Hydrogen Sulfide Modeling in Sewergems

Dear Folks , 

I have run a model with Hydrogen sulfide analysis , after made the analysis i got the result for H2s in and out concentration  , my question is : do we have a limit for H2S concentration in sewer pipe line ?? or do we have a code or standard that have limits for H2S concentration  ??

is the concentration limit depend on pipe material type , and what is the limit for each pipe material ??

Thank you all