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Does chromate conversion coating generate hex chrome fumes?

Can anyone tell me if the process of chrome conversion of aluminum parts using a chromic acid solution (Unichrome/ Alodine) without heat or electricity will generate hexavalent chrome vapors (emissions)? Considerable or negligible emissions? Batches are typically small; <2 gallon dip tank used intermittently.

Larry Neenan
- Yorba Linda, California
2003

Hi, Larry. The same question was asked and partially answered as letter 21821. I say "partially answered" because more definitive input would certainly be appreciated, folks!

Your having to worry about a less than 2 gallon occasionally used chromate conversion tank while the platers' lobbyists are still fighting emission standards for hard chrome plating tanks after 74 years of known hazard is a bit ludicrous. It's like trying to write a history of maritime disaster by lumping together the sinking of the Titanic and a fellow getting his feet wet when his rowboat leaked. There seems to be a lack of perspective on both sides. Somebody please show me a personnel exposure badge that registered ANY chrome exposure from a 2 gallon room temperature chromate conversion tank and I'll certainly change my tune--but I think I'll have a long wait :-)

Meanwhile, though, OSHA says all tanks containing Class A chemicals (like chromic acid) in ANY concentration must be ventilated; I don't even see how the rinse tanks can be unventilated if OSHA rules are followed because "any" can be an infinitely small amount. So the answer is, negligible emissions or not, you have to ventilate it. Good luck.

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

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So Ted....let me get this right. You're an operator working over an air agitated (typical), unvented (not typical) chromate conversion tank chromating aluminum parts for.. lets say...2 hours total (exposure time)/day. And, for the sake of argument.. we'll make it a small tank.. 250 gallons or so. Would you not want to wear a respirator, apron, gloves...etc.?

Marc Green
anodizer - Boise, Idaho
2003

Marc, if I were an operator I would wear rubber gloves ⇦this on eBay or Amazon [affil links] and apron ⇦this on eBay or Amazon [affil links] and goggles ⇦this on eBay or Amazon [affil links] even when the boss wasn't looking. I feel that all chrome plating tanks should be ventilated (some aren't), but I admit to being neutral about ventilating chromate conversion tanks. If a regulator reads the rules as requiring it, I don't get hot; if a shop owner doesn't read them that way and chooses to abate other problems first, I appreciate that too. But my opinion is only that anyway, and Larry's tank has to be ventilated by OSHA rules regardless of what he or I think.

Larry's tank is not 33 oz/gal+ as in chrome plating, but what, 1 oz/gal? The temperature is not 130+ °F as in hard chrome plating, but ambient. There is no electricity generating hydrogen and forming troublesome mists. You just called a 250-gallon tank 'small', and Larry's tank is more than a hundred times smaller than what you call "a small tank"! And he uses it only intermittently. So I'll stand by my analogy that he's got a rowboat with a slow leak while ocean liners are at Mayday.

The longest I ever wore a respirator was 3 or 4 hours of misery. I would not voluntarily wear one while doing chromate conversion coating until someone shows me a personnel exposure badge which demonstrates that chromate tanks represent an actual exposure hazard rather than simply the regulators' next step in trying to keep busy after the serious chromic acid exposure problems have been solved. Again, I'm not sure there is utterly no inhalation hazard, as mentioned in the previously referenced thread -- I'm just reasonably confident.

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

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2003

Ted,

I agree that Larry should have no worries. From my personal experience, however, in working around a relatively small conversion tank, 150 gal (only 2-3 oz/gal, ambient temp) that was air agitated . . . there was a noticeable fuming going on.. approx. 6" layer above the solution level. The odor, albeit not choking, was also definitely present. The mixture we used to use was in powder form, and when one opened that drum, respirators were mandatory, as those fumes would asphyxiate a person. We have since eliminated all hex-chrome solutions from our line, so I can't get any data on exposure. I will say though.. that we all had to wear air samplers for an 8 hour shift some years ago.. and all results came back negative (although.. no-one was doing any chromating that day). But, to make a point..I'm sure, that there were a lot of asbestos workers, and lead burners that would now (or, before they died) give their left...ummm (anatomy part edited) to have had a respirator, even though no "hard data" was available.

Marc Green
anodizer - Boise, Idaho

I'm not demanding hard data if there is none, Marc. My soft data is simply that I haven't seen the severe staining or smelled anything like what a chrome plating tank smells like, and calculate that we are dealing with emissions at least a hundred times lower than the emissions from chrome plating tanks (that people are still resisting ventilating). If you see a visible or choking fuming, yes, it needs ventilation.

Making up a tank is something totally different, and I would never shovel chemicals from a drum without wearing a respirator. But I wouldn't even hand sand virgin wood without a respirator. Powdered anything doesn't belong in our lungs -- not powdered sugar, not nuthin.

But I don't accept the "better-safe-than-sorry" asbestos and lead analogy because I'm not at all sure that the "just-wear-a-respirator" alternative is actually safe. I have C.O.P.D. and find respirators very uncomfortable to breathe through, and hard work on the lungs. I know some shops where operators wear respirators all day every day, and I am not willing to concede that prolonged, continuous all-day use is harmless. Is there any data demonstrating that it is? Hopefully someone will point me to such data. Thanks for your input, Marc.

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

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Ed. note: we note that this posting is from 2003; some years have passed and I can't say whether anyone is still resisting ventilating chrome plating tanks, especially with the current environmental pressures against using PFOS fume suppressants as an alternative.