While most typically only test and document that "cranial nerves II - XII are intact" when examining a patient, I would argue that cranial nerve I should also be tested in all head injury cases wherein there was significant facial/nasal trauma
Direct blows to the face, by way of airbag deployment, dash board trauma, or assault, for example, can easily cause the ethmoid bone (see image below) to fracture leaving the olfactory nerve exposed to potential trauma as it crosses the cribiform plate.
Shearing of this nerve can cause irreversible anosmia or hyposmia (inability or decreased ability to smell, respectively).
The easiest, most effective way to test cranial nerve I is one nostril at a time (occlude the one not being tested), using items such as coffee, peppermint oil, or cloves. More annoying smells like that of an alcohol prep or benzoin, can also be used and would likely be more readily accessible in an emergency department.