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: Experience in war / tropical settings suggests this technique could be useful in civilian contexts such as outdoor life - saving emergency surgery or in mass casualties where , e . g . amputation and rapid extrication were required .
### Output Text:
Experience in war / tropical settings suggests this technique could be useful in civilian contexts such as outdoor life - saving emergency surgery or in mass casualties where , e . g . amputation and rapid extrication were required . 