During transfill, if the donor's warning device is not sounding, what should be checked next?

The status of the HUD/control module is crucial during the transfill process as it provides critical information regarding the pressure, battery status, and any potential alarms or issues with the SCBA. If the donor's warning device is not sounding, checking the HUD/control module can help verify whether the transfill operation is functioning properly and if the system is detecting the need for alarm signals. It enables the user to assess any potential failure in indicators or alerts that could compromise safety during the refill process.

Additionally, monitoring the HUD/control module can reveal important diagnostics that may indicate whether the SCBA is functioning within the safe operational limits, thereby ensuring the safety of the user during their operations.