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: The catheterization procedure is safe , with no immediate complication in 111 infusions of BCNU .
### Output Text:
The catheterization procedure is safe , with no immediate complication in 111 infusions of <span class="chemical">BCNU</span> . 