Since you're referencing an SDS, I'm assuming your talking about the occupational environment, in which case it makes sense to talk about occupational exposure limits. The American Conference of Governmental Industrial Hygienists (ACGIH) has established non-enforceable Threshold Limit Values (TLVs) for different oxidation states of Chromium:
- Chromium VI - 0.0002 mg/m3
- Chromium III - 0.003 mg/m3
- Chromium metal - 0.5 mg/m3
These values refer to the maximum recommended 8-hour time weighted average exposure concentration for a given substance. A lower number means someone is allowed less exposure; a higher number means someone is allowed a greater amount of exposure.
Depending on your product and process, it may make sense to look at measuring exposure to each of the different oxidation states. Particularly for chromium VI, because the exposure limit is so low, it's doesn't take much to overexpose someone.
Note also that if you're in the US, OSHA has a limit for Chromium VI of 0.005 mg/m3. If you exceed this limit, there are a ton of requirements that kick in. See 29 CFR 1910.1026 for more information.