You could send a few messages with random intervals.
If you make the interval a few times larger than the message duration (3 to 20 times random), and still have about 5 short messages within a second, the collision is a lot less likely to happen.
Do you use a flame detector or a smoke detector ?
A flame detector could detect a fire faster, but doesn't detect something smoldering underneath something.
If you let the detectors send messages on their own, why not combine that with requesting data from the detectors ? You could use that to request more data, or the battery status.