMQ/IMG_2642.jpg (https://postimg.cc/4Hx8Tx0z)
But, if your DR is not well air tight and surrounded by small but frequent whirlwinds, from three(3) sides, this trick will turn like a joke. Even if you controlled the few meters in front of DR door.
In my next DR, I believe it will do a great job.



...
If we want to vent the darkroom I'd only place a fan (of the necessary power) with an HEPA filter introducing air in the room, ...
The HEPA filter in the input fan should be covered with a regular foam (easy to clean) to remove the large particles, in this way the HEPA filter will last more.
...

This is the best idea in your post Pere. Thanks.
Please let me know more about HEPA for intake fans, from where can be provided?
Then, does the HEPA filter reduce the Air Flow? I think so.
It's already 800CFM for 2800CF room!
Which means 3.5 minutes to clear all room volume in one cycle.
I can imagine that HEPA filter could reduce air flow from 800 to maybe 200CFM.
I do not know what's the best air exchange volume(flow rate) in a typical DR?
But I feel it's more than to be covered by 800CFM fans, let alone by 200CFM.
.


...
and the exhaust would be trought a light tight vent.
...

Thanks for your suggestions.
That is the passive(fan free) louvre.
But, honestly, I could not answer my self:
Why no fan in the exhaust area in the first place?
Why just passive louvre is enough?
.


...
I don't see the need to install a second fan in the exhaust outlet.
...

Considering volumes and flow rates mentioned above, How did you reach to conclude that one(1) Exhaust Fan is enough?
When I built my current DR, several years ago, the situation was just arbitrary. I chose the biggest possible fan for the Exhaust and made the biggest hood(light tight louvre) in Mankind history for that fan!
In my next DR, I hope to do everything methodological as possible.
.
Appreciate your comments Pere.
Regards.

[Thalmees]

This is a simulation of what will happen with the air flow in the Thalmees' darkroom.
...

What a happy surprise after I upload my last previous reply.
Thanks so much Pere.
Please use: https://postimages.org , to upload the images again.
It's free and provide bigger images.
After upload, select the copy sign of: "Hotlink for forums", in the right side, then paste it like text, each code/image in a line.
My apologies if you find inconveniences.
Regards.

[Drew Wiley]

Pere - there's an entire trade devoted to this kind of work. Any of the major fan manufacturers will offer some sort of catalog or website primer in the ABC's. In most situations you need about twice the CFM rating you think you will in order to get the net amount after ducting friction and hydrostatic pressure losses. And in terms of installation fuss and maintenance/replacement cost, one serious fan is going to be a bargain compared to a bunch of so-so ones on toy rheostats. And until you understand certain basics, all those hypothetical charts you give are meaningless. A large squirrel cage on a solid state control will run efficiently at even very low speed - very helpful is one is doing ordinary developing versus, for example, an accidental spill of glacial acetic acid requiring a sudden dramatic increase of exhaust. A push propeller fan suitable for this would be at least twenty times as many decibels of noise as a pull or inline squirrel cage. Again, just go to a big HVAC catalog like Grainger to compare specs and prices (their pitiful website gives only a partial selection). Questions to
ask in advance : 1) cubic footage of the darkroom space to be vented; 2) general climate (rain, humidity,etc); 3) how is the space heated or air conditioned; 4) how is your anticipated duct network going to be configured, duct type, diameter, and length ?

[Pere Casals]

Please let me know more about HEPA for intake fans, from where can be provided?

I'd use an spare filter in a DIY casing, for example Amazon has ($23) an Surround Air MT-8400SF spare filter, larger than 10".

In fact I do that in a drying cabinet for dry plates.


Why no fan in the exhaust area in the first place?

I'd only place a single fan, for input or for output. If placed in the input then IMHO the duct should have a large section to not generate too much turbulences, my guess is that a more laminar flow is better, also an HEPA filter will help with the turbulence.



Considering volumes and flow rates mentioned above, How did you reach to conclude that one(1) Exhaust Fan is enough?

In a kitchen you can generate a lot of smoke and that's solved with a single 250 CFM extractor, but the flow it's quite smooth and well designed and placed just abobe the smoke generation. Perhaps a kitchen extractor is an option...

A too high flow would bring on problems with air heating/conditioning/filtering...

[Pere Casals]

1) cubic footage of the darkroom space to be vented; 2) general climate (rain, humidity,etc); 3) how is the space heated or air conditioned; 4) how is your anticipated duct network going to be configured, duct type, diameter, and length ?

Drew, those were the preliminary calculations...

When we have potentially toxic emissions we may want to know if the flow in the room moves the emissions directly to the outlets or if the trajectories mix the emissions with all room air before making its path the exterior. In the former case we can completely avoid operator exposure to the chem with a lower flow, in the second case operator will have some exposure even in the case we use a high flow.

We can use smoke from a bare cigar to see in practice if fumes lighter than air are making its path directly to the outlet, and we can use dry ice fumes to see is heavier than air fumes are also making it's path directly to the outlet.

183161

This is a way to know if our operator is exposed to toxicity hazards, there are more ways based in samplig the air to fullfill labour regulations...

But when air samples have contamination (in case of labour regulations) then exploring the actual trajectories (with heavy and light smoke) and simulation software is the way to solve the problem.

