Attempting to better understand Hexavalent Chromium genesis

[Learjetz]

Hexavalent Chromium(Cr+6) is known to be found in dyes, pigments, paints as a solid and is often also discussed as a gas when doing "hot work" on stainless steel metal. Ventilation seems to be a very important tool to mitigate exposure to this harmful chemical.

I am seeking knowledge to help better understand how this element leaves stainless steel during "hot work." What are the circumstances that you should expect to create it as a gas. If you are creating Cr+6 as a gas, is it also being deposited as a solid on the material you are working with? If stainless steel is being welded, are there any solid deposits left behind on the metal surface that is creating the Cr+6 gas? In all the safety discussions I have read about Cr+6, the vast majority talks about proper ventilation which has led me to believe that it is not created in a solid form during this process. I am left to assume it sublimates from the steel.

Should one also expect to create Cr+6 during laser engraving of stainless steel?

Is there a possibility it could be created during a home oven cleaning cycle?

Thank you

 

[trurle]

To my experience, chromium is not emitted from stainless steel as ion at +6 (as chromium trioxide) if hot-worked. What i actually observed was the black or slightly greenish deposits of chromium and oxide mixes (oxidation state 0, +2 or +3). These become a nuisance in doping/deposition oven from +850C, making observation windows non-transparent.

Generation of hexavalent chromium oxide by laser cutters...possible, although yield likely to be low. After all, hexavalent chromium oxide decompose to trivalent at 200C. Some generation of hexavalent chromium could happen due to rapid quenching of adiabatically expanding fumes if impulse laser cutting is utilized.

Of course, exposure to hot work gases may (and usually would) cause a generic metal fume fever. Take care.

 

[Learjetz]

This video talks about the necessity to filter Cr+6 from welding fumes.

My assumption is that because there is so much emphasis on extraction of fumes to reduce Cr+6 exposure, there must not be any exposure through solids on the surfaces of the workplace. My lack of understanding brings zero confidence in my assumption, unfortunately.

 

[trurle]

This video talks about the necessity to filter Cr+6 from welding fumes.

My assumption is that because there is so much emphasis on extraction of fumes to reduce Cr+6 exposure, there must not be any exposure through solids on the surfaces of the workplace. My lack of understanding brings zero confidence in my assumption, unfortunately.

Cr+6 would be typically produced as fine airborne dust. Of course, it can contaminate work surfaces, although only mobile particles are of concern. OSHA regulation 1010.1026 specifically limited to "dusts, fumes, or mists". Brushing and suction fans would be adequate to handle a hazard.
Here is the citation from regulation

Cleaning methods.
1910.1026(j)(2)(i)
The employer shall ensure that surfaces contaminated with chromium (VI) are cleaned by HEPA-filter vacuuming or other methods that minimize the likelihood of exposure to chromium (VI).
1910.1026(j)(2)(ii)
Dry shoveling, dry sweeping, and dry brushing may be used only where HEPA-filtered vacuuming or other methods that minimize the likelihood of exposure to chromium (VI) have been tried and found not to be effective.
1910.1026(j)(2)(iii)
The employer shall not allow compressed air to be used to remove chromium (VI) from any surface unless:
1910.1026(j)(2)(iii)(A)
The compressed air is used in conjunction with a ventilation system designed to capture the dust cloud created by the compressed air; or
1910.1026(j)(2)(iii)(B)
No alternative method is feasible.