I honestly don't know what can be done.
They won’t thank you until after they see someone being burned.
Right now we have had effects but it’s all akin to feeling heat, or coughing from smoke but not actually being burned. Also the heat and smoke randomly shifts to other people so it isn’t consistently hurting anyone.
What’s worse is that we either all escape the building together or we all die together. No one can just choose to believe the theory of the unseen flame and get out alive on their own.
OK, I did use the wrong word there (looking it up, "alarmism" carries different connotations to what I thought), but frankly that's beside the point.
If you want to enact real change (getting people out of the building), and yelling at them about how they're going to die for 4 hours straight has been ineffective, perhaps it's time to try a different strategy.