[Drew Wiley]

Give it a bit of heavy rain or subtropical humidity, and an ordinary kitchen range hood would be quite weak, esp given the fact the duct might need a diverted path to keep light out. It's obviously better than nothing above a small sink, but nowhere near powerful enough to split into an extraction manifold or boost in case of an emergency spill. 250 CFM is marginal. At the 50% typical resistance loss I referred to, that's no more powerful than a cheap shower fan. With a 10 ft sink, I like around 750 CFM of pull with dedicated speed control. Or around 450 would be suitable for a smaller station. Again, pull, don't push air for maximum efficiency. Industrial rules for toxic emissions are a completely different subject. Real HEPA filtration is in an utterly different price league than that toy stuff referenced at Amazon, and you certainly don't need it in a typical home darkroom. It is nice to have in a clean room where film is loaded into either film holders or enlarger carriers.

[Pere Casals]

an ordinary kitchen range hood would be quite weak / esp given the fact the duct...

Drew, a kitchen extractor is heavy duty gear, sometimes my wife roasts an entire bison under it... of course it clears an small surface...

The duct can go directly to a light tight trap and exit...



250 CFM is marginal. At the 50% typical resistance loss I referred to, that's no more powerful than a cheap shower fan. With a 10 ft sink, I like around 750 CFM of pull with dedicated speed control. Or around 450 would be suitable for a smaller station.


I agree with those numbers, of course, but as I want filtered air I want to keep the flow at a minimum while breathing only fresh air, with those requirements a more refined design is needed, then it's necessary to understand how the flow travels inside the room, flow lines have to go from trays to the outlet, without intermixing inside the human populated area.




Again, pull, don't push air for maximum efficiency. Industrial rules for toxic emissions are a completely different subject.

Push and Pull should have exactly the same flow volume efficiency, the difference is that if pushing (without care) we may generate turbulence that wont allow a direct flow from the trays to the outlet...

Industrial rules enlights what we should do in a darkroom to breath fresh air only. I'm not speaking about environmental emissions, but about safety in the workplace.



Real HEPA filtration is in an utterly different price league than that toy stuff referenced at Amazon, and you certainly don't need it in a typical home darkroom. It is nice to have in a clean room where film is loaded into either film holders or enlarger carriers.

My cheap Honeywell 16000 purifier is HEPA class H13, this is removing at least 99.97% of airborne particles of 0.3 micrometers (µm), this is an amazing filtration for a darkroom, any commercial HEPA spare filter intended for home air purification is quite good because it's intended for people suffering allergies (pollen...).

But IMHO we should use a double system, this is filtrating entering air, and and recirculating the inner air with a purifier to deal with particles we generate from clothes and skin.


_____


To check the quality of our ventilation system we only need a Puro Habano, best suited gear for calibrations is a Cohiba Behike. It will show how the flow behaves and if the flow takes the fumes directly to the outlet or if the fumes walk around in our darkroom.

I'd would warn to not smoke it. That's specialized gear for calibrations only.

[Thalmees]

The secret is to pull air, not push it. If you get a big OUTDOOR wall-mounted Broan squirrel-cage from Grainger, it will isolate both noise and work far more efficiently than an indoor push fan. If you must do it indoors, an IN-LINE Panasonic squirrel-cage will cost you around $400 but also be quiet. Avoid rotary fans (noisy). I strongly recommend a high-quality unit which accepts a dedicated speed control (around another $40). Of course, you'll need light-tight air intake vents like Doran offers; forget their fans. Air should be pulled from behind across the sink toward a wall vent or suitable fume hood. Duct size and smoothness has to have matching efficiency, though configured to prevent light from entering via the exhaust fan. One good exhaust fan is better than a bunch of cheap ones. Air filters or purifiers won't do it by themselves, though they are nice for dust control in film-handling and enlarging areas.
Drew, thank you so much for your input.
Will consider which the best, pull or push air.
That needs further search. But, I could not alter any thing outside the building. It's already covered except the windows.
Plus, it looks that there is an implied agreement in this thread that four(4) fans is too much.
As for tools for air flow management, I already have purchased most things. Doran fans and Doran passive louvres.
But wait, all bathrooms in the same building are equipped by fans like the one you mentioned(hidden in the ceiling). Yes, maybe weaker, but stronger ones are available locally.
The best working thing in my current DR, is the Exhaust Fan. It's much much bigger than the fan in my house kitchen. But, yes it's very noisy.
With an area four(4) times the area of my current DR, I think the noise will be much decreased.
Thanks so much for your input Drew.

[scheinfluger_77]

Great discussion. The one thing not addressed (unless I missed it) is appropriate changes per hour in the darkroom. I am not an HVAC person so can’t speak to this. I have read (sadly I do not remember where) under normal circumstances 5-6 changes/hour are sufficient. Presumably this would mitigate the need for larger, more powerful systems.

[Thalmees]

This is a simulation of what will happen with the air flow in the Thalmees' darkroom.
...
...
...
...
What I see in that design is that inlet flow has too much energy in the inlet flow and this ends in a not enough smooth flow over the trays.

