In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Among applicators with usage information sufficient to evaluate exposure - response patterns , we used Poisson regression to estimate adjusted rate ratios ( RRs ) and 95 % CI for cancer sites with > 10 exposed cases for both lifetime ( LT ) exposure days and intensity - weighted ( IW ) lifetime exposure days ( accounting for factors impacting exposure ) .
### Output Text:
Among applicators with usage information sufficient to evaluate exposure - response patterns , we used Poisson regression to estimate adjusted rate ratios ( RRs ) and 95 % CI for cancer sites with > 10 exposed cases for both lifetime ( LT ) exposure days and intensity - weighted ( IW ) lifetime exposure days ( accounting for factors impacting exposure ) . 