With the dangerous temperatures, Marines at Camp Lejeune saw black flags across the base for most of the day, warning them of the excessive heat.
The temperature reached 98 degrees with the heat index well into the hundreds.
The black flag is the highest level in the Marine Corps automated heat stress system. And although it doesn't stop all training, it changes some of the guidelines that are followed while the flag is on the mast.
Each flag color has a specific work to rest ratio that is followed. For example, on a black flag day, even easy work has a limit of 50 minutes before a 10 minute break
The black flag is raised when equipment on base reaches 90-degrees and above.