Pere, thanks so much taking the subject to this level of depth.
Please study the following drawing.

https://i.postimg.cc/hvpnRhyw/IMG_2645.jpg (https://postimg.cc/wRyZhxdc)
In reality, there is big negative pressure around the Exhaust Fan(or Fans). That leads to gradual increase of the Air speed(velocity) toward that area, regardless of directions and air pathway.
It's not the case with your computer drawings!
I think the computer assumed no ventilation or passive light tight louvre, at the Exhaust Area.
As for "enough smooth flow over the trays", specifically, please read my next comment.
.


...
not enough smooth flow over the trays.
...
the flow should go more direct from the trays to the outlet.
So in that case it would be better to remove the fans in the inlet.
...

Assuming your computer drawings are accurate, there is maybe better solution than removing the Intake Fans or just using passive light tight louvres.
How about decreasing the height of Intake Fans(in the DR door) to be just above the level of the sink height. In this case, the Fans should be vertically adjacent(not like before, horizontally adjacent). Then, using an "L" shap 6 inches tube, for each Fan, to direct the air toward the sink area?
There is agreement on using rheostats and individual switches. Calibration of the flow, is another later phase.
I think this can solve the problem of your computer drawings.
For my imagination, I think the corner facing the door(which is the opposite and farthest area from the Exhaust area), should has more air pressure to create gradient toward the other corner(Exhaust corner). That could be achieved by directing the air of only one(1) Intake Fan the same as before(toward the corner facing DR door).
The other Fan, will be as above, an "L" tube toward the sink.
Please let me know what do you think Pere. New drawing of the wall facing the enlarger is below.

https://i.postimg.cc/Dy268PnV/IMG_2646.jpg (https://postimages.org/)
The lower Exhaust Fan is effectively around 800CFM or lesser, after making appropriate light tight hood(louver).
The reason I insist on two(2) Intake Fans, is the dust control which could be achieved by Positive Pressure better than any other methods. Any later problem of the air flow, can be managed by individual switches and rheostats.
.


...
...
Pushing air can be a suitable choice, but one have to be careful with the inlet speed.
My apologies, the words "Pushing" and "Pulling", has been used more than once by more than poster in this thread. It's important.
Used alone, has no user location reference.
I think, both words could be used followed by either "to" or "from", to give a clear meaning for any reader imagination.
Like "Pushing to" or "Pulling from". Likewise for "Pushing from" or "Pulling to".
.
Pere, I really appreciate your input and depth.
Thank you so much.
Regards .

[Thalmees]

Great discussion.
...

Thanks so much to the selfless, expert forum members.
I really appreciate their posts in all subjects not only this thread.
.


...
The one thing not addressed (unless I missed it) is appropriate changes per hour in the darkroom.
...

Thanks so much scheinfluger for your post.
I asked about this issue, or just commented on, in posts 24 & 13 at least.
What I understood from getting No answer or No comments about this specific issue, is that I'm badly under estimating the effect of Intake Fans on the Air Flow.
Hope one of the members could comment about this issue.
.


...
under normal circumstances 5-6 changes/hour are sufficient. Presumably this would mitigate the need for larger, more powerful systems.
Thanks for sharing the information.
With simple calculations, 5-6 changes/hour is 10 to 12 minutes for each cycle.
My primary design, is much faster than that(3.5 minutes per 1 cycle), but honestly do not know if that good or bad?
Please review my previous post.
Regards.

[Jim Jones]

An important consideration is the darkroom worker's tolerance for polluted air. I've printed for hours in a small darkroom with no forced ventilation, but I grew up on a farm where the neighbor's barnyard spewed its own type of pollution when the wind was in the wrong direction. With enough motivation we can tolerate almost anything.

[Tin Can]

All I can add is how many air changes are way too much.

Our factory tested running engines in six 1500 cf cells. Our self designed system did 10 changes a minute. It was very loud and windy. We also had a big Halon (https://pubchem.ncbi.nlm.nih.gov/compound/Bromotrifluoromethane#section=Top) tank that would fire with a 20 second delay. We pushed air down to floor and sucked it out from top. We also had floor suction with shutoffs. Gasoline.The whole system shutdown when the Halon fired. Get out now. I set off the Halon 2 times by manual release. Antifreeze burns in contact with 1800 F exhaust.

I don't miss working there.

According my math a 250 cfm Panasonic moves 6 changes per hour. It is very quiet and located in the next room.

I listed my chemistry in a earlier post, as I think safer poison is safer.

Everything we do in a DR is about dilutions. Air and liquid.

[Pere Casals]

An important consideration is the darkroom worker's tolerance for polluted air. I've printed for hours in a small darkroom with no forced ventilation, but I grew up on a farm where the neighbor's barnyard spewed its own type of pollution when the wind was in the wrong direction. With enough motivation we can tolerate almost anything.

Depending on chem, no problem. Hidroquinone and P-Aminophenol (rodinal) are also used in cosmetics. Most fixers are salts, silver content in a used fixer is what's more toxic. The stop bath is a kind of vinegar...

But color chem is not as safe, and for BW I use dichromate for reversal... Depending on what we do in the darkroom we have to be careful...

[Pere Casals]

Please study the following drawing. In reality, there is big negative pressure around the Exhaust Fan(or Fans). That leads to gradual increase of the Air speed(velocity) toward that area, regardless of directions and air pathway. It's not the case with your computer drawings!

