The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Acidic Atmosphere in Our Anodizing Department

We have a 700 s.f. anodizing shop, well ventilated, with about 5 active tanks. We are noticing acidic (pH 4-6) atmospheric conditions in the work areas. We believe that it may be coming from the Direct Fired Heater in our air makeup unit. Has anyone else had this problem?

Eric Jones
Project Manager - Boise, Idaho, USA
2003

---

Well vented or not, I'll give ten to one that it's the anodizing tanks not the heater.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

Or the deox/desmut tank. It is extremely difficult to capture 100% of the vapors off of the anodizing tank. Sometimes the first rinse tank will get to a pH of 1-2, so that might be a source also. What about drips?

James Watts
- Navarre, Florida
2003

---

10-1, eh Ted? How much $$ do you have? (We identified the heater as the cause) This heater is on our make-up air unit (26,000 cfm), its winter, here in Idaho, and the combination of the moisture in the air, going through the gases from the gas burner (not stacked), created an acid rain effect. It was severe enough to cause slight pitting in our exposed aluminum parts, and turned our ph paper to a pink/red color overnight. (its amazing that no noticeable odor was present). We shut the heater down for a night (but not the blower), and the ph paper showed no change. We learned a lesson here.. that may help someone else out in the future.

Marc Green
anodizer - Boise, Idaho
2003

---

2003

I've been wrong many times before and will be again, Mark. And I appreciate that reactions between water and organics can cause an acid condition--as is often seen in the solvent reservoirs of vapor degreasers. But I can't concede to things that are contrary to a lifetime of experience until the evidence gets reasonably compelling. I've been to very few anodizing and plating shops where the atmosphere isn't corrosive, ventilation or no, space heaters or no. But I can't recall any instance of a home, commercial installation, or industrial facility which did not use acid yet had a corrosive environment.

I am absolutely not saying you are wrong. You have presented enough evidence that I very much appreciate the feedback, and will keep it in the memory banks for the future. But I honestly can't concede 'case closed' based on one instance and one test; winds shift and I have seen the acid plumes from exhaust stacks sucked back into a building one day and not the next.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

---

First of two simultaneous responses --

Eric,

Excuse me putting my oar in .... but are you sure that your 'good' ventilating system isn't plugged up or misbehaving?

I have encountered this more than one time! Stack iced up (but that was in winter time at Sel Rex in Ontario), scrubber plugged up in Vancouver due to new owner never using the wash-down sprays.

Anyhow, it's a thought! ttfn

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).
2004

---

Second of two simultaneous responses --

We followed this up by leaving the heater on one more time, and again, the ph paper showed color change. Our tanks are left covered every night before we go home for the day. Most home heaters are properly stacked to allow the gases (carbon monoxide, nitrogen dioxide) to escape, and not be pumped into the home. Our blower lacks such a stack. Our blower sits at ground level, while our exhaust fans are atop our 35 ft roof downwind of the blower). I installed carbon monoxide detectors as soon as we installed the blower (and I was informed that gasses werent stacked) I've had peak level of 40 ppm (this was only one time) in the anodizing dept. I've worked in this business for long enough to recognize an acidic smelling environment (although I am probably de-sensitized), but weve had countless people in here who have said they smell nothing out of the ordinary. We are doing some in-depth air quality testing this week, I'll keep everyone posted. In the meantime..if anyone else has any other suggestions/probabilities of what may be causing our issue, I'd love to hear from them! All I know is that heater on= pink ph paper...heater off=no change.

Marc Green
anodizer - Boise, Idaho
2004

---

I believe that you can make some acid in a heater flame if there are chlorohydrocarbons in the burner air. Like HCl, for example. Do you have any degreasers or using some solvents in your shop? Can you test for chlorides?

  
Tom Pullizzi
Falls Township, Pennsylvania
2004

---

2004

Just an update here. We had some air samplers running in our dept for an 8 hour shift. We tested for HNO3, H2S04, and HF, with the blower operating (so I don't think we are sucking in our exhaust from the ano line) The results showed that we were way below the threshold for exposure over an 8 hour day. However, these tests did not/could not show what the actual ph of the air was that we are breathing. We have discontinued using the make-up air unit untill we resolve this problem...we have left ph strips out, and since shutting off the make-up air unit, and the heater that works with it, we have seen no color change on the litmus paper. In answer to your question, Tom...no we do not use any solvent degreasers in the shop. The only solvent we regulary use is acetone ⇦ this on eBay or Amazon [affil links] Warning! highly Flammable! . As far as chlorides go, the only one we use would be HCL, and thats only during some testing that we do on our anodic coatings (in very small quantities) Is anyone aware of any test method that can be done to determine the acidity of the air (other than the crude ph paper)? Our labs are not aware of any such test. Also, does anyone know what the threshold is for breathing possible acidic air over an 8 hour period? I'm still holding tight to my "acid rain" theory, I just need a way to prove/disprove it.

Marc Green
anodizer - Boise, Idaho
(anodizer extraordinaire)

---

Good afternoon:

The OSHA website lists permissible exposure limits (PEL) based on an 8 hour time weighted average for several common mineral acids. Go to- http://www.osha.gov/SLTC/pel/index.html I think the info you're looking for is in Table Z1 and Z2 on this web page. Hope this is what you're looking for. And I hope you don't have to spend big $ for industrial hygiene testing.

Steve Bizub
- St Louis, Missouri
2004

Mark,

You said that your blower is at ground level and that your exhaust fans are on the roof, 35 feet up.

So my question is ... how high are the exhaust fan stacks? They should be at least 7 feet, presupposing there are no other and higher buildings nearby. Otherwise the roof eddy zone effect could cause some of the fumes to waft downwards. Anyhow, food for thought ... and my regards to your dawg.

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).
2004

---

2004

We had air monitoring done in 2001 for an 8 hour period.

Limits were

1.0 mg/m3 permissible for Sulfuric
2.0 mg/ m3 permissible for Nitric
2.0 mg/m3 permissible for Sodium Hydroxide

My operators tested at 0.13 mg/m3 for Sulfuric None detected for Nitric 0.032 mg/m3 for Sodium Hydroxide

I run an etch recovery system and the caustic fumes can be pretty intense at times with the little exhausting we have that is why I had the testing completed. I hope this helps a little.

Bruce Pfaff
- Wausau, WI