If there is an emergency, let your team mark themselves safe by adding reactions to a bot's slack message.
Create a custom integration for your team, you'll need a bot and a slash command. Then launch with docker:
docker run -d \
-e SC_SLACK_TOKEN=YOUR_BOT_TOKEN \
-e SC_SLASH_COMMAND_TOKEN=YOUR_SLASH_COMMAND_TOKEN \
-p 80:8080 \
quay.io/joel/safetybot
Assuming you've called the slash command "safetycheck" and the bot is called "safetybot":
/invite safetybot
/safetycheck
Then you'll get a message asking people in the channel to check in, and safetybot will update the message attachments with who has yet to check in by adding a reaction.
Obviously, if a user removes their reaction, they are still counted. If they add multiple reactions they are only counted once, etc.