If you see the image, at left, Radiobutton "entrada" (input) is checked. This is the lines describe the path of the particles entering, if checking "Salida" (output) then you would see the paths arriving to the output, it's the same but it looks different because the lines that are uniformly selected to be viewed.

For a project, I had been 6 months all day long, becoming crazy, simulating fluids. I near needed therapy after that :) This is a simplified (Express) version of a simulator... with the full version it would be easier to show it.





should has more air pressure to create gradient toward the other corner


In this application there are no static pressure gradients in the room, only an slight difference in the input/output ports. Air is not substantially compressed, it's all about dynamics, we have fluid particles moving and having inertia.





There is agreement on using rheostats and individual switches

Rather than rheostats this is speed controllers, solid state...




"Pushing to" or "Pulling from"

...it's very well understood, pushing is a fan in the inlet...




For my imagination, I think the corner facing the door(which is the opposite and farthest area from the Exhaust area), should has more air pressure to create gradient toward the other corner(Exhaust corner). That could be achieved by directing the air of only one(1) Intake Fan the same as before(toward the corner facing DR door).


Let me make a simulation...

[Thalmees]

Ok,
It is a great brainstorming to me so far.
Not at all similar to solving problems around Photographic Exposure or selecting the best Methodology for Developing a Film. I confess.
Ilford Photo has answered the question about the air flow rate with greater certainty. Thanks Ilford Photo.
Please visit URL: https://www.ilfordphoto.com/faqs/health-safety-faqs/ , or read the quoted text below.


From: https://www.ilfordphoto.com/faqs/health-safety-faqs/
WHAT VENTILATION DO I NEED IN MY DARKROOM?

Smells and fumes from darkroom chemicals and heat from enlargers and lamps are best eliminated by some sort of extract in the room OR by opening the room up between processes.
If you are going to be in a darkroom for longer lengths of time it is useful to set up an extract fan with some sort of light proofing (baffles/black drapes, long duct) which still allows airflow. Also, cover your photo chemicals when not in use (trays/tanks etc.).
With these precautions, you will be able to remain safe and comfortable within the darkroom.
THE FOLLOWING EXTRACT IS AIMED AT COMMERCIAL/EDUCATIONAL DARKROOMS AND WILL GIVE YOU AN INDICATION OF WHAT IS REQUIRED.

This is the UK Industry recommendation and is from a document called:
"Heating, ventilating, air conditioning and refrigeration. CIBSE Guide B"
( CIBSE = Chartered Institution of Building Services Engineers)
"Darkrooms (photographic) 6-8 ACH (but heat gain should be assessed)
2.3.24.4 Darkrooms (photographic)

Small darkrooms for occasional use or for purely developing processes may often be ventilated naturally
with a suitable light trap, although consideration should be given to providing mechanical extract using an air
change rate of 6 to 8 air changes per hour. For general purpose darkrooms, however, the air change rate should
be ascertained from a consideration of the heat gain from the enlarger, lights etc. plus the occupants, on the basis of
a temperature rise of 5-6 K. In industrial and commercial darkrooms that have machine processing, the machines
will very often have their own extract ducting, the air supply being drawn from the room itself. It will usually be
necessary to provide a warmed and filtered mechanical inlet in such cases. In special cases, involving extensive
washing processes, the humidity gain may be significant and require consideration."
ACH = Air changes per hour.
Calculate this my multiplying HxWxD for the room in metres to give m3.
Measure airflow of extract vent in m/second.
Multiply by Vent HxW in metres to give m3 per second.
Multiply that by 3600 to give m3 per hour.
Divide flow volume by room volume to give ACH.
You can find more information about working safely in our learning zone.
Unfortunately, this source does not consider Positive Air Pressure, neither for Flow Rate Nor for Dust Control.
This certainly need some interpretation.
Will comeback for recalculations.

[Pere Casals]

As you see, with a low flow and adjusting the input/output flow directions we sweep very well over the trays:

https://c2.staticflickr.com/2/1952/44481860214_7198644dbd_h.jpg

https://c2.staticflickr.com/2/1958/30264316377_70b05dd800_h.jpg

https://c2.staticflickr.com/2/1970/45203453631_542a3cca67_h.jpg

[Pere Casals]

but let me insist in the Behike test...

Just we smoke a bit the Cohiba to obtain nice "smoke threads" floating static in the air, when we start the fans we have to see how the "smoke threads" (specially those on the trays) go to the outlet smoothly, showing that fluid on the areas emiting fumes go to the outlet without mixing in the rest of the darkroom. This is the ideal situation, with a moderate flow we keep fumes far from us.

If we don't get this then we'll need a large flow and anyway we'll be in contact (more or less) with the fumes.

