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How to calculate hex chrome air emissions from a tank

January 19, 2009


I have been struggling to find a formula to calculate air emissions of hexavalent chromium from my finish room operation. I want to make sure our company is below the allowed state standard that requires a permit to release toxic air pollutants. I can't find anything or anyone that would help me.

Here is my situation: I have a Iridite 14-2 chromate tank. The contents of the tank is:
40 gal of water and 5 lbs or Iridite (which is 0.6 lbs or sodium silicofluoride, 0.4 lbs of ferricyanide, 1 lb of barium nitrate, and 3 lbs of Chromic Acid, from MSDS).

I know the surface area of the tank, the velocity of the local exhaust ventilation system (so, I have my cfm), the temperature of the tank is 100 F, and the vapor pressure of water at that temperature is 49.18mmHg. However, since the Iridite 14-2 is a powder, I can't get the vapor pressure for it. So, does anybody knows a formula for me to calculate to the best of engineering capabilities, what would my emissions would be? I want to use this to figure out if I need to stack test or not? By the way, there is no controls such as mist eliminator or scrubber.

Any help would be appreciated.


Sergio Macieira
EHS Coordinator - Wilson, NC, US

January 19, 2009


If you want to make certain that your company is below threshholds, do not rely solely on your calculations, but rather supplement them with actual sampling at the tank.

Willie Alexander
- Colorado Springs, Colorado

January 20, 2009


Several things I would like to point out:

1. The information on the MSDS is probably not an exact number (otherwise you would have most of a formulation) but rather a series of "less than" amounts
2. 100 °F. sounds rather high to be running Iridite 14-2 at. Check the manufacturers information. I remember a range of 65 to 100 deg F. with the best range considered to be 70 to 80 deg F.
3. If you have an exhaust, the calculations should have been done when the exhaust was designed. This is presuming that it was engineered not just guessed at.
4. Since you are concerned with workplace exposure, as the last reply stated, check it. You can order worker exposure sensors from some testing labs which allow you to ship them back for evaluation. If you have a "typical" worker in the area wear the testing "badge" you are allowed to use that data a typical for all workers in the area. This is the means to comply with regulation for worker exposure. Calculating air emissions just gives you an amount that is theoretical.
5. With the process you are using and the exhaust I would guess that worker exposure is not a problem. It does give one piece of mind to have the document from the testing lab when an inspector comes in.

Gene Packman
process supplier - Great Neck, New York

January 22, 2009

Once, at the insistence of some inspector, I did some rudimentary air monitoring, using a Draeger tube, of the air in the 'breathing zone' next to a vigourously air agitated yellow chromate tank. The test came up dead negative.

However, this was in the past. There's a new OSHA standard for hexavalent chromium limiting it to 1 microgram/cubic meter of air. This is far too low to see with any test you can do yourself, and must be run by a contract lab that has a properly configured ion chromatograph. Not a cheap test, but if you want absolute security from citations and lawsuits, perhaps you should spring for it.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

January 26, 2009

Thanks for the responses. But so far, nothing on calculation air emissions. I hope someone will show up to help me.

Sergio Macieira
- Wilson, NC

January 27, 2009

Sorry, but there are so many variables and so little positive information for each variable that it is impossible to do a valid calculation. Testing is the only answer.

James Watts
- Navarre, Florida

January 28, 2009


1)I cut the bottom off a one gallon plastic distilled water jug so that the cut off piece was about one inch tall and six inches by six inches square. I put a horizontal 1/4 inch diameter glass rod about 6 inches above this "tray." Then I draped over 5 inch wide filter paper which went to the bottom of the tray (both ends in the tray). Next I put about 1/2 inch deep distilled water into the tray. I put this apparatus in the back of a fume hood in a chemistry lab. As the air passed over the filter paper the water evaporated and more water was sucked up by the paper. After a time a distinctive horizontal yellow line of hex chrome appeared near the glass tube. This happened with the 0.1% hex chrome water spolution that was at 55 deg. C. Thus a qualitative test for hex chrome.

2)I sucked air through a water trap three feet above the 0.1 hex chrome beaker and at 97 deg. C and detected 0.023 mg/cu.m of hex chrome.


Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA

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