https://www.ecfr.gov/current/title-47/chapter-I/subchapter-D/part-90?toc=1

FCC 90.403C - Keep It Short:

• Licensees must restrict all transmissions to the minimum practical time and employ efficient procedures to maximize the spectrum use.

FCC 90.403D - Life Safety Has First Priority:

• Communications involving the safety of life or property must be given priority by all licensees.

FCC 90.403E - Don’t Interfere:

• Licensees must take precautions to avoid causing harmful interference, including monitoring the frequency for ongoing communications.

FCC 90.405 - Transmit Only What is Necessary:

• Communications must relate directly to safety-of-life or property, activities necessary for license eligibility, or testing to ensure proper station operation.