[Drew Wiley]

No generic figure can be given for the number of "air changes" needed. It depends on what you are specifically doing as well as the overall efficiency of your exhaust system. If you work with color chem or certain kinds of alt chemistry, you probably need at least the capacity for more air exchange than for ordinary black and white work. For mixing noxious stuff I supplement my big fume hood with a mini fume hood on a flexible hose connected to a booster fan which feeds into the main system. It is noisy, so I only use it only briefly on demand. I also have a secondary hood over a drum processor, likewise feeding into the main duct. But most color work I run in a separate portable drum processor outdoors, because I'm slightly allergic to RA4 fumes. The inline Panasonic Whisperlite fan which I use for my bathrooms in the house rather than darkroom is 440 CFM, extremely quiet, and is mounted in the attic, roof-ducted, rather than on an outdoor wall. Highly recommended. You
can adapt them for indoor wall mounting if needed - unsightly, but a simple box could be built around them in the darkroom.

[scheinfluger_77]

Do I understand correctly that the ft2 of the inlets should at least equal ft2 of the outlets, regardless of push or pull? How do the length of the duct runs (and their size) figure into the calculations?

[Thalmees]

As you see, ...
...

Pere, I'm unable to thank you enough for your input.
Thanks sooooo much.
Will comeback with to comment and final(hope) request after I draw a better refined design.
Best Regards.

[Fred L]

I must be the outlier here. best labs I've worked in had L traps passages so no push, but good ventilation/ exchange thru several large ducts (one of which is maneuverable to place over trays or while mixing dry chemistry). Never noticed any more dust in these darkrooms either. tbh, I really dislike doors in darkrooms ;)

[jp]

My experience in moving air is to keep computers cool and clean in small datacenter environments.. Dust prevention is the same goal for the darkroom. Positive pressure is good if you filter the air being forced in. Clean air leaking out the door frames or other leaky places is better than drawing in dusty air from other places. We had an economizer bringing in outside air. I used quality hepa furnace filters to keep it clean, then it was positive pressure from the air handlers to move it to it's destination. When that wasn't needed, the filters cleaned the circulated air conditioning.

In a darkroom, find a readily available size of hepa furnace filter and put it over your intake air. You'll lose a little flow, but it will be clean fresh air. Make a box around it, and slide in new filters when needed.

I have the same Honeywell hepa air cleaner in my darkroom. It keeps my negatives drying dust free. I would like to add fresh air at some point as it heats up in the summer while I work in there and gets cool in the winter. Most likely I'll use a Panasonic bathroom fan and build a light tight box for the air path.

[Drew Wiley]

While home air cleaners can be helpful is many situations, there is a big difference between something containing a so-called HEPA filter and a true HEPA system. Most items marketed as HEPA do not even begin to meet the EPA definition of that term, let alone more stringent EU requirements. I call it the BS coefficient. HEPA furnace filters are another example of abuse of the terminology, though they obviously have legitimate applications. I sold millions of dollars worth of true HEPA equipment over the last decade, prior to retirement, related to potential control of actual toxic dusts. There are all kinds of devices out there that are not properly rim-sealed regardless of what the filter itself is. Stuff gets around the filter. Fortunately, in most darkroom situations the intake vents merely need to filter out dust to a minor degree. If you need true HEPA intake air, maybe you should move! I can sympathize with anyone with pollen allergies, etc., but those are fairly large particles. Why do I even bring up this kind of seemingly nitpicky distinction? Well, it can make a big difference if you are planning to experiment with a photographic process requiring toxic powders like chromium salts that you don't want accidentally dispersed, or need to clean up after an accidental spill. I've met quite a few artists who have serious long-term health effects from that kind of scenario. Otherwise, for garden variety black-and-white printing, a certain amount of compromise in fuss and economy is generally OK.

[Pere Casals]

so-called HEPA filter and a true HEPA system.

HEPA flters range from E10 to U17, all are true norm EN 1822:2009 HEPA filters. Performance depends on the specified grade...

HEPA filters, as defined by the United States Department of Energy (DOE) are H13 in the European Union. See Specification section here:

https://en.wikipedia.org/wiki/HEPA

Those that are used by lots of people suffering allergies (pollen, acari) are an overkill for a drakroom. For example my cheap Honeywell 16000 is H13.

[Luis-F-S]

Just don't go crazy with it and don't loose any sleep over it.
L

From post #9............you may want to disregard a lot of the next 40 posts.
L

[Drew Wiley]

Luis - these threads get perused for all kinds of reasons besides the original question. So a bit of info overkill might be of real benefit to certain people. For example, in some parts of the country, a darkroom might well be constructed in a basement with radon issues. There are basic timed, automated easy-install fan systems from these same manufacturers designed to address that specific problem. In urban areas like around here, darkrooms and other craft spaces are often put in old industrial or military buildings with serious hazmat issues. Some of these involves rental spaces where a neighbor might be carelessly spraying something hazardous. The average photographer or artist tends to be very naive about these risks.
You can personally do everything right yet be affected by something else nearby. Less than a year ago, I attended the funeral of a friend who died at 34 due to merely living adjacent to something like that, and there was another friend not long before. Several others are terribly ill due to being exposed to substances in those kinds of buildings. I've seen people with hair falling out and all kinds of wierd cancers, kidney failure, you name it. Don't assume anything... And Pere, you seem to rely a lot on generic Wicki information. I have an actual EPA Instructors license related to hazmat. I haven't renewed it because I'm retired now, and it's expensive to do so. I'm not guessing about any of this. I've worked directly with the German engineers in charge of designing the proper kinds of extraction equipment that is now sold worldwide. And EU standards are in fact way more stringent than those in the US. If you want to learn about it, there are Govt manuals as thick as a phone book - quite different from a brief Wiki paragraph. But your description of smoke studies in confined spaces is certainly helpful. That also applies to getting properly fitted with a respirator when basic room control itself is not adequate. They are tested in small smoke chambers. Due to all the tech industry around here, there are a number of businesses entirely dedicated to industrial safety as well as cleanroom supplies. For others, I recommend LSS (Lab Safety Supply) as a web or phone order source - huge selection of not only safety gear but also all kinds of lab items useful to any serious darkroom.

