To mark yourself safe on Facebook during a crisis or emergency, follow these steps:

1. Open the Facebook app or website.
2. Go to the search bar and type "Crisis Response" to open the Crisis Response page.
3. On the Crisis Response page, find the current crisis or disaster relevant to your location.
4. Tap or click on the crisis to open its page.
5. You will see the option to mark yourself safe, usually labeled "I'm Safe." Click or tap this button.
6. This action will notify your Facebook friends and share a post on your timeline indicating that you are safe.

If you receive a notification from Facebook asking if you are safe during a crisis, simply click "I'm Safe" to mark yourself safe quickly. You can also check the safety status of friends in the affected area by going to the Crisis Response page, selecting the crisis, and viewing lists of friends who are marked safe or not yet marked safe. This ensures your loved ones are informed about your well-being during emergencies and helps keep everyone connected.