[Pere Casals]

And Pere, you seem to rely a lot on generic Wicki information.

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.

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...

[Tin Can]

I wish at least one of our 'experts' would document sources with hyperlinks (https://blogs.msdn.microsoft.com/xweb/2010/04/26/different-types-of-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.

[Drew Wiley]

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.

[Drew Wiley]

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.

[Pere Casals]

Desktop air purifiers are not true HEPA.

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"

[Jac@stafford.net]

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.

My wife has had COPD since childhood. We run two separate room HEPA filter devices (https://www.walmart.com/ip/Honeywell-QuietCare-True-HEPA-Air-Purifier-17000-S-White/870795?athcpid=870795&athpgid=athenaItemPage&athcgid=null&athznid=PWVUB&athieid=v0&athstid=CS020&athguid=466001f5-46cfa622-379841f99a18a716&athena=true) 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?"

[Pere Casals]

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.

[Jac@stafford.net]

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!

[Pere Casals]

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.

[Drew Wiley]

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.

[Jac@stafford.net]

Pere - False. "Industry standards" do not equate with EPA or EU specs which account for how the entire SYSTEM is sealed.

Your postings target extremes which we will never experience in our darkrooms.
Back to your bubble, boy.

[Pere Casals]

Pere - False. "Industry standards" do not equate with EPA or EU specs which account for how the entire SYSTEM is sealed.

hmmmm, Drew, please see this HEPA manual: https://www.honeywellstore.com/store/images/pdf/hpa-300-air-purifier-manual.pdf

In this case, Honeywell says:

THE DOCTOR’S CHOICE
TRUE HEPA
ALLERGEN REMOVER
AIR PURIFIERS


If they are lying then somebody suffering severe asthma can die. This would be very expensive for a company....

Do you think they are lying ?

My bet is that they fulfill EU HEPA H13 level and US DOE HEPA specs.

HEPA ratings regulate filters, sealed systems are regulated by ISO 14644-1 and 14698 or by US FED STD 209E that's a bit obsolete but still in wide usage.

[Drew Wiley]

Bingo. Not an item there is remotely HEPA by EPA spec. I'm not implying those kinds of cheap devices are not useful in darkroom spaces or for home dust control, and I do know a thing or two about allergies. I had life-threatening allergies as a child, and my wife works in an allergy clinic. I use an even cheaper portable filter for the intake air on my film dryer cabinet; but it's in a room quite clean to begin with. But you plainly do not have a clue what you are talking about, Pere. I am making a distinction quite important for those who might opt someday to work with HAZARDOUS metal salts in alt processes, or who are thinking about leasing a darkroom space in a converted industrial building possibly having toxic compounds in walls or in use in adjacent studios, or toxic mold situations possible in semi-tropic environments. That could potentially include quite a number of photographers dreaming about being able to do their own printing. Some of the art collectives in this general area have proven themselves to be downright deadly, i.e., fatal. Painters, photographers, and sculptors take out leases on those spaces without understanding the risks. And those risks can be extreme. Not everyone has space in their home per se. Some alt processes use highly flammable solvents, or they might be in use by someone else in a craft studio nearby. All it takes is a single spark from a non-registered air extraction device or ungrounded duct line (that has to be factored in too, in the design of legal equipment, or even in common-sense fume hood ducting; even an ordinary clothes dryer duct hose requires it). Many others of us need not worry about such technicalities, and nitrile gloves and a simple ventilation system might be enough. But you need to know how to ask the right questions first. Don't assume.

[scheinfluger_77]

Ugh! Can we just get back to darkroom ventilation solutions?

[Pere Casals]

Drew, let me add that HEPA qualitification was issued for the Manhattan project, A-Bomb, so to arrest radiactive particles. I guess because of that it was regulated by US Dep of Energy (nuclear section). Initial meaning was "high-efficiency particulate absorber", later a bit changed.


"The original HEPA filter was designed in the 1940s and was used in the Manhattan Project to prevent the spread of airborne radioactive contaminants. It was commercialized in the 1950s, and the original term became a registered trademark and later a generic term for highly efficient filters"

But "true HEPA" in the USA is H13 HEPA in the EU.



Ugh! Can we just get back to darkroom ventilation solutions?

IMHO we ended that debate yet, http://www.largeformatphotography.info/forum/showthread.php?148407-Darkroom-Exhaust-Fan(400-CFM)-For-Positive-Pressure-Plus-DR-Design&p=1464123&viewfull=1#post1464123

but if you have something to add, please don't hesitate...

[Drew Wiley]

This IS about ventilation solutions!! Is your fume duct grounded or otherwise static-resistant? Does your intake air need HEPA filtration due to adjacent atmospheric conditions otherwise beyond your control? - which might include pesticides in farm
communities, and not just urban hazmat issues. Do you work with hazardous powders? Not every darkroom is limited to Dektol and D76. I can think of at least thirty "artistes" in this immediate area who were alive two years ago, but are not today, simply because they did not ask such questions in advance. Or maybe someone might like to build in extra features right from the start, when it is easiest to remodel, just in case they want to step up to color printing or alt processes, or even mix their own pyro from powder instead of buying it liquid A&B like me. I've got all kinds of nasty chem in my lab for specialized incidental rather than daily purposes that I'd hate to spill. ... But gosh, Pere, I'm tired of talking about it to you. Just turn in your job application at the one of the Fed Rad Labs here - either Lawrence Berkeley or Lawrence Livermore. I'm sure they'll be quite impressed. They use water-filtered vacs, of course, not HEPA. But you already knew that.

[Pere Casals]

Does your intake air need HEPA filtration due to adjacent atmospheric conditions otherwise beyond your control?

It depends on if one likes dealing with dust or not !!!

[interneg]

In the simplest terms: if you want to work safely in the longer-than-very-short-term with dichromates or much of the wetplate chemistry, you should not be doing so without appropriate (ie chem lab standard) ventilation, especially if you're working in close proximity to other people, animals etc.

A cleanroom would be most useful for dealing with any cold mount processes - they are a magnet for dust!

[Steven Ruttenberg]

I would like to have my darkroom with positive pressure that is filtered air being pulled in from my house. Due to where my water lines are for where my sink will go, I may need to have a vent hood that has a separate fan/filter that draws the air over the sink and vents to the outside. I may install a separate filtered vent with a valve that allows the incoming air from house to vent out when the vent hood over the sink is not on, while maintaining a small positive pressure to keep out the dust. In essence, like a big version of a table top clean room. I think the only thing I would want is explosion proof fans if they are not too expensive. Will also need to have a vent line that is filtered to the outside for the enlarger/s.

I am keeping this simple, but at the same time, I want to keep any chemical vapors I vent to the outside to a minimum (no need to add to the pollution if I don't have too. Not that the amount or type I would be venting is that harmful)

[Drew Wiley]

You could supplement a serious fume hood fan with a simple low-pressure automated "attic fan" if necessary, which would allow for modest exhaust even when you're not there. For the latter, a simple dryer duct flap hood on an outside wall would work in lieu of a fancy valve. The ideal configuration with a sink allows air to be drawn past you over the sink, then up into the hood. I periodically tweak my own system, which began with a bunch of big components salvaged free from local industrial lab renovations. Doing it "perfectly" from the start would have been way beyond my budget.

[Drew Wiley]

Guess there are some people that can't appreciate true cleanroom standards in a personal darkroom. Maybe they enjoy endless spotting; I dunno. A true HEPA "system" traps all the air via tight gasketing and conveys it through the filter, both preventing any other route of airflow which might either damage the motor or might allow fine dust any alternate path out. This also makes a real difference, as someone already noted, at the mounting station. Permanent cold mount foils, now routinely used for color prints, are extremely unforgiving. If dust gets stuck there, that's it. Then when one is doing even ordinary framing using acrylic, which is quite electrostatic, any dust or lint around the room is going to spell a serious headache if it gets trapped behind, and you have to take the whole frame apart to remove the "fish" (the term used by pro framers) from within the fishbowl. So I don't know what Jac means by "our darkrooms". But it doesn't sound like any kind of darkroom I'd want. Those of us who once did a lot of big Ciba prints know what kind of hell its own electrostatic properties
were capable of. Working clean was not an option; you either did it or went both broke and insane.

[Luis-F-S]

Thanks so much Luis. It is of great help.
Let me please try to understand what you mean exactly.

There are four(4) fans, only, No louvres.
Two(2) Fans are fit on the door for Positive Pressure(intake). The other two(2) are on the other side of the same wall, for exhaust(draw air out). No passive louvres.
If I understand you correctly, you mean to take one Positive Pressure Fan from its sealed place in the door, leaving only the opening, beside the other working Positive Pressure Fan.
My apologies Luis if my understanding is not correct.
I think that will disturbs the Air Pressure Gradient. Plus, some light will leak from the corridor to the darkroom.
The same case for Positive Pressure Gradation, even if I replaced the Positive Pressure Fan, with a light tight passive louvre.
.

What actually happen, is connecting each two(2) fans in each area, to an extension power cable with individual "On/Off" switches. If I need two(2) fans to work together, will use the main switch, if I need only one(1) to work, will use the individual switch.
.

I may settle on this solution.
But before that, I wish I can validate my primary design(or any better alternative) through this thread.
Until now, I do not know if inverting exhaust fans(to work as Positive Air Pressure), is appropriate or just arbitrary experimental?
Appreciate your input.
Regards.
Doran fans have 2 louvers to make light tight. If you remove one it doubles the fan output.
Read the instructions on the fan.

[Drew Wiley]

Those Doran light traps aren't perfect. Their intake vents are best installed on the side of a building normally shaded, or else mount a simple shade above them. Set them in with dark adhesive caulking, not clear. Same goes for fans. Another reason I prefer an exterior mounted fan with a long indirect duct.

[Jac@stafford.net]

So I don't know what Jac means by "our darkrooms". But it doesn't sound like any kind of darkroom I'd want.

Just curious - do you wear long sleeves, a hair net (even if no hair), face mask and cotton gloves in your ideal darkroom?

[Leszek Vogt]

There are many ways to do this. Not really understanding the layout....I could offer this...

**Fans by Fulltech Electric (sold by Jameco) 226 CFM each (120V) - they force air out
**The sketch is an overkill on light tightness (loosely based on Chris's idea)
**If the window is sliding then it could be installed and part blocked with plywood piece

You can install more than two fans if you desire. Care must be taken to make sure critters don't have a chance to get in via the duct. Don't have the data how quiet the fans are. I have installed Broan (super quiet - not the conventional type) fans in the bathroom and they are still quiet - 10yrs later. Panasonic fans seem to be even quieter. I've stood appx 2 ft away from one and could barely hear its purrrrring. Both fans can be installed on individual switches/dimmers....or just one. Any sort of rubber type gasket (in the install) will help preventing metal to metal noise. You can also add an inline fan (depends on you) to force the air out more efficiently. Good luck.

Les

183962

[Drew Wiley]

Hi Jac. Depends on what I'm doing. For film work I swab down the entire cleanroom, ceiling to floor. The room is equipped with an industrial air cleaner and triple filtered air. I wear an all-dacron cleanroom smock, which resembles a full-length lab coat but generates no lint. Last time I bought one it was only about thirty bucks, so these are certainly reasonable for every darkroom worker who wants to reduce spotting. In my case, where multiple contact negatives or masks might be required for a single color image, every bit of dust prevention up front is worth it. 8x10 film ain't cheap. But because this particular darkroom is my smallest and easiest to keep comfortable in winter, I also do black and white printing in there, but never at the same time as color work because fiber based paper obviously generates some fibers. I have a different room where the big 8x10 enlargers are, cutting table, etc., and yet another room for mounting prints. The sink room is separate from all of this, and no, I don't wear cleanroom gear in there, just chem gloves etc. Then the shop is peripheral to all of this, but itself quite clean due to the kind of equipment I use (otherwise, I do woodworking outside under a covered porch). Having a HEPA dust extraction system saves tons of time during shop work, well worth it, though I'll admit I had an inside track acquiring it. Every single serious cabinet shop and museum shop in this area is now equipped with that sort of clean machinery, otherwise
they would no longer be competitive. Working clean equates to working efficiently, which in turns means working profitably. Certainly not every photographer is going to have this kind of gear, but the same basic cleanroom habits are applicable everywhere, even with digital printing operations, because dust removal isn't fun in that case either. I'd think one would want to be rather fussy about the topic when scanning. Hair and beard covers aren't at all unrealistic in cleanrooms; in fact, they're mandatory in industrial ones. It takes half an hour just to suit up in the pharmaceutical labs. That amount of fuss would obviously be overkill for any darkroom; but still, perusal through a cleanroom supply catalog or website can teach photographers about numerous ways to save headaches down the line. You must be of my brother's generation. He passed away, but I still remember his first professional darkroom in an old barn in Santa Barbara with the walls lined with Natl Geo maps, and that old hairdryer-looking Beseler enlarger which he bought second-hand. It doubled as a bathroom. That old building probably sold for several million bucks later on, given its proximity to the beach. He did well in photography for awhile, and then got tempted to become a local realtor himself. But he'd farm out color printing to me.

[Duolab123]

My biggest source of contamination is ME. I sometimes think I am shedding more than my cats. I leave any street shirts out of the darkroom while I'm printing. I wear a clear t shirt and a cap. And then I'm very careful. Who ever is in charge at Ilford, get rid of the static black plastic bags, maybe Lead would work :-) . I still have some of the nice old Kodak 3 ply bags, craft paper on the outside, with plastic /metal foil laminate on the inside.
I got my hands on one of the old Kodak 5kV static eliminators with a camel hair brush. Boy that gets rid of static on plastic. It's a bit intimidating, turn it on and it's humming, you can smell, Ozone??? Dust is a pain.

[Luis-F-S]

Those Doran light traps aren't perfect. Their intake vents are best installed on the side of a building normally shaded, or else mount a simple shade above them. Set them in with dark adhesive caulking, not clear. Same goes for fans. Another reason I prefer an exterior mounted fan with a long indirect duct.

If you would read the OP's posts, he said that the intake and exhaust are located on the same wall in an interior corridor. Mine exhaust to an exterior wall and I've never had an issue with the factory louvers. Doran fans have a double louver to make light tight enough (though maybe not for Drew), you can often remove one of the louvers and double the flow. It might be better if you fur down and build a plenum over door to extend the full 4.5 m length of the wall; put an A/C register with an air filter for the intake of the plenum and then install the fans on the plenum. You should paint the inside of the plenum black. You could then center the fans a little better on the plenum rather than on the same wall as the exhaust.

You can look at how I did the exhaust in my darkroom to get ideas, except I used it on the exhaust and you would do the same on the intake. L

[Drew Wiley]

Intake and exhaust vents in proximity is counterproductive - risks drawing the fumes right back in.